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LTM8031

8031fb

Typical applicaTion

DescripTion

Ultralow Noise EMC 36V, 1A

DC/DC µModule Regulator

The LTM

8031 is an electromagnetic compatible (EMC)

36V, 1A DC/DC µModule

buck converter designed to

meet the radiated emissions requirements of EN55022.

Conducted emission requirements can be met by adding

standard ﬁlter components. Included in the package are the

switching controller, power switches, inductor, ﬁlters and

all support components. Operating over an input voltage

range of 3.6V to 36V, the LTM8031 supports an output

voltage range of 0.8V to 10V, and a switching frequency

range of 200kHz to 2.4MHz, each set by a single resistor.

Only the bulk input and output ﬁlter capacitors are needed

to ﬁnish the design. The low proﬁle package (2.82mm)

enables utilization of unused space on the bottom of PC

boards for high density point of load regulation.

The LTM8031 is packaged in a thermally enhanced, compact

(9mm ×15mm) and low proﬁle (2.82mm) overmolded land

grid array (LGA) package suitable for automated assembly

by standard surface mount equipment. The LTM8031 is

RoHS compliant.

Ultralow Noise 5V/1A DC/DC µModule Regulator

FeaTures

applicaTions

n Complete Step-Down Switch Mode Power Supply

n Wide Input Voltage Range: 3.6V to 36V

n 1A Output Current

n 0.8V to 10V Output Voltage

n Switching Frequency from 200kHz to 2.4MHz

n EN55022 Class B Compliant with Margin

n Current Mode Control

n (e4) RoHS Compliant Package with Gold Pad Finish

n Programmable Soft-Start

n Pin Compatible with the LTM8032

n Low Proﬁle (9mm × 15mm × 2.82mm)

Surface Mount LGA Package

n Automotive Battery Regulation

n Power for Portable Products

n Distributed Supply Regulation

n Industrial Supplies

n Wall Transformer Regulation

LTM8031 EMI Performance

L, LT, LTC, LTM, µModule, Burst Mode, Linear Technology and the Linear logo are registered

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

respective owners.

47.5k44.2k

*RUNNING VOLTAGE RANGE.

SEE APPLICATIONS FOR START-UP DETAILS

VIN

FIN

1µF

10µF

VOUT

RUN/SS

VIN*

7VDC TO 36VDC

PGOOD

BIAS

LTM8031

AUX

OUT

SYNC GND

8031 TA01a

ADJ

FREQUENCY (MHz)

EMISSIONS LEVEL (dBµV/m)

800

8031 TA01b

EN55022

CLASS B

LIMIT

–10 200100 400300 600 700 900

500 1000

VIN = 36V

LTM8031

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VIN, FIN, RUN/SS Voltage ..........................................40V

ADJ, RT, SHARE Voltage .............................................5V

VOUT, AUX .................................................................10V

Current from AUX ................................................100mA

PGOOD, SYNC ..........................................................30V

BIAS .......................................................................... 25V

VIN + BIAS ................................................................. 56V

Maximum Junction Temperature (Note 2)............. 125°C

Solder Temperature (Note 3) ................................. 245°C

(Note 1)

GND

BANK 1

BANK 2

BANK 3

234

TOP VIEW

LGA PACKAGE

71-LEAD (9mm × 15mm × 2.82mm)

567

VOUT

VIN

ADJ

PGOOD

SYNCRUN/SS

FIN

BIAS AUX

TJMAX = 125°C, θJA = 20.7°C/W, θJC(BOTTOM) = 8.4°C/W,

θJC(TOP) = 25.6°C/W, θJBOARD = 13.8°C/W

θ VALUES DETERMINED PER JESD 51-9

WEIGHT = 1.2g

pin conFiguraTionabsoluTe MaxiMuM raTings

LEAD FREE FINISH TRAY PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTM8031EV#PBF LTM8031EV#PBF LTM8031V 71-Lead (9mm × 15mm × 2.82mm) LGA –40°C to 125°C

LTM8031IV#PBF LTM8031IV#PBF LTM8031V 71-Lead (9mm × 15mm × 2.82mm) LGA –40°C to 125°C

LTM8031MPV#PBF LTM8031MPV#PBF LTM8031V 71-Lead (9mm × 15mm × 2.82mm) LGA –55°C to 125°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

This product is only offered in trays. For more information go to: http://www.linear.com/packaging/

orDer inForMaTion

LTM8031

8031fb

elecTrical characTerisTics

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 LTM8031E is guaranteed to meet performance speciﬁcations

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

internal temperature range are assured by design, characterization and

correlation with statistical process controls. The LTM8031I is guaranteed

The l denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBIAS = 3V, unless otherwise speciﬁed.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VIN Input DC Voltage l3.6 36 V

