LTM8055IY - LINEAR TECHNOLOGY

LTM8055

8055f

For more information www.linear.com/LTM8055

Typical applicaTion

FeaTures DescripTion

36VIN, 8.5A Buck-Boost

µModule Regulator

The LT M

8055 is a 36VIN, buck-boost µModule

(micromodule) regulator. Included in the package are the

switching controller, power switches, inductor and support

components. A resistor to set the switching frequency, a

resistor divider to set the output voltage, and input and

output capacitors are all that are needed to complete the

design. Other features such as input and output average

current regulation may be implemented with just a few

components. The LTM8055 operates over an input volt-

age range of 5V to 36V, and can regulate output voltages

between 1.2V and 36V. The SYNC input and CLKOUT

output allow easy synchronization.

The LTM8055 is housed in a compact overmolded ball

grid array (BGA) package suitable for automated assembly

by standard surface mount equipment. The LTM8055 is

RoHS compliant.

12VOUT from 5VIN to 36VIN Buck-Boost Regulator

applicaTions

n Complete Buck-Boost Switch Mode Power Supply

n VOUT Equal, Greater, Less Than VIN

n Wide Input Voltage Range: 5V to 36V

n 12V/3A Output from 6VIN

n 12V/6A Output from 12VIN

n 12V/8.5A Output from 24VIN

n Up to 97.5% Efficient

n Adjustable Input and Output Average Current Limits

n Input and Output Current Monitors

n Parallelable for Increased Output Current

n Wide Output Voltage Range: 1.2V to 36V

n Selectable Switching Frequency: 100kHz to 800kHz

n Synchronization from 200kHz to 700kHz

n 15mm × 15mm × 4.92mm BGA Package

n High Power Battery-Operated Devices

n Industrial Control

n Solar Powered Voltage Regulator

n Solar Powered Battery Charging

L, LT , LT C , LT M , Linear Technology, the Linear logo, µModule and Burst Mode are registered

trademarks of Linear Technology Corporation. All other trademarks are the property of their

respective owners.

Maximum Output Current and

Efficiency vs VIN

VIN (V)

OUTPUT CURRENT (A)

EFFICIENCY (%)

8055 TA01b

402010 30

OUTPUT

CURRENT

EFFICIENCY

VIN

SVIN

IIN

GNDLL MODE

LTM8055

IOUT

VOUT

CLKOUT

IINMON

IOUTMON

RUN

CTL

SYNC

COMP

11.0k

8055 TA01a

22µF

25V

68µF

VOUT

12V

4.7µF

50V

×2

VIN

5V TO 36V

36.5k

600kHz

100k

LTM8055

8055f

For more information www.linear.com/LTM8055

pin conFiguraTionabsoluTe MaxiMuM raTings

VIN, SVIN, VOUT, RUN, IIN, IOUT Voltage .....................40V

FB, SYNC, CTL, MODE Voltage ...................................6V

IINMON, IOUTMON Voltage .............................................6V

LL Voltage .................................................................15V

Maximum Junction Temperature (Notes 2, 3) ....... 125°C

Storage Temperature.............................. –55°C to 125°C

Peak Solder Reflow Body Temperature ................. 245°C

(Note 1)

BANK 2

VOUT

IOUT LL

CLKOUT

RT FB SS

MODE SYNC

COMP

CTL

KJ LHGFEDCB

BGA PACKAGE

121-LEAD (15mm × 15mm × 4.92mm)

BANK 1

GND

BANK 3

VIN

TOP VIEW

SVIN

IIN

RUN

IINMON

IOUTMON

GND

TJMAX = 125°C, θJA = 17.1°C/W, θJCbottom = 7.8°C/W, θJCtop = 17.5°C/W, θJB = 7.1°C/W,

WEIGHT = 2.8g, θ VALUES DETERMINED PER JEDEC JESD51-9, 51-12

orDer inForMaTion

PART NUMBER TERMINAL FINISH PART MARKING* PACKAGE

TYPE

MSL

RATING

TEMPERATURE RANGE

(SEE NOTE 2)

DEVICE FINISH CODE

LTM8055EY#PBF SAC305 (RoHS) LTM8055Y e1 BGA 3 –40°C to 125°C

LTM8055IY#PBF SAC305 (RoHS) LTM8055Y e1 BGA 3 –40°C to 125°C

LTM8055IY SnPb(63/37) LTM8055Y e0 BGA 3 –40°C to 125°C

LTM8055MPY#PBF SAC305 (RoHS) LTM8055Y e1 BGA 3 –55°C to 125°C

LTM8055MPY SnPb(63/37) LTM8055Y e0 BGA 3 –55°C to 125°C

Consult Marketing for parts specified with wider operating temperature

ranges. *Device temperature grade is indicated by a label on the shipping

container. Pad or ball finish code is per IPC/JEDEC J-STD-609.

• Terminal Finish Part Marking:

www.linear.com/leadfree

• Recommended LGA and BGA PCB Assembly and Manufacturing

Procedures:

www.linear.com/umodule/pcbassembly

• LGA and BGA Package and Tray Drawings:

www.linear.com/packaging

LTM8055

8055f

For more information www.linear.com/LTM8055

elecTrical characTerisTics

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. RUN = 1.5V unless otherwise noted. (Note 2)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Input Voltage VIN = SVIN l5.0 V

Output DC Voltage FB = VOUT Through 100k

RFB = 100k/3.40k

1.2

Output DC Current VIN = 6V, VOUT = 12V

VIN = 24V, VOUT = 12V

8.5

Quiescent Current Into VIN (Tied to SVIN) RUN = 0.3V (Disabled)

No Load, MODE = 0.3V (DCM)

No Load, MODE = 1.5V (FCM)

0.1

100

µA

Output Voltage Line Regulation 5V < VIN < 36V, IOUT = 1A 0.5 %

Output Voltage Load Regulation VIN = 12V, 0.1A < IOUT < 6A 0.5 %

Output RMS Voltage Ripple VIN = 12V, IOUT = 3A 25 mV

Switching Frequency RT = 453k

RT = 24.9k

100

800

kHz

Voltage at FB Pin

1.188

1.176

1.212

1.220

RUN Falling Threshold LTM8055 Stops Switching l1.15 1.25 V

RUN Hysteresis LTM8055 Starts Switching 25 mV

RUN Low Threshold LTM8055 Disabled 0.3 V

RUN Pin Current RUN = 1V

RUN = 1.6V

2 3 5

100

µA

IIN Bias Current 90 µA

Input Current Sense Threshold (IIN-VIN)l44 56 mV

IOUT Bias Current 20 µA

Output Current Sense Threshold (VOUT-IOUT) VCTL = Open

54.5

61.5

IINMON Voltage LTM8055 in Input Current Limit 0.96 1.04 V

IOUTMON Voltage LTM8055 in Output Current Limit 1.14 1.26 V

CTL Input Bias Current VCTL = 0V 22 µA

SS Pin Current VSS = 0V 35 µA

CLKOUT Output High 10k to GND 4 V

CLKOUT Output Low 10k to 5V 0.7 V

SYNC Input Low Threshold 0.3 V

SYNC Input High Threshold 1.5 V

SYNC Bias Current SYNC = 1V 11 µA

MODE Input Low Threshold 0.3 V

MODE Input High Threshold 1.5 V

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2: The LTM8055E is guaranteed to meet performance specifications

from 0°C to 125°C internal. Specifications over the full –40°C to

125°C internal operating temperature range are assured by design,

characterization and correlation with statistical process controls. The

LTM8055I is guaranteed to meet specifications over the full –40°C

to 125°C internal operating temperature range. The LTM8055MP is

guaranteed to meet specifications over the full –55°C to 125°C internal

operating temperature range. Note that the maximum internal temperature

is determined by specific operating conditions in conjunction with board

layout, the rated package thermal resistance and other environmental

factors.

