LT1617ES5#TRMPBF - Linear Technology

LT1617/LT1617-1

TYPICAL APPLICATION

APPLICATIO S

DESCRIPTIO

FEATURES

Micropower Inverting

DC/DC Converters

in SOT-23

The LT

1617/LT1617-1 are micropower inverting DC/DC

converters in a 5-lead SOT-23 package. The LT1617 is

designed for higher power systems with a 350mA current

limit and an input voltage range of 1.2V to 15V, whereas

the LT1617-1 is intended for lower power and single-cell

applications with a 100mA current limit and an extended

input voltage range of 1V to 15V. Otherwise, the two

devices are functionally equivalent. Both devices feature a

quiescent current of only 20µA at no load, which further

reduces to 0.5µA in shutdown. A current limited, fixed off-

time control scheme conserves operating current, result-

ing in high efficiency over a broad range of load current.

The 36V switch allows high voltage outputs up to –34V to

be easily generated without the use of costly transformers.

The LT1617’s low off-time of 400ns permits the use of

tiny, low profile inductors and capacitors to minimize

footprint and cost in space-conscious portable applications.

■

Low Quiescent Current:

A in Active Mode

A in Shutdown Mode

■

Operates with V

as Low as 1V

■

Low V

CESAT

Switch: 250mV at 300mA

■

Uses Small Surface Mount Components

■

High Output Voltage: Up to –34V

■

Tiny 5-Lead SOT-23 Package

■

LCD Bias

■

Handheld Computers

■

Battery Backup

■

Digital Cameras

, LTC and LT are registered trademarks of Linear Technology Corporation.

1-Cell Li-Ion to –15V Inverting Converter Efficiency

NFB

LT1617

2.5V TO 4.2V

22µH

SHDN

24.9k

267k C2

4.7µF

–15V

12mA

1617/-1 TA01

GND

4.7µF

C1: TAIYO YUDEN LMK316BJ475

C2: TAIYO YUDEN EMK316BJ475

C3: TAIYO YUDEN TMK316BJ224

L1, L2: MURATA LQH3C220K34

D1: MOTOROLA MBR0530

22µH

0.22µF

LOAD CURRENT (mA)

0.1 1 10 30

EFFICIENCY (%)

1617/-1 TA01a

= 4.2V

= 2.5V

LT1617/LT1617-1

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

UUW

(Note 1)

, SHDN Voltage................................................... 15V

SW Voltage .............................................................. 36V

NFB Voltage ............................................................. –3V

Current into NFB Pin ............................................. –1mA

Junction Temperature...........................................125°C

Operating Temperature Range (Note 2) .. –40°C to 85°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)..................300°C

ORDER PART

NUMBER

LT1617ES5

LT1617ES5-1

Consult factory for Industrial and Military grade parts.

S5 PART MARKING

SW 1

GND 2

TOP VIEW

S5 PACKAGE

5-LEAD PLASTIC SOT-23

NFB 3

5 V

4 SHDN

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Input Voltage LT1617-1 1.0 V

LT1617 1.2 V

Quiescent Current Not Switching 20 30 µA

SHDN

= 0V 1µA

FB Comparator Trip Point ●–1.205 –1.23 –1.255 V

FB Comparator Hysteresis 8mV

Output Voltage Line Regulation 1.2V < V

< 12V 0.05 0.1 %/V

FB Pin Bias Current (Note 3) V

NFB

= –1.23V ●1.3 2 2.7 µA

Switch Off Time 400 ns

Switch V

CESAT

= 60mA (LT1617-1) 85 120 mV

= 300mA (LT1617) 250 350 mV

Switch Current Limit LT1617-1 75 100 125 mA

LT1617 300 350 400 mA

SHDN Pin Current V

SHDN

= 1.2V 2 3 µA

SHDN

= 5V 8 12 µA

SHDN Input Voltage High 0.9 V

SHDN Input Voltage Low 0.25 V

Switch Leakage Current Switch Off, V

= 5V 0.01 5 µA

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

Note 2: The LT1617 and LT1617-1 are guaranteed to meet specifications

from 0°C to 70°C. Specifications over the –40°C to 85°C operating

temperature range are assured by design, characterization and correlation

with statistical process controls.