VOUT Output DC Voltage 0.2A < IOUT ≤ 1A, RADJ Open

0.2A < IOUT ≤ 1A, RADJ = 21.6k

0.8

IOUT Continuous Output DC Current VIN = 24V 1 A

IQ(VIN) VIN Quiescent Current VRUN/SS = 0.2V

VBIAS = 3V, Not Switching

VBIAS = 0V, Not Switching

0.6

120

µA

IQ(BIAS) BIAS Quiescent Current VRUN/SS = 0.2V

VBIAS = 3V, Not Switching

VBIAS = 0V, Not Switching

0.03

120

µA

∆VOUT

VOUT

Line Regulation 10V ≤ VIN ≤ 36V, IOUT = 1A, VOUT = 3.3V 0.1 %

Load Regulation VIN = 24V, 0.2A ≤ IOUT ≤ 1A, VOUT = 3.3V 0.3 %

VOUT(AC_RMS) Output Ripple (RMS) VIN = 24V, IOUT = 1A, VOUT = 3.3V 6 mV

fSW Switching Frequency RT = 113k 325 kHz

VADJ Voltage at ADJ Pin l765 790 815 mV

VBIAS(MIN) Minimum BIAS Voltage for Proper Operation 1.9 2.8 V

IADJ Current Out of ADJ Pin VRUN/SS = 0V, VADJ = 0V, VOUT = 1V 4 µA

IRUN/SS RUN/SS Pin Current VRUN/SS = 2.5V 5 10 µA

VIH(RUN/SS) RUN/SS Input High Voltage 2.5 V

VIL(RUN/SS) RUN/SS Input Low Voltage 0.2 V

VPG(TH) ADJ Voltage Threshold for PGOOD to Switch 730 mV

IPGO PGOOD Leakage VPG = 30V 0.1 1 µA

IPGSINK PGOOD Sink Current VPG = 0.4V 200 800 µA

VSYNCIL SYNC Input Low Threshold fSYNC = 550kHz 0.5 V

VSYNCIH SYNC Input High Threshold fSYNC = 550kHz 0.7 V

ISYNC(BIAS) SYNC Pin Bias Current VSYNC = 0V, VBIAS = 0V 0.1 µA

VIN(RIPPLE) 550kHz Narrowband Conducted Emission

1MHz Narrowband Conducted Emission

3MHz Narrowband Conducted Emission

VIN = 24V, VOUT = 3.3V, IOUT = 1A, fSW = 550kHz,

5µH LISN

dBµV

to meet speciﬁcations over the full –40°C to 125°C internal operating

temperature range. The LTM8031MP 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: See Linear Technology Application Note 100.

LTM8031

8031fb

Typical perForMance characTerisTics

Input Current vs Output Current,

3.3VOUT

Input Current vs Output Current,

5VOUT

Input Current vs Output Current,

8VOUT

Minimum VIN vs Output Current

2.5V VOUT

3.3VOUT Efﬁciency 5VOUT Efﬁciency 8VOUT Efﬁciency

TA = 25°C, unless otherwise noted.

Minimum VIN vs Output Current

3.3V VOUT

Minimum VIN vs Output Current

5V VOUT

OUTPUT CURRENT (mA)

EFFICIENCY (%)

100

200 400 600 800

8031 G01

1000

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (mA)

EFFICIENCY (%)

100

200 400 600 800

8031 G02

1000

12VIN

24VIN

36VIN

OUTPUT CURRENT (mA)

EFFICIENCY (%)

100

200 400 600 800

8031 G03

1000

12VIN

24VIN

36VIN

OUTPUT CURRENT (mA)

INPUT CURRENT (mA)

300

400

500

600 1000

8031 G04

200

100

0200 400 800

600

700

800

5VIN

12VIN

24VIN

36VIN

OUTPUT CURRENT (mA)

INPUT CURRENT (mA)

300

400

500

800

8031 G05

200

100

250

350

450

150

0200 400 600 1000

12VIN

24VIN

36VIN

OUTPUT CURRENT (mA)

INPUT CURRENT (mA)

300

400

500

600 1000

8031 G06

200

100

0200 400 800

600

700

800

12VIN

24VIN

36VIN

OUTPUT CURRENT (mA)

(V)

4.0

4.2

4.4

600 1000

8031 G07

3.8

3.6

3.4 200 400 800

4.6

4.8

5.0

RUN/SS = VIN OR TOGGLED

RUNNING

OUTPUT CURRENT (mA)

(V)

5.1

5.6

6.1

800

8031 G08

4.6

4.1

3.6 200 400 600 1000

RUN/SS TOGGLED

RUN/SS = VIN

RUNNING

OUTPUT CURRENT (mA)

(V)

5.1

5.6

6.1

600 1000

8031 G09

4.6

4.1

3.6 200 400 800

6.6

7.1

7.6

RUN/SS = VIN

RUNNING OR RUN/SS TOGGLED

LTM8031

8031fb

Typical perForMance characTerisTics

Output Current vs Input Voltage

(Output Shorted)

Input Current vs Input Voltage

(Output Shorted)

Temperature Rise vs

Load Current, VOUT = 3.3V

Temperature Rise vs

Load Current, VOUT = 5V

Temperature Rise vs

Load Current, VOUT = 8V

Minimum VIN vs Output Current

8V VOUT

Minimum Input Running Voltage

vs Output Voltage, IOUT = 1A Bias Current vs Output Current

TA = 25°C, unless otherwise noted.