Note 3: The LTM8055 contains overtemperature protection that is

intended to protect the device during momentary overload conditions. The

internal temperature exceeds the maximum operating junction temperature

when the overtemperature protection is active. Continuous operation

above the specified maximum operating junction temperature may impair

device reliability.

LTM8055

8055f

For more information www.linear.com/LTM8055

Typical perForMance characTerisTics

Efficiency vs Output Current

(12VOUT)

Efficiency vs Output Current

(18VOUT)

Efficiency vs Output Current

(24VOUT)

Efficiency vs Output Current

(36VOUT)

Input Current vs Output Current

(3.3VOUT)

Input Current vs Output Current

(5VOUT)

Efficiency vs Output Current

(3.3VOUT)

Efficiency vs Output Current

(5VOUT)

Efficiency vs Output Current

(8VOUT)

TA = 25°C, unless otherwise noted.

OUTPUT CURRENT (A)

EFFICIENCY (%)

100

8055 G01

1042 6 8

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

EFFICIENCY (%)

100

8055 G02

1042 6 8

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

EFFICIENCY (%)

100

8055 G03

1042 6 8

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

EFFICIENCY (%)

100

8055 G04

3 6 9

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

EFFICIENCY (%)

100

8055 G05

42 6 8

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

EFFICIENCY (%)

100

8055 G06

3 4 50 1 2 6 7

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

EFFICIENCY (%)

100

8055 G07

3 40 1 2 5

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

INPUT CURRENT (A)

8055 G08

6 80 2 4 10

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

INPUT CURRENT (A)

8055 G09

6 80 2 4 10

5VIN

12VIN

24VIN

36VIN

LTM8055

8055f

For more information www.linear.com/LTM8055

Typical perForMance characTerisTics

Input Current vs Output Current

(24VOUT)

Input Current vs Output Current

(36VOUT) Maximum Output Current vs VIN

Maximum Output Current vs VIN

Temperature Rise vs Output

Current (3.3VOUT)

Temperature Rise vs Output

Current (5VOUT)

Input Current vs Output Current

(8VOUT)

Input Current vs Output Current

(12VOUT)

Input Current vs Output Current

(18VOUT)

TA = 25°C, unless otherwise noted.

OUTPUT CURRENT (A)

INPUT CURRENT (A)

8055 G10

6 80 2 4 10

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

INPUT CURRENT (A)

8055 G11

90 3 6

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

INPUT CURRENT (A)

8055 G12

6 80 2 4

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

INPUT CURRENT (A)

8055 G13

60 2 4

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

INPUT CURRENT (A)

8055 G14

3 4 50 1 2

5VIN

12VIN

24VIN

36VIN

VIN (V)

OUTPUT CURRENT (A)

8055 G15

30 400 10 20

3.3VOUT

5VOUT

8VOUT

VIN (V)

OUTPUT CURRENT (A)

8055 G16

30 400 10 20

12VOUT

18VOUT

24VOUT

36VOUT

OUTPUT CURRENT (A)

TEMPERATURE RISE (°C)

100

8055 G17

6 8 100 2 4

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

TEMPERATURE RISE (°C)

100

8055 G18

6 8 100 2 4

5VIN

12VIN

24VIN

36VIN

LTM8055

8055f

For more information www.linear.com/LTM8055

Typical perForMance characTerisTics

Temperature Rise vs Output

Current (24VOUT)

Temperature Rise vs Output

Current (36VOUT)

Output Voltage Ripple, Unmodified

DC2017A Demo Board 12VOUT

Maximum Output Current vs

CTL Voltage, Unmodified

DC2017A, 12VIN

Start-Up Behavior, DC2017A,

24VIN, 3A Resistive Load

Temperature Rise vs Output

Current (8VOUT)

Temperature Rise vs Output

Current (12VOUT)

Temperature Rise vs Output

Current (18VOUT)

TA = 25°C, unless otherwise noted.

OUTPUT CURRENT (A)

TEMPERATURE RISE (°C)

100

8055 G19

6 8 100 2 4

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

TEMPERATURE RISE (°C)

100

8055 G20

6 80 2 4

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

TEMPERATURE RISE (°C)

100

8055 G21

6 80 2 4

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

TEMPERATURE RISE (°C)

100

8055 G22

60 2 4

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (A)

TEMPERATURE RISE (°C)

100

8055 G23

50 1 2 3 4

5VIN

12VIN

24VIN

36VIN

2V/DIV

8055 G25

500µs/DIV

NO CSS

CSS = 0.022µF

CSS = 0.22µF

CTL VOLTAGE (V)

OUTPUT CURRENT (A)

8055 G26

1.2 1.410 0.40.2 0.80.6

24VIN

6A LOAD

(BUCK)

100mV/DIV

12VIN

6A LOAD

(BUCK-BOOST)

100mV/DIV

6VIN

3A LOAD

(BOOST)

100mV/DIV

8055 G24

0.5µs/DIV

MEASURED WITH HP461N

150MHz AMPLIFIER

LTM8055

8055f

For more information www.linear.com/LTM8055

pin FuncTions

GND (Bank 1, Pin L1): Tie these GND pins to a local ground

plane below the LTM8055 and the circuit components.

In most applications, the bulk of the heat flow out of the

LTM8055 is through these pads, so the printed circuit

design has a large impact on the thermal performance of

the part. See the PCB Layout and Thermal Considerations

sections for more details. Return the RFB1/RFB2 feedback

divider to this net.

VOUT (Bank 2): Power Output Pins. Apply output filter

capacitors between these pins and GND pins.

VIN (Bank 3): Input Power. The VIN pin supplies current to

the LTM8055’s internal power switches and to one terminal

of the optional input current sense resistor. This pin must

be locally bypassed with an external, low ESR capacitor;

see Table 1 for recommended values.

IOUT (Pin D1): Output Current Sense. Tie this pin to the

output current sense resistor. The output average current

sense threshold is 58mV, so the LTM8055 will regulate

the output current to 58mV/RSENSE, where RSENSE is the

value of the output current sense resistor in ohms. The

load is powered through the sense resistor connected at

this pin. Tie this pin to VOUT if no output current sense

resistor is used. Keep this pin within ±0.5V of VOUT under

all conditions.

LL (Pin F1): Light Load Indicator. This pin indicates that

the output current, as sensed through the resistor con-

nected between VOUT and IOUT, is approximately equivalent

to 10mV or less. Its state is meaningful only if a current

sense resistor is applied between VOUT and IOUT. This is

useful to change the switching behavior of the LTM8055

in light load conditions.

SVIN (Pins F10, F11): Controller Power Input. Apply a

separate voltage above 5V if the LTM8055 is required to

operate when the main power input (VIN) is below 5V.

Bypass these pins with a high quality, low ESR capacitor.

If a separate supply is not used, connect these pins to VIN.

CLKOUT (Pin G1): Clock Output. Use this pin as a clock

source when synchronizing other devices to the switch-

ing frequency of the LTM8055. When this function is not

used, leave this pin open.

MODE (Pin G2): Switching Mode Input. The LTM8055 oper-

ates in forced continuous mode when MODE is open, and

can operate in discontinuous switching mode when MODE

is low. In discontinuous switching mode, the LTM8055

will block reverse inductor current. This pin is normally

left open or tied to LL. This pin may be tied to GND for the

purpose of blocking reverse current if no output current

sense resistor is used.

RT (Pin H1): Timing Resistor. The RT pin is used to program

the switching frequency of the LTM8055 by connecting a

resistor from this pin to ground. The range of oscillation is

100kHz to 800kHz. The Applications Information section of

the data sheet includes a table to determine the resistance

value based on the desired switching frequency. Minimize

capacitance at this pin.