Note 3: Bias current flows out of the NFB pin.

JMAX

= 125°C, θ

= 256°C/W

temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VSHDN = 1.2V unless otherwise noted.

LTKF

LTKA

LT1617/LT1617-1

TYPICAL PERFOR A CE CHARACTERISTICS

Switch Saturation Voltage

(VCESAT)Quiescent Current

Feedback Pin Voltage and

Bias Current

TEMPERATURE (°C)

–50 –25 0 25 50 75 100

SWITCH VOLTAGE (V)

1617/-1 G01

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

SWITCH

= 500mA

SWITCH

= 300mA

TEMPERATURE (°C)

–50

FEEDBACK VOLTAGE (V)

1617/-1 G02

–1.25

–1.24

–1.23

–1.22

–1.21

–1.20

BIAS CURRENT (µA)

CURRENT

VOLTAGE

–25 0 25 50 75 100

TEMPERATURE (°C)

QUIESCENT CURRENT (µA)

1617/-1 G03

–50 –25 0 25 50 75 100

= 12V

= 1.2V

= 1.23V

NOT SWITCHING

PI FU CTIO S

UUU

SW (Pin 1): Switch Pin. This is the collector of the internal

NPN power switch. Minimize the metal trace area con-

nected to this pin to minimize EMI.

GND (Pin 2): Ground. Tie this pin directly to the local

ground plane.

NFB (Pin 3): Feedback Pin. Set the output voltage by

selecting values for R1 and R2 (see Figure 1):

OUT

1123

123

2210

=−

()

−

.•

SHDN (Pin 4): Shutdown Pin. Tie this pin to 0.9V or higher

to enable the device. Tie below 0.25V to turn off the device.

(Pin 5): Input Supply Pin. Bypass this pin with a

capacitor as close to the device as possible.

TEMPERATURE (°C)

SWITCH OFF TIME (ns)

1617/-1 G04

550

500

450

400

350

300

250

–50 –25 0 25 50 75 100

= 1.2V

= 12V

TEMPERATURE (°C)

SWITCH CURRENT LIMIT (mA)

1617/-1 G05

400

350

300

250

200

150

100

–50 –25 0 25 50 75 100

= 1.2V

= 12V

= 1.2V

LT1617-1

LT1617

= 12V

SHUTDOWN PIN VOLTAGE (V)

SHUTDOWN PIN CURRENT (µA)

1617/-1 G06

00 5 10 15

25°C

100°C

Switch Off Time Shutdown Pin CurrentSwitch Current Limit

LT1617/LT1617-1

BLOCK DIAGRA

Figure 1. LT1617 Block Diagram

–

400ns

ONE-SHOT DRIVER

RESET

ENABLE

42mV*

0.12Ω

280k

60k

80k

X10

VIN

NFB

4SHDN 1SW

GND

1617/-1 BD

VOUT

VIN

(EXTERNAL)

VOUT

* 12mV FOR LT1617-1

OPERATIO

The LT1617 uses a constant off-time control scheme to

provide high efficiencies over a wide range of output

current. Operation can be best understood by referring to

the block diagram in Figure 1. Q1 and Q2 along with R3 and

R4 form a bandgap reference used to regulate the output

voltage. When the voltage at the NFB pin is slightly below

–1.23V, comparator A1 disables most of the internal

circuitry. Output current is then provided by capacitor C2,

which slowly discharges until the voltage at the NFB pin

goes above the hysteresis point of A1 (typical hysteresis

at the NFB pin is 8mV). A1 then enables the internal

circuitry, turns on power switch Q3, and the current in

inductors L1 and L2 begins ramping up. Once the switch

current reaches 350mA, comparator A2 resets the one-

shot, which turns off Q3 for 400ns. L2 continues to deliver

current to the output while Q3 is off. Q3 turns on again and

the inductor currents ramp back up until the switch

current reaches 350mA, then A2 again resets the one-

shot. This switching action continues until the output

voltage is charged up (until the NFB pin reaches –1.23V),

then A1 turns off the internal circuitry and the cycle

repeats. The LT1617-1 operates in the same manner,

except the switch current is limited to 100mA (the A2

reference voltage is 12mV instead of 42mV).