Temperature Rise vs

Load Current, VOUT = 10V

OUTPUT CURRENT (mA)

(V)

600 1000

8031 G10

4200 400 800

RUN/SS = VIN

RUNNING OR RUN/SS TOGGLED

VOUT (V)

VIN (V)

610

8031 G11

02 4 8

OUTPUT CURRENT (mA)

800

8031 G12

200 400 600 1000

BIAS CURRENT (mA)

8VOUT

5VOUT

3.3VOUT

VIN (V)

OUTPUT CURRENT (A)

2.55

2.60

2.65

8031 G13

2.50

2.45

2.35 816 24

4 36

12 20 28

2.40

2.75

2.70

VIN (V)

0.8

1.0

1.4

8031 G14

0.6

0.4

10 20 40

0.2

1.2

INPUT CURRENT (A)

OUTPUT CURRENT (mA)

TEMPERATURE RISE (°C)

200 400 600 800

8031 G15

1000

36VIN

24VIN

12VIN

5VIN

OUTPUT CURRENT (mA)

TEMPERATURE RISE (°C)

200 400 600 800

8031 G16

1000

36VIN

24VIN

12VIN

OUTPUT CURRENT (mA)

TEMPERATURE RISE (°C)

200 400 600 800

8031 G17

1000

36VIN

24VIN

12VIN

OUTPUT CURRENT (mA)

TEMPERATURE RISE (°C)

200 400 600 800

8031 G18

1000

36VIN

24VIN

LTM8031

8031fb

Typical perForMance characTerisTics

Radiated Emissions Radiated Emissions

TA = 25°C, unless otherwise noted.

pin FuncTions

VIN (Bank 3): The VIN pin supplies current to the LTM8031’s

internal regulator and to the internal power switch. This

pin must be locally bypassed with an external, low ESR

capacitor of at least 1µF .

FIN (K3, L3): Filtered Input. This is the node after the input

EMI ﬁlter. Use this only if there is a need to modify the

behavior of the integrated EMI ﬁlter or if VIN rises or falls

rapidly; otherwise, leave these pins unconnected. See the

Applications Information section for more details.

GND (Bank 2): Tie these GND pins to a local ground plane

below the LTM8031 and the circuit components. Return

the feedback divider (RADJ) to this net.

VOUT (Bank 1): Power Output Pins. Apply the output ﬁlter

capacitor and the output load between these pins and

GND pins.

AUX (Pin H5): Low Current Voltage Source for BIAS. In

many designs, the BIAS pin is simply connected to VOUT

The AUX pin is internally connected to VOUT and is placed

adjacent to the BIAS pin to ease printed circuit board rout-

ing. Although this pin is internally connected to VOUT

, do

not connect this pin to the load. If this pin is not tied to

BIAS, leave it ﬂoating.

BIAS (Pin H4): The BIAS pin connects to the internal power

bus. Connect to a power source greater than 2.8V. If the

output is greater than 2.8V, connect this pin to AUX. If the

output voltage is less, connect this to a voltage source

between 2.8V and 25V. Also, make sure that BIAS + VIN

is less than 56V.

RUN/SS (Pin L5): Pull RUN/SS pin to less than 0.2V to

shut down the LTM8031. Tie to 2.5V or more for normal

operation. If the shutdown feature is not used, tie this pin

to the VIN pin. RUN/SS also provides a soft-start function;

see the Applications Information section.

RT (Pin G7): The RT pin is used to program the switching

frequency of the LTM8031 by connecting a resistor from

this pin to ground. 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.

SHARE (Pin H7): Tie this to the SHARE pin of another

LTM8031 when paralleling the outputs.

FREQUENCY (MHz)

EMISSIONS LEVEL (dBµV/m)

90 VIN = 36V

VOUT = 10V AT 1A

800

8031 G19

–10 200100 400300 600 700 900

500 1000

EN55022

CLASS B

LIMIT

FREQUENCY (MHz)

EMISSIONS LEVEL (dBµV/m)

90 VIN = 36V

VOUT = 2.5V AT 1A

800

8031 G20

–10 200100 400300 600 700 900

500 1000

EN55022

CLASS B

LIMIT

LTM8031

8031fb

pin FuncTions

SYNC (Pin L6): This is the external clock synchronization

input. Ground this pin for low ripple Burst Mode

operation

at low output loads. Tie to a stable voltage source greater

than 0.7V to disable Burst Mode operation. Do not leave

this pin ﬂoating. Tie to a clock source for synchroniza-

tion. Clock edges should have rise and fall times faster

than 1µs. See Synchronization section in Applications

Information.

PGOOD (Pin K7): The PGOOD pin is the open-collector

output of an internal comparator. PGOOD remains low until

the ADJ pin is within 10% of the ﬁnal regulation voltage.

The PGOOD output is valid when VIN is above 3.6V and

RUN/SS is high. If this function is not used, leave this

pin ﬂoating.

ADJ (Pin J7): The LTM8031 regulates its ADJ pin to 0.79V.

Connect the adjust resistor from this pin to ground. The

value of RADJ is given by the equation:

RADJ =196.71

VOUT – 0.79

where RADJ is in kΩ.

block DiagraM

CURRENT

MODE

CONTROLLER

249k 10µF

VOUT

AUX

GND

4.7µH

BIAS

22pF

EMI FILTER

FIN

VIN

GND

SYNC RT PGOOD ADJ

8031 BD

RUN/SS

LTM8031

8031fb

operaTion

applicaTions inForMaTion

The LTM8031 is a standalone nonisolated step-down

switching DC/DC power supply. It can deliver up to 1A of

DC output current with only bulk external input and output

capacitors. This module provides a precisely regulated

output voltage programmable via one external resistor

from 0.8VDC to 10VDC. The input voltage range is 3.6V

to 36V. Given that the LTM8031 is a step-down converter,

make sure that the input voltage is high enough to support

the desired output voltage and load current. A simpliﬁed

Block Diagram is given on the previous page.

The LTM8031 is designed with an input EMI ﬁlter and other

features to make its radiated emissions compliant with

several EMC speciﬁcations including EN55022 class B.