SYNC (Pin H2): External Synchronization Input. The SYNC

pin has an internal pull-down resistor. See the Synchroni-

zation section in Applications Information for details. Tie

this pin to GND when not used.

FB (Pin J1): Output Voltage Feedback. The LTM8055

regulates the FB pin to 1.2V. Connect the FB pin to a

resistive divider between the output and GND to set the

output voltage. See Table 1 for recommended FB divider

resistor values.

COMP (Pin J2): Compensation Pin. The LTM8055 is

equipped with internal compensation that works well with

most applications. In some cases, the performance of the

LTM8055 can be enhanced by modifying the control loop

compensation by applying a capacitor or RC network to

this pin.

SS (Pin K1): Soft-Start. Connect a capacitor from this pin

to GND to increase the soft-start time. Soft-start reduces

the input power source’s surge current by gradually in-

creasing the controller’s current limit. Larger values of the

soft-start capacitor result in longer soft-start times. If no

soft-start is required, leave this pin open.

CTL (Pin K2): Current Sense Adjustment. Apply a voltage

below 1.2V to reduce the current limit threshold of IOUT.

Drive CTL to less than 50mV to stop switching. The CTL

pin has an internal pull-up resistor to 2V. If not used,

leave open.

LTM8055

8055f

For more information www.linear.com/LTM8055

pin FuncTions

IOUTMON (Pin L2): Output Current Monitor. This pin pro-

duces a voltage that is proportional to the voltage between

VOUT and IOUT. IOUTMON will equal 1.2V when VOUT – IOUT

= 58mV. This feature is generally useful only if a current

sense resistor is applied between VOUT and IOUT.

IINMON (Pin L3): Input Current Monitor. This pin produces

a voltage that is proportional to the voltage between IIN

and VIN. IINMON will equal 1V when IIN – VIN = 50mV. This

feature is generally useful only if a current sense resistor

is applied between VIN and IIN.

RUN (Pin L4): LTM8055 Enable. Raise the RUN pin voltage

above 1.2V for normal operation. Above 1.2V (typical), but

below 6V, the RUN pin input bias current is less than 1μA.

Below 1.2V and above 0.3V, the RUN pin sinks 3μA so

the user can define the hysteresis with the external resis-

tor selection. This will also reset the soft-start function.

If RUN is 0.3V or less, the LTM8055 is disabled and the

SVIN quiescent current is below 1μA.

IIN (Pin L9): Input Current Sense. Tie this pin to the input

current sense resistor. The input average current sense

threshold is 50mV, so the LTM8055 will regulate the input

current to 50mV/RSENSE, where RSENSE is the value of the

input current sense resistor in ohms. Tie to VIN when not

used. Keep this pin within ±0.5V of VIN under all conditions.

block DiagraM

0.2µF

4.7µH

0.47µF

50V

0.1µF

CTL

COMP RT SYNC

100k

IOUTMON

8055 BD

IINMON

CLKOUT

IOUT

VOUT

GND

RUN

IIN

VIN

SVIN

BUCK-BOOST CONTROLLER

LLMODE

LTM8055

8055f

For more information www.linear.com/LTM8055

operaTion

The LTM8055 is a standalone nonisolated buck-boost

switching DC/DC power supply. The buck-boost topol-

ogy allows the LTM8055 to regulate its output voltage for

input voltages both above and below the magnitude of the

output. The maximum output current depends upon the

input voltage. Higher input voltages yield higher maximum

output current.

This converter provides a precisely regulated output volt-

age programmable via an external resistor divider from

1.2V to 36V. The input voltage range is 5V to 36V, but the

LTM8055 may be operated at lower input voltages if SVIN

is powered by a voltage source above 5V. A simplified

block diagram is given on the previous page.

The LTM8055 contains a current mode controller, power

switching elements, power inductor and a modest amount

of input and output capacitance. The LTM8055 is a fixed

frequency PWM regulator. The switching frequency is set

by connecting the appropriate resistor value from the RT

pin to GND.

The output voltage of the LTM8055 is set by connecting

the FB pin to a resistor divider between VOUT and GND.

In addition to regulating its output voltage, the LTM8055

is equipped with average current control loops for both the

input and output. Add a current sense resistor between IIN

and VIN to limit the input current below some maximum

value. The IINMON pin reflects the current flowing though

the sense resistor between IIN and VIN.

A current sense resistor between VOUT and IOUT allows

the LTM8055 to accurately regulate its output current to

a maximum value set by the value of the sense resistor.

When the resistor is present, the IOUTMON pin reflects the

output current flowing through VOUT.

In general, the LTM8055 should be used with an output

sense resistor to limit the maximum output current, as

buck-boost regulators are capable of delivering large

currents when the output voltage is lower than the input,

if demanded.

Furthermore, while the LTM8055 does not require an

output sense resistor to operate, it uses information from

the sense resistor to optimize its performance. If an out-

put sense resistor is not used, the efficiency or output

ripple may degrade, especially if the current through the

integrated inductor is discontinuous. In some cases, an

output sense resistor is required to adequately protect the

LTM8055 against output overload or short-circuit.

A voltage less than 1.2V applied to the CTL pin reduces

the maximum output current. Drive CTL to about 50mV

to stop switching. The current flowing through the sense

resistor is reflected by the output voltage of the IOUTMON pin.

Driving the SYNC pin will synchronize the LTM8055 to an

external clock source. The CLKOUT pin sources a signal

that is the same frequency but approximately 180° out of

phase with the internal oscillator.

If more output current is required than a single LTM8055

can provide, multiple devices may be operated in parallel.

Refer to the Parallel Operation section of Applications

Information for more details.

An internal regulator provides power to the control circuitry

and the gate driver to the power MOSFETs. This internal

regulator draws power from the SVIN pin. The RUN pin is

used to place the LTM8055 in shutdown, disconnecting

the output and reducing the input current to less than 1μA.

The LTM8055 is equipped with a thermal shutdown that

inhibits power switching at high junction temperatures.

The activation threshold of this function is above 125°C

to avoid interfering with normal operation, so prolonged

or repetitive operation under a condition in which the

thermal shutdown activates may damage or impair the

reliability of the device.

LTM8055

8055f

For more information www.linear.com/LTM8055

applicaTions inForMaTion

For most applications, the design process is straight for-

ward, summarized as follows:

1. Look at Table 1 and find the row that has the desired

input range and output voltage.

2. Apply the recommended CIN, COUT, RFB1/RFB2 and RT

values.

3. Apply the output sense resistor to set the output current

limit. The output current is limited to 58mV/RSENSE,

where RSENSE is the value of the output current sense

resistor in ohms.

While these component combinations have been tested for

proper operation, it is incumbent upon the user to verify

proper operation over the intended system’s line, load and

environmental conditions. Bear in mind that the maximum

output current is limited by junction temperature, the rela-

tionship between the input and output voltage magnitude

and other factors. Please refer to the graphs in the Typical

Performance Characteristics section for guidance.

The maximum frequency (and attendant RT value) at

which the LTM8055 should be allowed to switch is given

in Table 1 in the fMAX column, while the recommended

frequency (and RT value) for optimal efficiency over the

given input condition is given in the fOPTIMAL column.

There are additional conditions that must be satisfied if

the synchronization function is used. Please refer to the

Synchronization section for details.

Note that Table 1 calls out both ceramic and electrolytic

output capacitors. Both of the capacitors called out in

the table must be applied to the output. The electrolytic

capacitors in Table 1 are described by voltage rating,

value and ESR. The voltage rating of the capacitor may

be increased if the application requires a higher voltage

stress derating. The LTM8055 can tolerate variation

in the ESR; other capacitors with different ESR may

be used, but the user must verify proper operation

over line, load and environmental conditions. Table 2

gives the description and part numbers of electrolytic

capacitors used in the LTM8055 development testing and

design validation.