LT1617/LT1617-1

Choosing an Inductor

Several recommended inductors that work well with the

LT1617 and LT1617-1 are listed in Table 1, although there

are many other manufacturers and devices that can be

used. Consult each manufacturer for more detailed infor-

mation and for their entire selection of related parts. Many

different sizes and shapes are available. Use the equations

and recommendations in the next few sections to find the

correct inductance value for your design.

Table 1. Recommended Inductors

PART VALUE (

H) MAX DCR (

Ω

) VENDOR

LQH3C4R7 4.7 0.26 Murata

LQH3C100 10 0.30 (714) 852-2001

LQH3C220 22 0.92 www.murata.com

CD43-4R7 4.7 0.11 Sumida

CD43-100 10 0.18 (847) 956-0666

CDRH4D18-4R7 4.7 0.16 www.sumida.com

CDRH4D18-100 10 0.20

DO1608-472 4.7 0.09 Coilcraft

DO1608-103 10 0.16 (847) 639-6400

D01608-223 22 www.coilcraft.com

Inductor Selection—Inverting Regulator

The formula below calculates the appropriate inductor

value to be used for an inverting regulator using the

LT1617 or LT1617-1 (or at least provides a good starting

point). This value provides a good tradeoff in inductor size

and system performance. Pick a standard inductor close

to this value (both inductors should be the same value). A

larger value can be used to slightly increase the available

output current, but limit it to around twice the value

calculated below, as too large of an inductance will in-

crease the output voltage ripple without providing much

additional output current. A smaller value can be used

(especially for systems with output voltages greater than

12V) to give a smaller physical size. Inductance can be

calculated as:

LVV

OUT D

LIM OFF













where V

= 0.4V (Schottky diode voltage), I

LIM

= 350mA or

100mA, and t

OFF

= 400ns.

APPLICATIO S I FOR ATIO

WUUU

For higher output voltages, the formula above will give

large inductance values. For a 2V to 20V converter (typical

LCD bias application), a 47µH inductor is called for with

the above equation, but a 10µH or 22µH inductor could be

used without excessive reduction in maximum output

current.

Inductor Selection—Inverting Charge Pump Regulator

For the inverting regulator, the voltage seen by the internal

power switch is equal to the sum of the absolute value of

the input and output voltages, so that generating high

output voltages from a high input voltage source will often

exceed the 36V maximum switch rating. For instance, a

12V to –30V converter using the inverting topology would

generate 42V on the SW pin, exceeding its maximum

rating. For such a system, an inverting charge pump is the

best topology.

The formula below calculates the approximate inductor

value to be used for an inverting charge pump regulator

using the LT1617. As for the boost inductor selection, a

larger or smaller value can be used. For designs with

varying V

such as battery powered applications, use the

minimum V

value in the equation below.

LVV V

OUT IN MIN D

LIM OFF

=−+

()

Current Limit Overshoot

For the constant off-time control scheme of the LT1617,

the power switch is turned off only after the 350mA (or

100mA) current limit is reached. There is a 100ns delay

between the time when the current limit is reached and

when the switch actually turns off. During this delay, the

inductor current exceeds the current limit by a small

amount. The peak inductor current can be calculated by:

IIVV

Lns

PEAK LIM IN MAX SAT

=+ −











()

100

Where V

SAT

= 0.25V (switch saturation voltage). The

current overshoot will be most evident for systems with

high input voltages and for systems where smaller induc-

LT1617/LT1617-1

APPLICATIO S I FOR ATIO

WUUU

tor values are used. This overshoot can be beneficial as it

helps increase the amount of available output current for

smaller inductor values. This will be the peak current seen

by the inductor (and the diode) during normal operation.