Compliance with conducted emissions requirements may

be obtained by adding a standard input ﬁlter.

The LTM8031 contains a current mode controller, power

switching element, power inductor, power Schottky diode

and a modest amount of input and output capacitance. The

LTM8031 is a ﬁxed frequency PWM regulator. The switch-

ing frequency is set by simply connecting the appropriate

resistor value from the RT pin to GND.

An internal regulator provides power to the control circuitry.

The bias regulator can draw power from the VIN pin, but if

the BIAS pin is connected to an external voltage higher than

2.8V, bias power will be drawn from the external source

(typically the regulated output voltage). This improves

efﬁciency. The RUN/SS pin is used to place the LTM8031

in shutdown, disconnecting the output and reducing the

input current to less than 1µA.

To further optimize efﬁciency, the LTM8031 automatically

switches to Burst Mode operation in light load situations.

Between bursts, all circuitry associated with controlling the

output switch is shut down reducing the input supply cur-

rent to 50µA in a typical application. The oscillator reduces

the LTM8031’s operating frequency when the voltage at the

ADJ pin is low. This frequency foldback helps to control

the output current during start-up and overload.

The LTM8031 contains a power good comparator which

trips when the ADJ pin is at 90% of its regulated value.

The PGOOD output is an open-collector transistor that is

off when the output is in regulation, allowing an external

resistor to pull the PGOOD pin high. Power good is valid

when the LTM8031 is enabled and VIN is above 3.6V.

For most applications, the design process is straight

forward, 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, RADJ and RT

values.

3. Connect BIAS as indicated.

As the integrated input EMI ﬁlter may ring in response to an

application of a step input voltage, a bulk capacitance, series

resistance or some clamping mechanism may be required.

See the Hot-Plugging Safely section for details.

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.

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 applied

voltage and give dependable service. Other types, includ-

ing Y5V and Z5U have very large temperature and voltage

coefﬁcients of capacitance. In an application circuit they

LTM8031

8031fb

applicaTions inForMaTion

Table 1. Recommended Component Values and Conﬁguration (See Typical Performance Characteristics for Load Conditions)

VIN VOUT CIN COUT RADJ BIAS fOPTIMAL RT(OPTIMAL) fMAX RT(MIN)

3.6V to 36V 0.82V 1µF 0805 50V 2 × 100µF 1206 6.3V 5.11M ≥2.8V, <25V 250kHz 150k 250kHz 150k

3.6V to 36V 1.20V 1µF 0805 50V 100µF//47µF 1206 6.3V 475k ≥2.8V, <25V 300kHz 124k 325kHz 113k

3.6V to 36V 1.80V 1µF 0805 50V 100µF 1206 191k ≥2.8V, <25V 420kHz 84.5k 450kHz 78.7k

3.6V to 36V 2.00V 1µF 0805 50V 100µF 1206 162k ≥2.8V, <25V 450kHz 78.7k 475kHz 73.2k

3.6V to 36V 2.50V 1µF 0805 50V 47µF 0805 6.3V 115k ≥2.8V, <25V 550kHz 61.9k 575kHz 59.0k

4.75V to 36V 3.30V 1µF 0805 50V 22µF 1206 6.3V 78.7k AUX 675kHz 48.7k 725kHz 44.2k

6.8V to 36V 5.00V 1µF 0805 50V 10µF 1206 6.3V 46.4k AUX 975kHz 29.4k 1000kHz 28.0k

10.5V to 36V 8.00V 1µF 0805 50V 4.7µF 1206 10V 26.7k AUX 1200kHz 23.7k 1600kHz 15.8k

13V to 36V 10.00V 1µF 0805 50V 4.7µF 0805 16V 21.0k AUX 1250kHz 22.6k 2050kHz 10.5k

3.6V to 15V 0.82V 1µF 0805 50V 2 × 100µF 1206 6.3V 5.11M VIN 500kHz 69.8k 600kHz 56.2k

3.6V to 15V 1.20V 1µF 0805 50V 100µF 1206 6.3V 475k VIN 600kHz 56.2k 750kHz 42.2k

3.6V to 15V 1.80V 1µF 0805 50V 100µF 1206 191k VIN 650kHz 51.1k 1000kHz 28.0k

3.6V to 15V 2.00V 1µF 0805 50V 100µF 1206 162k VIN 650kHz 51.1k 1100kHz 26.7k

3.6V to 15V 2.50V 1µF 0805 50V 47µF 0805 6.3V 115k VIN 700kHz 47.5k 1350kHz 20.5k

4.75V to 15V 3.30V 1µF 0805 50V 22µF 1206 6.3V 78.7k AUX 950kHz 32.4k 1650kHz 15.0k

6.8V to 15V 5.00V 1µF 0805 50V 10µF 1206 6.3V 46.4k AUX 1150kHz 25.5k 2400kHz 7.87k

10.5V to 15V 8.00V 1µF 0805 50V 4.7µF 1206 10V 26.7k AUX 1200kHz 23.7k 2400kHz 7.87k

9V to 24V 0.82V 1µF 0805 50V 2 × 100µF 1206 6.3V 5.11M ≥2.8V, <25V 350kHz 105k 375kHz 93.1k

9V to 24V 1.20V 1µF 0805 50V 100µF//47µF 1206 6.3V 475k ≥2.8V, <25V 450kHz 78.7k 475kHz 73.2k

9V to 24V 1.80V 1µF 0805 50V 100µF 1206 191k ≥2.8V, <25V 600kHz 56.2k 650kHz 51.1k