Table 1. Recommended Component Values and Configuration (TA = 25°C)

VIN RANGE VOUT CIN COUT RFB1/RFB2 fOPTIMAL (kHz) RT(OPTIMAL) fMAX (kHz) RT(MAX)

5V to 24V 3.3V 2 × 4.7µF, 50V, X5R, 0805 22µF, 6.3V, X5R, 0805

100µF, 6V, 75mΩ, Electrolytic

100k/56.2k 600 36.5k 800 24.9k

5V to 28V 5V 2 × 4.7µF, 50V, X5R, 0805 22µF, 6.3V, X5R, 0805

100µF, 6V, 75mΩ, Electrolytic

100k/31.6k 550 39.2k 800 24.9k

5V to 31V 8V 2 × 4.7µF, 50V, X5R, 0805 47µF, 10V, X5R, 1206

100µF, 16V, 100mΩ, Electrolytic

100k/17.4k 500 45.3k 800 24.9k

5V to 36V 12V 2 × 4.7µF, 50V, X5R, 1210 22µF, 25V, X5R, 0805

68µF, 16V, 200mΩ, Electrolytic

100k/11k 600 36.5k 800 24.9k

5V to 36V 18V 2 × 4.7µF, 50V, X7R, 1210 2 x 22µF, 25V, X5R, 1210

47µF, 25V, 900mΩ, Electrolytic

100k/6.98k 500 45.3k 800 24.9k

5V to 36V 24V 2 × 4.7µF, 50V, X7R, 1210 22µF, 25V, X5R, 1210

33µF, 35V 300mΩ, Electrolytic

100k/5.23k 650 31.6k 800 24.9k

5.5V to 36V 36V 2 × 4.7µF, 50V, X7R, 1210 10µF, 50V, X5R, 1206

10µF, 50V 120mΩ, Electrolytic

100k/3.40k 650 31.6k 800 24.9k

Notes: An input bulk capacitor is required. The output capacitance uses a combination of a ceramic and electrolytic in parallel. Other combinations of

resistor values for the RFB network are acceptable.

Table 2. Electrolytic Caps Used in LTM8055 Testing

DESCRIPTION MANUFACTURER PART NUMBER

100µF, 6V, 75mΩ, Tantalum C Case AVX TPSC107M006R0075

100µF, 16V, 100mΩ, Tantalum Y Case AVX TPSY107M016R0100

68µF, 16V, 200mΩ, Tantalum C Case AVX TPSC686M016R0200

47µF, 25V, 900mΩ, Tantalum D Case AVX TAJD476M025R

33µF, 35V, 300mΩ, Tantalum D Case AVX TPSD336M035R0300

10µF, 50V, 120mΩ, Aluminum 6.3 × 6mm case Suncon 50HVP10M

LTM8055

8055f

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applicaTions inForMaTion

Capacitor Selection Considerations

The CIN and COUT capacitor values in Table 1 are the

minimum recommended values for the associated oper-

ating conditions. Applying capacitor values below those

indicated in Table 1 is not recommended, and may result

in undesirable operation. Using larger values is generally

acceptable, and can yield improved dynamic response, if

it is necessary. Again, it is incumbent upon the user to

verify proper operation over the intended system’s line,

load and environmental conditions.

Ceramic capacitors are small, robust and have very low

ESR. However, not all ceramic capacitors are suitable.

X5R and X7R types are stable over temperature and ap-

plied voltage and give dependable service. Other types,

including Y5V and Z5U have very large temperature and

voltage coefficients of capacitance. In an application cir-

cuit they may have only a small fraction of their nominal

capacitance resulting in much higher output voltage ripple

than expected.

A final precaution regarding ceramic capacitors concerns

the maximum input voltage rating of the LTM8055. A

ceramic input capacitor combined with trace or cable

inductance forms a high Q (underdamped) tank circuit.

If the LTM8055 circuit is plugged into a live supply, the

input voltage can ring to twice its nominal value, possi-

bly exceeding the device’s rating. This situation is easily

avoided; see the Hot-Plugging Safely section.

Frequency Selection

The LTM8055 uses a constant frequency PWM architec-

ture that can be programmed to switch from 100kHz to

800kHz by tying a resistor from the RT pin to ground.

Table 3 provides a list of RT resistor values and their re-

sultant frequencies.

Table 3. Switching Frequency vs RT Value

FREQUENCY RT VALUE (kΩ)

100 453

200 147

300 84.5

400 59

500 45.3

600 36.5

700 29.4

800 24.9

An external resistor from RT to GND is required. Do not

leave this pin open, even when synchronizing to an ex-

ternal clock. When synchronizing the switching of the

LTM8055 to an external signal source, the frequency range

is 200kHz to 700kHz.

Operating Frequency Trade-Offs

It is recommended that the user apply the optimal RT

value given in Table 1 for the input and output operating

condition. System level or other considerations, however,

may necessitate another operating frequency. While the

LTM8055 is flexible enough to accommodate a wide range

of operating frequencies, a haphazardly chosen one may

result in undesirable operation under certain operating or

fault conditions. A frequency that is too high can reduce

efficiency, generate excessive heat or even damage the

LTM8055 if the output is overloaded or short circuited.

A frequency that is too low can result in a final design

that has too much output ripple, too large of an output

capacitor or is unstable.

Parallel Operation

Tw o or more LTM8055s may be combined to provide

increased output current by configuring them as a mas-

ter and a slave, as shown in Figure 1. Each LTM8055 is

equipped with an IOUTMON and a CTL pin. The IOUTMON

pin’s 0 to 1.2V signal reflects the current passing through

the output sense resistor, while a voltage less than 1.2V

applied to the CTL pin will limit the current passing through

the output sense resistor. By applying the voltage of the

master’s IOUTMON pin to the slave’s CTL pin, the two units

LTM8055

8055f

For more information www.linear.com/LTM8055

applicaTions inForMaTion

will source the same current to the load, assuming each

LTM8055 output current sense resistor is the same value.

Paralleled LTM8055s should normally be allowed to switch

in discontinuous mode to prevent current from flowing

from the output of one unit into another; that is, the

MODE pin should be tied to LL. In some cases, operating

the master in forced continuous (MODE open) and the

slaves in discontinuous mode (MODE = LL) is desirable.

If so, current from the output can flow into the master’s

input. Please refer to Input Precaution in this section for

a discussion of this behavior.

Minimum Input Voltage and RUN

The LTM8055 needs a minimum of 5V for proper opera-

tion, but system parameters may dictate that the device

operate only above some higher input voltage. For ex-

ample, a LTM8055 may be used to produce 12VOUT, but

the input power source may not be budgeted to provide

enough current if the input supply voltage is below 8V.

The RUN pin has a typical falling voltage threshold of

1.2V and a typical hysteresis of 25mV. In addition, the

pin sinks 3µA below the RUN threshold. Based upon the

above information and the circuit shown in Figure 2, the

VIN rising (turn-on) threshold is:

VIN = 3µA •R1

( )

+1.225V

R1+R2

and the VIN falling turn-off threshold is:

VIN =1.2

R1+R2

RUN

LTM8055

VIN

8055 F02

Figure 2. This Simple Resistor Network Sets the Minimum

Operating Input Voltage Threshold with Hysteresis

Figure 1. Tw o or More LTM8055s May Be Connected in a

Master/Slave Configuration for Increased Output Current

The design of a master-slave configuration is straight

forward:

1. Apply the FB resistor network to the master, choosing

the proper values for the desired output voltage. Sug-

gested values for popular output voltages are provided

in Table 1.

2. Apply a FB resistor network to the individual slaves

so that the resulting output is higher than the desired

output voltage.

3. Apply the appropriate output current sense resistors

between VOUT and IOUT. If the same value is used for the

master and slave units, they will share current equally.

4. Connect the master IOUTMON to the slaves’ CTL pin

through a unity gain buffer. The unity gain buffer is

required to isolate the output impedance of the LTM8055

from the integrated pull-up on the CTL pins.

5. Tie the outputs together.

Note that this configuration does not require the inputs to

be tied together, making it simple to power a single heavy

load from multiple input sources. Ensure that each input

power source has sufficient voltage and current sourcing

capability to provide the necessary power. Please refer

to the Maximum Output Current vs VIN and Input Current

vs Output Current curves in the Typical Performance

Characteristics section for guidance.

Minimum Input Voltage and SVIN

The minimum input voltage of the LTM8055 is 5V, but this

is only if VIN and SVIN are tied to the same voltage source.

If SVIN is powered from a power source at or above 5VDC,

VIN can be allowed to fall below 5V and the LTM8055 can

MASTER

VOUT

IOUT

OUTPUT CURRENT

SENSE RESISTOR

OUTPUT CURRENT

SENSE RESISTOR

UNITY GAIN

BUFFER

IOUTMON

CTL

VOUT

IOUT

SLAVE

TO LOAD

8055 F01

LTM8055

8055f

For more information www.linear.com/LTM8055

still operate properly. Some examples of this are provided

in the Typical Applications section.

Soft-Start

Soft-start reduces the input power sources’ surge currents

by gradually increasing the controller’s current. As indicated

in the Block Diagram, the LTM8055 has an internal soft-

start RC network. Depending upon the load and operating

conditions, the internal network may be sufficient for the

application. To increase the soft-start time, simply add a

capacitor from SS to GND.

Output Current Limit (IOUT)

The LTM8055 features an accurate average output current

limit set by an external sense resistor placed between VOUT

and IOUT as shown in Figure 3. VOUT and IOUT internally

connect to a differential amplifier that limits the current

when the voltage VOUT-IOUT reaches 58mV. The current

limit is:

IOUT(LIM) =

58mV

RSENSE

where RSENSE is the value of the sense resistor in ohms.

Most applications should use an output sense resistor as

shown in Figure 3, if practical. The internal buck-boost

power stage is current limited, but is nonetheless capable

of delivering large amounts of current in an overload

condition, especially when the output voltage is much

lower than the input and the power stage is operating as

a buck converter.

tying the LL and MODE pins together can improve perfor-

mance—see Switching Mode in this section.

In high step-down voltage regulator applications, the

internal current limit can be quite high to allow proper

operation. This can potentially damage the LTM8055

in overload or short-circuit conditions. Apply an output

current sense resistor to set an appropriate current limit

to protect the LTM8055 against these fault conditions.

Output Current Limit Control (CTL)

Use the CTL input to reduce the output current limit from

the value set by the external sense resistor applied between

VOUT and IOUT. The typical control range is between 0V

and 1.2V. The CTL pin does not directly affect the input

current limit. If this function is not used, leave CTL open.

Drive CTL to less than about 50mV to stop switching. The

CTL pin has an internal pull-up resistor to 2V.

Input Current Limit (IIN)

Some applications require that LTM8055 draw no more

than some predetermined current from the power source.

Current limited power sources and power sharing are two

examples. The LTM8055 features an accurate input current

limit set by an external sense resistor placed between IIN

and VIN as shown in Figure 4. VIN and IIN internally connect

to a differential amplifier that limits the current when the

voltage IIN-VIN reaches 50mV. The current limit is:

IIN(LIM) =

50mV

SENSE

where RSENSE is the value of the sense resistor in ohms.

If input current limiting is not required, simply tie IIN to VIN.

applicaTions inForMaTion

IOUT

LTM8055

VOUT

RSENSE

8055 F03

LOAD

Figure 3. Set The LTM8055 Output Current Limit with an External

Sense Resistor

Figure 4. Set the LTM8055 Input Current Limit with an

External Sense Resistor

IIN

LTM8055

RSENSE

VIN

POWER

SOURCE

8055 F04

When the voltage across the output sense resistor falls

to about 1/10th of full scale, the LL pin pulls low. If there

is no output sense resistor, and IOUT is tied to VOUT, LL

will be active low. Applying an output sense resistor and

LTM8055

8055f

For more information www.linear.com/LTM8055

Input Current Monitor (IINMON)

The IINMON pin produces a voltage equal to approximately

20 times the voltage of IIN – VIN. Since the LTM8055 input

current limit engages when IIN – VIN = 50mV, IINMON will

be 1V at maximum input current.

Output Current Monitor (IOUTMON)

The IOUTMON pin produces a voltage proportional to the

voltage of VOUT – IOUT. Since the LTM8055 output current

limit engages when VOUT – IOUT = 58mV, IOUTMON will be

1.2V at maximum output current.

Synchronization

The LTM8055 switching frequency can be synchronized to

an external clock using the SYNC pin. Driving SYNC with

a 50% duty cycle waveform is a good choice, otherwise

maintain the duty cycle between about 10% and 90%. When

synchronizing, a valid resistor value (that is, a value that

results in a free-running frequency of 100kHz to 800kHz)

must be connected from RT to GND.

While an RT resistor is required for proper operation, the

value of this resistor is independent of the frequency of

the externally applied SYNC signal. Be aware, however,

that the LTM8055 will switch at the frequency prescribed

by the RT value if the SYNC signal terminates, so choose

an appropriate resistor value.

CLKOUT

The CLKOUT signal reflects the internal switching clock of

the LTM8055. It is phase shifted by approximately 180° with

respect to the leading edge of the internal clock. If CLKOUT

is connected to the SYNC input of another LTM8055, the

two devices will switch about 180° out of phase.

Input Precaution

In applications where the output voltage is deliberately

pulled up above the set regulation voltage or the FB pin is

abruptly driven to a new voltage, the LTM8055 may attempt

to regulate the voltage by removing energy from the load

for a short period of time after the output is pulled up.

Since the LTM8055 is a synchronous switching converter,

it delivers this energy to the input. If there is nothing on the

LTM8055 input to consume this energy, the input voltage

may rise. If the input voltage rises without intervention, it

may rise above the absolute maximum rating, damaging

the part. Carefully examine the input voltage behavior to

see if the application causes it to rise.

In many cases, the system load on the LTM8055 input

bus will be sufficient to absorb the energy delivered by the

μModule regulator. The power required by other devices

will consume more than enough to make up for what

the LTM8055 delivers. In cases where the LTM8055 is

the largest or only power converter, this may not be true

and some means may need to be devised to prevent the

LTM8055’s input from rising too high. Figure 5a shows a

passive crowbar circuit that will dissipate energy during

momentary input overvoltage conditions. The break-down

voltage of the Zener diode is chosen in conjunction with

the resistor R to set the circuit’s trip point. The trip point

is typically set well above the maximum VIN voltage under

normal operating conditions. This circuit does not have

a precision threshold, and is subject to both part-to-part

and temperature variations, so it is most suitable for ap-

plications where the maximum input voltage is much less

than the 40VIN absolute maximum. As stated earlier, this

type of circuit is best suited for momentary overvoltages.