9V to 24V 2.00V 1µF 0805 50V 100µF 1206 162k ≥2.8V, <25V 650kHz 51.1k 700kHz 47.5k

9V to 24V 2.50V 1µF 0805 50V 47µF 0805 6.3V 115k ≥2.8V, <25V 700kHz 47.5k 850kHz 37.4k

9V to 24V 3.30V 1µF 0805 50V 22µF 1206 6.3V 78.7k AUX 950kHz 32.4k 1050kHz 28.0k

9V to 24V 5.00V 1µF 0805 50V 10µF 1206 6.3V 46.4k AUX 1150kHz 25.5k 1550kHz 16.5k

10.5V to 24V 8.00V 1µF 0805 50V 4.7µF 1206 10V 26.7k AUX 1200kHz 23.7k 2400kHz 7.87k

13V to 24V 10.00V 1µF 0805 50V 4.7µF 0805 16V 21.0k AUX 1250kHz 22.6k 2400kHz 7.87k

Note: An input bulk capacitor is required.

LTM8031

8031fb

applicaTions inForMaTion

may have only a small fraction of their nominal capaci-

tance resulting in much higher output voltage ripple than

expected. Ceramic capacitors are also piezoelectric. In

Burst Mode operation, the LTM8031’s switching frequency

depends on the load current, and can excite a ceramic

capacitor at audio frequencies, generating audible noise.

Since the LTM8031 operates at a lower current limit during

Burst Mode operation, the noise is typically very quiet to a

casual ear. If this audible noise is unacceptable, use a high

performance electrolytic capacitor at the output. The input

capacitor can be a parallel combination of a 1µF ceramic

capacitor and a low cost electrolytic capacitor.

A ﬁnal precaution regarding ceramic capacitors concerns

the maximum input voltage rating of the LTM8031. A

ceramic input capacitor combined with trace or cable

inductance forms a high Q (under damped) tank circuit.

If the LTM8031 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.

Electromagnetic Compliance

The LTM8031 is compliant with the radiated emissions

requirements of EN55022 class B. Graphs of the LTM8031’s

EMC performance are given in the Typical Performance

Characteristics section. Further data, operating conditions

and test setup are detailed in an EMI Test report available

from Linear Technology.

Frequency Selection

The LTM8031 uses a constant frequency PWM architecture

that can be programmed to switch from 200kHz to 2.4MHz

by using a resistor tied from the RT pin to ground. Table 2

provides a list of RT resistor values and their resultant

frequencies.

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

LTM8031 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

LTM8031 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 or unnecessarily large output

capacitor. The maximum frequency (and attendant RT value)

at which the LTM8031 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.

Table 2. Switching Frequency vs RT Value

SWITCHING FREQUENCY (MHz) RT VALUE (kΩ)

0.2 187

0.3 124

0.4 88.7

0.5 69.8

0.6 56.2

0.7 47.5

0.8 39.2

0.9 34

1.0 28.0

1.2 23.7

1.4 19.1

1.5 16.2

1.8 13.3

2 11.5

2.2 9.76

2.4 8.66

LTM8031

8031fb

applicaTions inForMaTion

BIAS Pin Considerations

The BIAS pin is used to provide drive power for the internal

power switching stage and operate internal circuitry. For

proper operation, it must be powered by at least 2.8V. If

the output voltage is programmed to be 2.8V or higher,

simply tie BIAS to AUX. If VOUT is less than 2.8V, BIAS

can be tied to VIN or some other voltage source. In all

cases, ensure that the maximum voltage at the BIAS pin

is both less than 25V and the sum of VIN and BIAS is less

than 56V. If BIAS power is applied from a remote or noisy

voltage source, it may be necessary to apply a decoupling

capacitor locally to the LTM8031.

Load Sharing

Two or more LTM8031s may be paralleled to produce higher

currents. This may, however, alter the EMI performance of

the LTM8031s. To do this, tie the VIN, ADJ, VOUT and SHARE

pins of all the paralleled LTM8031s together. To ensure that

paralleled modules start up together, the RUN/SS pins may

be tied together, as well. Synchronize the LTM8031s to an

external clock to eliminate beat frequencies, if required.

If the RUN/SS pins are not tied together, make sure that

the same valued soft-start capacitors are used for each

module. An example of two LTM8031 modules conﬁgured

for load sharing is given in the Typical Applications sec-

tion. For 2A applications also see the LTM8032, 2A EMC

DC/DC µModule regulator

Burst Mode Operation

To enhance efﬁciency at light loads, the LTM8031 auto-

matically switches to Burst Mode operation which keeps

the output capacitor charged to the proper voltage while

minimizing the input quiescent current. During Burst Mode

operation, the LTM8031 delivers single cycle bursts of

current to the output capacitor followed by sleep periods

where the output power is delivered to the load by the output

capacitor. In addition, VIN and BIAS quiescent currents are

reduced to typically 25µA and 60µA respectively during

the sleep time. As the load current decreases towards a

no-load condition, the percentage of time that the LTM8031

operates in sleep mode increases and the average input

current is greatly reduced, resulting in higher efﬁciency.

Burst Mode operation is enabled by tying SYNC to GND. To

disable Burst Mode operation, tie SYNC to a stable voltage

above 0.7V. Do not leave the SYNC pin ﬂoating.