Figure 5a is a crowbar circuit, which attempts to prevent

the input voltage from rising above some level by dumping

energy to GND through a power device. In some cases,

it is possible to simply turn off the LTM8055 when the

input voltage exceeds some threshold. An example of this

circuit is shown in Figure 5b. When the power source on

the output drives VIN above a predetermined threshold,

the comparator pulls down on the RUN pin and stops

switching in the LTM8055. When this happens, the input

capacitance needs to absorb the energy stored within the

LTM8055’s internal inductor, resulting in an additional

voltage rise. This voltage rise depends upon the input

capacitor size and how much current is flowing from the

LTM8055 output to input.

applicaTions inForMaTion

LTM8055

8055f

For more information www.linear.com/LTM8055

Switching Mode

The MODE pin allows the user to select either discontinuous

mode or forced continuous mode switching operation. In

forced continuous mode, the LTM8055 will not skip cycles,

even when the internal inductor current falls to zero or even

reverses direction. This has the advantage of operating at

the same fixed frequency for all load conditions, which can

be useful when designing to EMI or output noise speci-

fications. Forced continuous mode, however, uses more

current at light loads, and allows current to flow from the

load back into the input if the output is raised above the

regulation point. This reverse current can raise the input

voltage and be hazardous if the input is allowed to rise

uncontrollably. Please refer to Input Precautions in this

section for a discussion of this behavior.

Forced continuous operation may provide improved

output regulation when the LTM8055 transitions from

buck, buck-boost or boost operating modes, especially at

lighter loads. In such a case, it can be desirable to oper-

ate in forced continuous mode except when the internal

inductor current is about to reverse. If so, apply a current

sense resistor between VOUT and IOUT and tie the LL and

MODE pins together. The LL pin is low when the current

through the output sense resistor is about one-tenth the

full-scale maximum. When the output current falls to this

level, the LL pin will pull the MODE pin down, putting the

LTM8055 in discontinuous mode, preventing reverse cur-

rent from flowing from the output to the input. In the case

where MODE and LL are tied together, a small capacitor

(~0.1µF) from these pins to GND may improve the light

load transient response by delaying the transition from

the discontinuous to forced continuous switching modes.

MODE may be tied to GND for the purpose of blocking

reverse current if no output current sense resistor is used.

FB Resistor Divider and Load Regulation

The LTM8055 regulates its FB pin to 1.2V, using a resistor

divider to sense the output voltage. The location at which

the output voltage is sensed affects the load regulation.

If there is a current sense resistor between VOUT and

IOUT, and the output is sensed at VOUT, the voltage at the

load will drop by the value of the current sense resistor

multiplied by the output current. If the output voltage can

be sensed at IOUT, the load regulation may be improved.

PCB Layout

Most of the headaches associated with PCB layout have

been alleviated or even eliminated by the high level of

integration of the LTM8055. The LTM8055 is neverthe-

less a switching power supply, and care must be taken to

minimize EMI and ensure proper operation. Even with the

high level of integration, you may fail to achieve specified

operation with a haphazard or poor layout. See Figure 6

for a suggested layout. Ensure that the grounding and

heat sinking are acceptable.

A few rules to keep in mind are:

1. Place the RFB and RT resistors as close as possible to

their respective pins.

applicaTions inForMaTion

VIN

ZENER

DIODE

8055 F05a

LTM8055

LOAD

CURRENT

GND

VOUT

SOURCING

LOAD

VIN

RUN

8055 F05b

10µF

LTM8055

LOAD

CURRENT

GND

VOUT

SOURCING

LOAD

EXTERNAL

REFERENCE

VOLTAGE

–

Figure 5a. The MOSFET Q Dissipates Momentary Energy to

GND. The Zener Diode and Resistor Are Chosen to Ensure That

the MOSFET Turns On Above the Maximum VIN Voltage Under

Normal Operation

Figure 5b. This Comparator Circuit Turns Off the LTM8055 if

the Input Rises Above a Predetermined Threshold. When the

LTM8055 Turns Off, the Energy Stored in the Internal Inductor

Will Raise VIN a Small Amount Above the Threshold

LTM8055

8055f

For more information www.linear.com/LTM8055

2. Place the CIN capacitor as close as possible to the VIN

and GND connection of the LTM8055.

3. Place the COUT capacitor as close as possible to the

VOUT and GND connection of the LTM8055.

4. Minimize the trace resistance between the optional

output current sense resistor, ROUT, and VOUT. Minimize

the loop area of the IOUT trace and the trace from VOUT

to ROUT.

5. Minimize the trace resistance between the optional input

current sense resistor, RIN and VIN. Minimize the loop

area of the IIN trace and the trace from VIN to RIN.

6. Place the CIN and COUT capacitors such that their

ground current flow directly adjacent or underneath

the LTM8055.

7. Connect all of the GND connections to as large a copper

pour or plane area as possible on the top layer. Avoid

breaking the ground connection between the external

components and the LTM8055.

8. Use vias to connect the GND copper area to the board’s

internal ground planes. Liberally distribute these GND

vias to provide both a good ground connection and

thermal path to the internal planes of the printed circuit

board. Pay attention to the location and density of the

thermal vias in Figure 6. The LTM8055 can benefit from

the heat sinking afforded by vias that connect to internal

GND planes at these locations, due to their proximity

to internal power handling components. The optimum

number of thermal vias depends upon the printed

circuit board design. For example, a board might use

very small via holes. It should employ more thermal

vias than a board that uses larger holes.

Hot-Plugging Safely

The small size, robustness and low impedance of ceramic

capacitors make them an attractive option for the input

bypass capacitor of LTM8055. However, these capacitors

can cause problems if the LTM8055 is plugged into a live

supply (see Linear Technology Application Note88 for a

complete discussion). The low loss ceramic capacitor

combined with stray inductance in series with the power

source forms an underdamped tank circuit, and the volt-

age at the VIN pin of the LTM8055 can ring to more than

twice the nominal input voltage, possibly exceeding the

LTM8055’s rating and damaging the part. If the input supply

is poorly controlled or the LTM8055 is hot-plugged into an

energized supply, the input network should be designed

applicaTions inForMaTion

Figure 6. Layout Showing Suggested External Components,

GND Plane and Thermal Vias

ROUT

OUTPUT

SENSE

VOUT SIGNAL VIA

GND

GND/THERMAL VIAS

GND

INPUT

RIN

INPUT

SENSE

8055 F06

COUT

VOUT

IOUT

VIN

CIN

SVIN

LL RT

MODE SYNC

RUN

IIN

IOUT

VOUT SIGNAL VIA

LTM8055

8055f

For more information www.linear.com/LTM8055

to prevent this overshoot. This can be accomplished by

installing a small resistor in series with VIN, but the most

popular method of controlling input voltage overshoot is

to add an electrolytic bulk capacitor to the VIN net. This

capacitor’s relatively high equivalent series resistance

damps the circuit and eliminates the voltage overshoot.

The extra capacitor improves low frequency ripple filter-

ing and can slightly improve the efficiency of the circuit,

though it is likely to be the largest component in the circuit.

Thermal Considerations

The LTM8055 output current may need to be derated if

it is required to operate in a high ambient temperature or

deliver a large amount of continuous power. The amount

of current derating is dependent upon the input voltage,

output power and ambient temperature. The temperature

rise curves given in the Typical Performance Character-

istics section can be used as a guide. These curves were

generated by a LTM8055 mounted to a 58cm2 4-layer FR4

printed circuit board. Boards of other sizes and layer count

can exhibit different thermal behavior, so it is incumbent

upon the user to verify proper operation over the intended

system’s line, load and environmental operating

conditions.

The thermal resistance numbers listed in the Pin Configura-

tion of the data sheet are based on modeling the µModule

package mounted on a test board specified per JESD 51-9

(Test Boards for Area Array Surface Mount Package Thermal

Measurements). The thermal coefficients provided on this

page are based on JESD 51-12 (Guidelines for Reporting

and Using Electronic Package Thermal Information).

For increased accuracy and fidelity to the actual application,

many designers use FEA to predict thermal performance.

To that end, the Pin Configuration of the data sheet typi-

cally gives four thermal coefficients:

θJA – Thermal resistance from junction to ambient.