Minimum Input Voltage

The LTM8031 is a step-down converter, so a minimum

amount of headroom is required to keep the output in regu-

lation. In addition, the input voltage required to turn on is

higher than that required to run, and depends upon whether

the RUN/SS is used. As shown in the Typical Performance

Characteristics section, it takes only about 3.6VIN for the

LTM8031 to run a 3.3V output at light load. If RUN/SS is

pulled up to VIN, it takes 5.7VIN to start. If the LTM8031

is enabled via the RUN/SS pin, the minimum voltage to

start at light loads is lower, about 4.4V. Similar curves for

2.5VOUT

, 5VOUT and 8VOUT operation are also provided in

the Typical Performance Characteristics section.

Soft-Start

The RUN/SS pin can be used to soft-start the LTM8031,

reducing the maximum input current during start-up. The

RUN/SS pin is driven through an external RC network to

create a voltage ramp at this pin. Figure 1 shows the start-

up and shutdown waveforms with the soft-start circuit. By

choosing an appropriate RC time constant, the peak start-up

current can be reduced to the current that is required to

regulate the output, with no overshoot. Choose the value

of the resistor so that it can supply at least 20µA when

the RUN/SS pin reaches 2.5V.

LTM8031

8031fb

Synchronization

The internal oscillator of the LTM8031 can be synchro-

nized by applying an external 250kHz to 2MHz clock to

the SYNC pin. Do not leave this pin ﬂoating. The resistor

tied from the RT pin to ground should be chosen such

that the LTM8031 oscillates 20% lower than the intended

synchronization frequency (see the Frequency Selection

section). The LTM8031 will not enter Burst Mode operation

while synchronized to an external clock, but will instead

skip pulses to maintain regulation.

Shorted Input Protection

Care needs to be taken in systems where the output will

be held high when the input to the LTM8031 is absent.

This may occur in battery charging applications or in

battery back-up systems where a battery or some other

supply is diode ORed with the LTM8031’s output. If the

VIN pin is allowed to ﬂoat and the RUN/SS pin is held high

(either by a logic signal or because it is tied to VIN), then

the LTM8031’s internal circuitry will pull its quiescent

current through its internal power switch. This is ﬁne if

your system can tolerate a few milliamps in this state. If

you ground the RUN/SS pin, the internal switch current

will drop to essentially zero. However, if the VIN pin is

grounded while the output is held high, then parasitic

diodes inside the LTM8031 can pull large currents from

the output through the VIN pin, potentially damaging the

applicaTions inForMaTion

Figure 2. The Input Diode Prevents a Shorted Input from

Discharging a Back-Up Battery Tied to the Output. It Also

Protects the Circuit from a Reversed Input. The LTM8031

Runs Only When the Input is Present

VOUT

VIN

RUN/SS

BIAS

ADJ

LTM8031

8031 F02

VOUT

GND

VIN

AUX

SYNC

device. Figure 2 shows a circuit that will run only when

the input voltage is present and that protects against a

shorted or reversed input.

PCB Layout

Most of the headaches associated with PCB layout have

been alleviated or even eliminated by the high level of

integration of the LTM8031. The LTM8031 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 3

for a suggested layout.

Ensure that the grounding and heat sinking are acceptable.

A few rules to keep in mind are:

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

their respective pins.

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

and GND connection of the LTM8031. If a capacitor

is connected to the FIN terminals, place it as close

as possible to the FIN terminals, such that its ground

connection is as close as possible to that of the CIN

capacitor.

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

VOUT and GND connection of the LTM8031.

8031 F01

0.5A/DIV

VRUN/SS

2V/DIV

VOUT

2V/DIV

RUN/SS

GND

0.22µF

RUN

15k

2ms/DIV

Figure 1. To Soft-Start the LTM8031, Add a Resistor

and Capacitor to the RUN/SS Pin

LTM8031

8031fb

applicaTions inForMaTion

4. Place the CIN and COUT capacitors such that their

ground currents ﬂow directly adjacent or underneath

the LTM8031.

5. 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 LTM8031.

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

internal ground plane. Liberally distribute these GND vias

to provide both a good ground connection and thermal

path to the internal planes of the printed circuit board.

Hot-Plugging Safely

The small size, robustness and low impedance of ceramic

capacitors make them an attractive option for the input

bypass capacitor of LTM8031. However, these capacitors

can cause problems if the LTM8031 is plugged into a live

or fast rising or falling 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 under-damped tank

circuit, and the voltage at the VIN pin of the LTM8031 can

ring to twice the nominal input voltage, possibly exceed-

ing the LTM8031’s rating and damaging the part. A similar

phenomenon can occur inside the LTM8031 module, at the

output of the integrated EMI ﬁlter, with the same potential

of damaging the part.

If the input supply is poorly controlled or the user will be

plugging the LTM8031 into an energized supply, the input

network should be designed to prevent this overshoot. Fig-

ure 4 shows the waveforms that result when an LTM8031

circuit is connected to a 24V supply through six feet of 24-

gauge twisted pair. The ﬁrst plot (4a) is the response with

a 2.2µF ceramic capacitor at the input. The input voltage

Figure 3. Layout Showing Suggested External Components,

GND Plane and Thermal Vias

GND

COUT

CIN

8031 F03

VIN

FIN

RUN/SS

SYNC

PGOOD

RADJ

AUX

BIAS

VOUT

GND

OPTIONAL

FIN

CAPACITOR

LTM8031

8031fb

applicaTions inForMaTion

rings as high as 35V and the input current peaks at 20A.