θJCbottom – Thermal resistance from junction to the bottom

of the product case.

θJCtop – Thermal resistance from junction to top of the

product case.

θJB – Thermal resistance from junction to the printed

circuit board.

While the meaning of each of these coefficients may seem

to be intuitive, JEDEC has defined each to avoid confusion

and inconsistency. These definitions are given in JESD

51-12, and are quoted or paraphrased below:

θJA is the natural convection junction-to-ambient air

thermal resistance measured in a one cubic foot sealed

enclosure. This environment is sometimes referred to as

“still air” although natural convection causes the air to

move. This value is determined with the part mounted to

a JESD 51-9 defined test board, which does not reflect an

actual application or viable operating condition.

θJCbottom is the thermal resistance between the junction

and bottom of the package with all of the component power

dissipation flowing through the bottom of the package. In

the typical µModule converter, the bulk of the heat flows

out the bottom of the package, but there is always heat

flow out into the ambient environment. As a result, this

thermal resistance value may be useful for comparing

packages but the test conditions don’t generally match

the user’s application.

θJCtop is determined with nearly all of the component power

dissipation flowing through the top of the package. As the

electrical connections of the typical µModule converter are

on the bottom of the package, it is rare for an application

to operate such that most of the heat flows from the junc-

tion to the top of the part. As in the case of θJCbottom, this

value may be useful for comparing packages but the test

conditions don’t generally match the user’s application.

θJB is the junction-to-board thermal resistance where

almost all of the heat flows through the bottom of the

µModule converter and into the board, and is really the

sum of the θJCbottom and the thermal resistance of the

bottom of the part through the solder joints and through a

portion of the board. The board temperature is measured

a specified distance from the package, using a 2-sided,

2-layer board. This board is described in JESD 51-9.

Given these definitions, it should now be apparent that none

of these thermal coefficients reflects an actual physical

operating condition of a µModule converter. Thus, none

applicaTions inForMaTion

LTM8055

8055f

For more information www.linear.com/LTM8055

applicaTions inForMaTion

of them can be individually used to accurately predict the

thermal performance of the product. Likewise, it would

be inappropriate to attempt to use any one coefficient to

correlate to the junction temperature versus load graphs

given in the product’s data sheet. The only appropriate way

to use the coefficients is when running a detailed thermal

analysis, such as FEA, which considers all of the thermal

resistances simultaneously.

A graphical representation of these thermal resistances

is given in Figure 7.

The blue resistances are contained within the µModule

converter, and the green are outside.

The die temperature of the LTM8055 must be lower than

the maximum rating of 125°C, so care should be taken in

the layout of the circuit to ensure good heat sinking of the

LTM8055. The bulk of the heat flow out of the LTM8055

is through the bottom of the μModule converter and the

BGA pads into the printed circuit board. Consequently a

poor printed circuit board design can cause excessive

heating, resulting in impaired performance or reliability.

Please refer to the PCB Layout section for printed circuit

board design suggestions.

Figure 7

8055 F07

µMODULE CONVERTER

JUNCTION-TO-CASE (TOP)

RESISTANCE

JUNCTION-TO-BOARD RESISTANCE

JUNCTION-TO-AMBIENT RESISTANCE (JESD 51-9 DEFINED BOARD)

CASE (TOP)-TO-AMBIENT

RESISTANCE

BOARD-TO-AMBIENT

RESISTANCE

JUNCTION-TO-CASE

(BOTTOM) RESISTANCE

JUNCTION AMBIENT

CASE (BOTTOM)-TO-BOARD

RESISTANCE

LTM8055

8055f

For more information www.linear.com/LTM8055

Typical applicaTions

12VOUT Fan Power from 3VIN to 36VIN with Analog

Current Control and 2A Input Current Limiting

Maximum Output Current

vs CTL Voltage

Output Voltage vs Output Current

24VOUT from 7VIN to 36VIN with 2.1A Accurate Current Limit

VIN

SVIN

IIN

GNDMODELL

LTM8055

IOUT

0.027Ω

VOUT

CLKOUT

IINMON

IOUTMON

RUN

COMP

SYNC

CTL

5.23k

8055 TA03a

22µF

25V

33µF

35V

VOUT

24V

10µF

50V

VIN

7V TO 36V

36.5k

600kHz

100k

CTL VOLTAGE (V)

OUTPUT CURRENT (A)

1.2

0.8

0.6

0.4

0.2

1.0

8055 TA02b

0.6 0.8 10 0.2 0.4 1.2

12VIN

VIN SVIN

IIN

GNDMODELL

FAN CONTROL

LTM8055

IOUT

0.05Ω

VOUT

CLKOUT

IINMON

IOUTMON

RUN

COMP

SYNC

CTL

0.022Ω

11.0k

100k

8055 TA02a

22µF

25V

VOUT

12V MAX

FAN

10µF

50V

VIN

3V TO 36V

1µF

50V

36.5k

600kHz

0.2V TO 1.2V

CONTROL RANGE

DAC

68µF

25V

OUTPUT CURRENT (A)

OUTPUT VOLTAGE (V)

8055 TA03b

1.5 20 0.5 1 2.5

12VIN

LTM8055

8055f

For more information www.linear.com/LTM8055

3.3VOUT from 9VIN to 24VIN with 5A Accurate Current Limit and

Output Current Monitor

Typical applicaTions

Tw o LTM8055s Paralleled to Get More Output Current. The Tw o µModules Are

Synchronized and Switching 180° Out Of Phase

VIN

SVIN

IIN

GNDMODELL

LTM8055

IOUT

0.011Ω

VOUT

CLKOUT

IINMON

IOUTMON

RUN

CTL

SYNC

COMP

56.2k 8055 TA04a

22µF

6.3V

100µF

6.3V

VOUT

3.3V

OUTPUT

CURRENT

MONITOR

10µF

50V

VIN

9V TO 24V

36.5k

600kHz

100k +

OUTPUT CURRENT (A)

OUTPUT VOLTAGE (V)

4.0

3.0

2.5

2.0

1.0

0.5

1.5

3.5

8055 TA04b

4 50 1 32 6

Output Voltage vs Output Current

VIN

SVIN

IIN

GNDMODELL

LTM8055

(MASTER) IOUT

0.008Ω

VOUT

IINMON

IOUTMON

RUN

CTL

SYNC

COMP

CLKOUT

22µF

25V

68µF

25V

VOUT

12V

10µF

50V

47pF

VIN

7V TO 36V

36.5k

600kHz

VIN

SVIN

IIN

GND

LTM8055

(SLAVE) IOUT

0.008Ω

VOUT

CTL

CLKOUT

IINMON

IOUTMON

RUN

COMP

SYNC

11k

100k

9.31k

8055 TA05a

10µF

50V

36.5k

600kHz

MODELL

100k

22µF

25V 68µF

25V

–

LT1636

IOUTMON Voltage vs Output Current

for Each Channel, 12VIN

COMBINED CURRENTS OF BOTH CHANNELS (A)

VIOUTMON (V)

1.2

0.8

0.6

0.4

0.2

1.0

8055 TA05b

100 5 15

MASTER

SLAVE

LTM8055

8055f

For more information www.linear.com/LTM8055

Typical applicaTions

Tw o LTM8055s Powered from Different Input Sources to Run a Single Load. Each LTM8055 Draws No More Than 1.8A from Its

Respective Power Source, and Are Synchronized 180° Out Of Phase with Each Other

Input Current and Output Voltage vs

Output Current 12VIN

VIN

SVIN

IIN

GNDLL MODE

LTM8055

IOUT

VOUT

IINMON

IOUTMON

RUN

CTL

SYNC

COMP

CLKOUT

22µF

25V

3A MAX

VOUT

12V

68µF

35V

10µF

50V

SUPPLY 1

6V TO 36VIN

SUPPLY 2

6V TO 36VIN

36.5k

600kHz

VIN

0.025Ω

SVIN

IIN

GNDLL

LTM8055

IOUT

VOUT

CLKOUT

IINMON

IOUTMON

RUN

CTL

SYNC

COMP

11k

8055 TA06a

22µF

25V

10µF

50V

36.5k

600kHz

47pF

MODE

100k

11k

100k

OUTPUT CURRENT (A)

INPUT CURRENT (A)

VOUT (V)

2.5

1.5

1.0

0.5

2.0

8055 TA06b

2 30 1 4

VOUT

INPUT CURRENT,

REGULATOR 1

INPUT CURRENT,

REGULATOR 2

LTM8055

8055f

For more information www.linear.com/LTM8055

package DescripTion

package phoTo

Table 4. LTM8055 Pin Assignment (Arranged by Pin Number)

PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION

A1 VOUT B1 VOUT C1 VOUT D1 IOUT E1 GND F1 LL

A2 VOUT B2 VOUT C2 VOUT D2 GND E2 GND F2 GND

A3 VOUT B3 VOUT C3 VOUT D3 GND E3 GND F3 GND

A4 VOUT B4 VOUT C4 VOUT D4 GND E4 GND F4 GND

A5 VOUT B5 VOUT C5 VOUT D5 GND E5 GND F5 GND

A6 VOUT B6 VOUT C6 VOUT D6 GND E6 GND F6 GND

A7 GND B7 GND C7 GND D7 GND E7 GND F7 GND

A8 GND B8 GND C8 GND D8 GND E8 GND F8 GND

A9 GND B9 GND C9 GND D9 GND E9 GND F9 GND

A10 GND B10 GND C10 GND D10 GND E10 GND F10 SVIN

A11 GND B11 GND C11 GND D11 GND E11 GND F11 SVIN

PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION

G1 CLKOUT H1 RT J1 FB K1 SS L1 GND

G2 MODE H2 SYNC J2 COMP K2 CTL L2 IOUTMON

G3 GND H3 GND J3 GND K3 GND L3 IINMON

G4 GND H4 GND J4 GND K4 GND L4 RUN

G5 GND H5 GND J5 GND K5 GND L5 GND

G6 GND H6 GND J6 GND K6 GND L6 GND

G7 GND H7 GND J7 GND K7 GND L7 GND

G8 GND H8 GND J8 GND K8 GND L8 GND

G9GND H9 GND J9 GND K9 GND L9 IIN

G10 VIN H10 VIN J10 VIN K10 VIN L10 VIN

G11 VIN H11 VIN J11 VIN K11 VIN L11 VIN

LTM8055

8055f

For more information www.linear.com/LTM8055

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

package DescripTion

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

PACKAGE TOP VIEW

PIN “A1”

CORNER

aaa Z

DETAIL A

PACKAGE BOTTOM VIEW

SEE NOTES

123891011 4567

PIN 1

BGA Package

121-Lead (15.00mm × 15.00mm × 4.92mm)

(Reference LTC DWG# 05-08-1891 Rev A)

NOTES:

1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994

2. ALL DIMENSIONS ARE IN MILLIMETERS

BALL DESIGNATION PER JESD MS-028 AND JEP95

5. PRIMARY DATUM -Z- IS SEATING PLANE

6. SOLDER BALL COMPOSITION CAN BE 96.5% Sn/3.0% Ag/0.5% Cu

OR Sn Pb EUTECTIC

DETAILS OF PIN #1 IDENTIFIER ARE OPTIONAL,

BUT MUST BE LOCATED WITHIN THE ZONE INDICATED.

THE PIN #1 IDENTIFIER MAY BE EITHER A MOLD OR

MARKED FEATURE

DETAIL A

Øb (121 PLACES)

DETAIL B

SUBSTRATE

ccc Z

DETAIL B

PACKAGE SIDE VIEW

MOLD

CAP

MX YZddd

MZeee

SYMBOL

aaa

bbb

ccc

ddd

eee

MIN

4.72

0.50

4.22

0.71

0.610

0.27

3.95

NOM

4.92

0.60

4.32

0.78

0.635

15.00

1.27

12.70

0.32

4.00

MAX

5.12

0.70

4.42

0.85

0.660

0.37

4.05

0.15

0.10

0.20

0.30

0.15

NOTES

DIMENSIONS

TOTAL NUMBER OF BALLS: 121

SUGGESTED PCB LAYOUT

TOP VIEW

0.000

3.810

5.080

3.810

6.350

5.080

6.350

2.540

1.270

2.540

1.270

6.350

5.080

1.270

6.350

5.080

3.810

2.540

1.270

0.3175

3.810

2.540

0.000

// bbb Z

0.635 ±0.025 Ø 121x

LTMXXXXXX

µModule

BGA 121 1112 REV A

TRAY PIN 1

BEVEL PACKAGE IN TRAY LOADING ORIENTATION

COMPONENT

PIN “A1”

7 PACKAGE ROW AND COLUMN LABELING MAY VARY

AMONG µModule PRODUCTS. REVIEW EACH PACKAGE

LAYOUT CAREFULLY

SEE NOTES

LTM8055

8055f

For more information www.linear.com/LTM8055

 LINEAR TECHNOLOGY CORPORATION 2015

LT 0215 • PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTM8055

Design resources

SUBJECT DESCRIPTION

µModule Design and Manufacturing Resources Design:

• Selector Guides

• Demo Boards and Gerber Files

• Free Simulation Tools

Manufacturing:

• Quick Start Guide/Demo Manual

• PCB Design, Assembly and Manufacturing Guidelines

• Package and Board Level Reliability

µModule Regulator Products Search 1. Sort table of products by parameters and download the result as a spread sheet.

2. Search using the Quick Power Search parametric table.

TechClip Videos Quick videos detailing how to bench test electrical and thermal performance of µModule products.

Digital Power System Management Linear Technology’s family of digital power supply management ICs are highly integrated solutions that

offer essential functions, including power supply monitoring, supervision, margining and sequencing,

and feature EEPROM for storing user configurations and fault logging.

relaTeD parTs

Typical applicaTion

PART NUMBER DESCRIPTION COMMENTS

LTM4605 Higher Power Buck-Boost (Up to 60W) External Inductor, Synchronous Switching Buck-Boost; Up to 36VIN, 0.8V ≤ VOUT

≤ 16V

LTM4607 Higher Power Buck-Boost (Up to 60W) External Inductor, Synchronous Switching Buck-Boost; Up to 36VIN, 0.8V ≤ VOUT

≤ 24V

LTM4609 Higher Power Buck-Boost (Up to 60W) External Inductor, Synchronous Switching Buck-Boost; Up to 36VIN, 0.8V ≤ VOUT

≤ 34V

LTM8045 Smaller, Lower Power SEPIC and Inverting; 700mA, 6.25mm × 11.25mm × 4.92mm BGA

LTM8046 Isolated, Lower Power Flyback Topology, 550mA (5VOUT, 24VIN), UL60950, 2kVAC

14.4V, 3A Lead-Acid Battery Charger Input Current Limited to 2.1A Input Current vs Input Voltage,

IOUT = 3A

VIN SVIN

IIN

GNDLL MODE

LTM8055

IOUT

0.02Ω

VOUT

CLKOUT

IINMON

IOUTMON

RUN

CTL

SYNC

COMP

0.022Ω

9.09k

100k

8055 TA07a

22µF

25V

47µF

25V

VOUT

14.4V

10µF

50V

VIN

3V TO 36V

36.5k

600kHz

1µF

50V

INPUT VOLTAGE (V)

INPUT CURRENT (A)

2.5

2.0

1.5

0.5

1.0

8055 TA07b

300 2010 40