One method of damping the tank circuit is to add another

capacitor with a series resistor to the circuit, as shown

in Figure 4b. A 0.7Ω resistor is added in series with the

input to eliminate the voltage overshoot (it also reduces

the peak input current). A 0.1µF capacitor improves high

frequency ﬁltering. For high input voltages its impact on

efﬁciency is minor, reducing efﬁciency less than one-half

percent for a 5V output at full load operating from 24V.

By far the most popular method of controlling overshoot

is shown in Figure 4c, where an aluminum electrolytic

capacitor has been connected to FIN. This capacitor’s high

equivalent series resistance damps the circuit and elimi-

nates the voltage overshoot. The extra capacitor improves

low frequency ripple ﬁltering and can slightly improve the

efﬁciency of the circuit, though it is likely to be the largest

component in the circuit. Placing the electrolytic capacitor

at the FIN terminals can also improve the LTM8031’s EMI

ﬁltering as well as guard against overshoots caused by

the Q of the integrated ﬁlter.

Thermal Considerations

The LTM8031 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 Characteristics section

can be used as a guide. These curves were generated by a

LTM8031 mounted to a 35cm2 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 junction-to-air and junction-to-board thermal resis-

tances given in the Pin Conﬁguration diagram may also be

used to estimate the LTM8031 internal temperature. These

thermal coefﬁcients are determined per JESD 51-9 (JEDEC

standard, test boards for area array surface mount package

thermal measurements) through analysis and physical

correlation. Bear in mind that the actual thermal resistance

of the LTM8031 to the printed circuit board depends upon

the design of the circuit board. The die temperature of

the LTM8031 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 LTM8031.

The bulk of the heat ﬂow out of the LTM8031 is through the

bottom of the module and the LGA 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.

Finally, be aware that at high ambient temperatures the

internal Schottky diode will have signiﬁcant leakage current

increasing the quiescent current of the LTM8031.

LTM8031

8031fb

Typical applicaTions

Figure 4. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures

Reliable Operation When the LTM8031 is Hot-Plugged to a Live Supply

LTM8031

4.7µF

VIN

20V/DIV

IIN

10A/DIV

20µs/DIV

VIN

CLOSING SWITCH

SIMULATES HOT PLUG

IIN

(4a)

(4b)

LOW

IMPEDANCE

ENERGIZED

24V SUPPLY

STRAY

INDUCTANCE

DUE TO 6 FEET

(2 METERS) OF

TWISTED PAIR

LTM8031

4.7µF0.1µF

0.7Ω VIN

20V/DIV

IIN

10A/DIV

20µs/DIV

DANGER

RINGING VIN MAY EXCEED

ABSOLUTE MAXIMUM RATING

(4c)

4.7µF

22µF

35V

AI.EI.

8031 F04

VIN

20V/DIV

IIN

10A/DIV

20µs/DIV

VIN

LTM8031

VIN

FIN

LTM8031

8031fb

Typical applicaTions

0.82V Step-Down Converter

1.8V Step-Down Converter

191k

*RUNNING VOLTAGE RANGE.

SEE APPLICATIONS FOR START-UP DETAILS

56.2k

VIN

FIN

1µF 100µF

VOUT

1.8V

RUN/SS

VIN*

9V TO 24V

PGOOD

BIAS

LTM8031

AUX

OUT

SYNC GND

8031 TA03

ADJ

5.11M

*RUNNING VOLTAGE RANGE.

SEE APPLICATIONS FOR START-UP DETAILS

69.8k

VIN

FIN

1µF 200µF

VOUT

0.82V

RUN/SS

VIN*

3.6V TO 15V

PGOOD

BIAS

LTM8031

AUX

OUT

SYNC GND

8031 TA02

ADJ

LTM8031

8031fb

Typical applicaTions

2.5V Step-Down Converter

5V Step-Down Converter

115k

*RUNNING VOLTAGE RANGE.

SEE APPLICATIONS FOR START-UP DETAILS

61.9k

VIN

FIN

1µF 47µF

VOUT

2.5V

RUN/SS

VIN*

3.6V TO 36V

3.3V

PGOOD

BIAS

LTM8031

AUX

OUT

SYNC GND

8031 TA04

ADJ

VIN

FIN

1µF

10µF

46.4k29.4k

VOUT

RUN/SS

VIN*

6.8V TO 36V

PGOOD

BIAS

LTM8031

AUX

OUT

SYNC GND

8031 TA05

ADJ

*RUNNING VOLTAGE RANGE.

SEE APPLICATIONS FOR START-UP DETAILS

3.3V Step-Down Converter

VIN

FIN

1µF

22µF

78.7k48.7k

VOUT

3.3V

RUN/SS

VIN*

4.75V TO 36V

PGOOD

BIAS

LTM8031

AUX

OUT

SYNC GND

8031 TA08

ADJ

*RUNNING VOLTAGE RANGE.

SEE APPLICATIONS FOR START-UP DETAILS

LTM8031

8031fb

Typical applicaTions

package phoTograph

Two LTM8031s Operating in Parallel (Also See the LTM8032, 2A Pin Compatible)

VIN

FIN

1µF

13.7k23.7k

8031 TA07

10µF

VOUT

1.9A

RUN/SS

VIN*

11.5V TO 36V

OPTIONAL SYNC TIE TO

GND IF NOT USED

PGOOD

BIAS

LTM8031

AUX

OUT

SYNC GND ADJ

23.7k

VIN

FIN

1µF

RUN/SS

PGOOD

BIAS

LTM8031

AUX

OUT

SYNC GND ADJ

*RUNNING VOLTAGE RANGE.

SEE APPLICATIONS FOR START-UP DETAILS

LTM8031

8031fb

package DescripTion

LGA Package

71-Lead (15mm × 9mm × 2.82mm)

(Reference LTC DWG # 05-08-1823 Rev Ø)

9.00

BSC

PACKAGE TOP VIEW

LGA 71 0108 REV Ø

15.00

BSC

PAD 1

CORNER

PADS

SEE NOTES

aaa Z

2.670 – 2.970

DETAIL A

PACKAGE SIDE VIEW

DETAIL A

SUBSTRATE

MOLD

CAP

0.27 – 0.37

2.40 – 2.60

bbb Z

1.270

BSC

0.635 ±0.025 SQ. 71x

12.700

BSC

7.620

BSC

PAD 1

Ø (0.635)

PACKAGE IN TRAY LOADING ORIENTATION

2.540

1.270

5.080

6.350

3.810

0.000

1.270

3.810

2.540

1.270

0.000

SUGGESTED PCB LAYOUT

TOP VIEW

LTMXXXXXX

µModule

TRAY PIN 1

BEVEL

COMPONENT

PIN 1

PACKAGE BOTTOM VIEW

67 5 1234

NOTES:

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

2. ALL DIMENSIONS ARE IN MILLIMETERS

LAND DESIGNATION PER JESD MO-222, SPP-010 AND SPP-020

5. PRIMARY DATUM -Z- IS SEATING PLANE

6. THE TOTAL NUMBER OF PADS: 71

DETAILS OF PAD #1 IDENTIFIER ARE OPTIONAL,

BUT MUST BE LOCATED WITHIN THE ZONE INDICATED.

THE PAD #1 IDENTIFIER MAY BE EITHER A MOLD OR

MARKED FEATURE

DETAIL A

SYXeee

DETAIL A

SYMBOL

aaa

bbb

eee

TOLERANCE

0.15

0.10

0.05

1.27

BSC

LTM8031

8031fb

package DescripTion

PIN SIGNAL DESCRIPTION

A1 VOUT

A2 VOUT

A3 VOUT

A4 VOUT

A5 GND

A6 GND

A7 GND

B1 VOUT

B2 VOUT

B3 VOUT

B4 VOUT

B5 GND

B6 GND

B7 GND

C1 VOUT

C2 VOUT

C3 VOUT

C4 VOUT

C5 GND

C6 GND

C7 GND

D1 VOUT

D2 VOUT

D3 VOUT

D4 VOUT

D5 GND

D6 GND

D7 GND

E1 GND

E2 GND

E3 GND

E4 GND

E5 GND

E6 GND

E7 GND

PIN SIGNAL DESCRIPTION

F1 GND

F2 GND

F3 GND

F4 GND

F5 GND

F6 GND

F7 GND

G1 GND

G2 GND

G3 GND

G4 GND

G5 GND

G6 GND

G7 RT

H1 GND

H2 GND

H3 GND

H4 BIAS

H5 AUX

H6 GND

H7 SHARE

J5 GND

J6 GND

J7 ADJ

K1 VIN

K2 VIN

K3 FIN

K5 GND

K6 GND

K7 PGOOD

L1 VIN

L2 VIN

L3 FIN

L5 RUN/SS

L6 SYNC

L7 GND

Table 3. LTM8031 Pinout (Sorted by Pin Number)

LTM8031

8031fb

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.

revision hisTory

REV DATE DESCRIPTION PAGE NUMBER

A 03/10 Addition to Features

Changes to Applications Information

B 04/12 Added MP-Grade part. Reﬂected throughout the data sheet 1-22

LTM8031

8031fb

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

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

 LINEAR TECHNOLOGY CORPORATION 2009

LT 0412 REV B • PRINTED IN USA

relaTeD parTs

PART NUMBER DESCRIPTION COMMENTS

LTM4606 Ultralow Noise 6A DC/DC µModule Regulator 4.5V ≤ VIN ≤ 28V, 0.6V ≤ VOUT ≤ 5V, 15mm × 15mm × 2.8mm LGA

LTM4612 Ultralow Noise High VOUT DC/DC µModule Regulator 5A, 5V ≤ VIN ≤ 36V, 3.3V ≤ VOUT ≤ 15V, 15mm × 15mm × 2.8mm LGA

LTM8023 36V, 2A DC/DC µModule Regulator 3.6V ≤ VIN ≤ 36V, 0.8V ≤ VOUT ≤ 10V, 9mm × 11.75mm × 2.8mm LGA

LTM8025 36V, 3A DC/DC µModule Regulator 3.6V ≤ VIN ≤ 36V, 0.8V ≤ VOUT ≤ 24V, 9mm × 15mm × 4.32mm LGA

LTM8032 36V, 2A EMC DC/DC µModule Regulator EN55022 Class B, 9mm × 15mm × 2.8mm LGA. Pin Compatible with the

LTM8031

8V Step-Down Converter

VIN

FIN

1µF

4.7µF

26.7k23.7k

VOUT

RUN/SS

VIN*

10.5V TO 36V

PGOOD

BIAS

LTM8031

AUX

OUT

SYNC GND

8031 TA06

ADJ

*RUNNING VOLTAGE RANGE.

SEE APPLICATIONS FOR START-UP DETAILS

Typical applicaTion