For designs using small inductance values (especially at

input voltages greater than 5V), the current limit over-

shoot can be quite high. Although it is internally current

limited to 350mA, the power switch of the LT1617 can

handle larger currents without problem, but the overall

efficiency will suffer. Best results will be obtained when

PEAK

is kept below 700mA for the LT1617 and below

400mA for the LT1617-1.

Capacitor Selection

Low ESR (Equivalent Series Resistance) capacitors should

be used at the output to minimize the output ripple voltage.

Multilayer ceramic capacitors are the best choice, as they

have a very low ESR and are available in very small

packages. Their small size makes them a good companion

to the LT1617’s SOT-23 package. Solid tantalum capaci-

tors (like the AVX TPS, Sprague 593D families) or OS-CON

capacitors can be used, but they will occupy more board

area than a ceramic and will have a larger ESR. Always use

a capacitor with a sufficient voltage rating.

Ceramic capacitors also make a good choice for the input

decoupling capacitor, which should be placed as close as

possible to the LT1617. A 4.7µF input capacitor is suffi-

cient for most applications. Table 2 shows a list of several

capacitor manufacturers. Consult the manufacturers for

more detailed information and for their entire selection of

related parts.

Diode Selection

For most LT1617 applications, the Motorola MBR0520

surface mount Schottky diode (0.5A, 20V) is an ideal

choice. Schottky diodes, with their low forward voltage

drop and fast switching speed, are the best match for the

LT1617. For higher output voltage applications the 30V

MBR0530 can be used. Many different manufacturers

make equivalent parts, but make sure that the component

is rated to handle at least 0.5A. For LT1617-1 applications,

a Phillips BAT54 or a Central Semiconductor CMDSH-3

works well.

Lowering Output Voltage Ripple

Using low ESR capacitors will help minimize the output

ripple voltage, but proper selection of the inductor and the

output capacitor also plays a big role. The LT1617 pro-

vides energy to the load in bursts by ramping up the

inductor current, then delivering that current to the load.

If too large of an inductor value or too small of a capacitor

value is used, the output ripple voltage will increase

because the capacitor will be slightly overcharged each

burst cycle. To reduce the output ripple, increase the

output capacitor value or add a 100pF feed-forward ca-

pacitor in the feedback network of the LT1617 (see the

circuits in the Typical Applications section). Adding this

small, inexpensive 100pF capacitor will greatly reduce the

output voltage ripple.

Table 2. Recommended Capacitors

CAPACITOR TYPE VENDOR

Ceramic Taiyo Yuden

(408) 573-4150

www.t-yuden.com

Ceramic AVX

(803) 448-9411

www.avxcorp.com

Ceramic Murata

(714) 852-2001

www.murata.com

LT1617/LT1617-1

TYPICAL APPLICATIO S

–33V Inverting Charge Pump Converter

NFB

LT1617

10µHD2

SHDN

24.9k

619k C2

1µF

–33V

20mA

1617/-1 TA03

GND

4.7µF

C1: TAIYO YUDEN LMK316BJ475 (408) 573-4150

C2: TAIYO YUDEN GMK316BJ105 (408) 573-4150

C3: TAIYO YUDEN GMK212BJ224 (408) 573-4150

L1: MURATA LQH3C100K24 (814) 237-1431

D1: MOTOROLA MBR0540 (800) 441-2447

0.22µF

NFB

LT1617

10µH

SHDN

24.9k

73.2k C2

10µF

–5V

100mA

1617/-1 TA02

GND

4.7µF

C1: TAIYO YUDEN LMK316BJ475 (408) 573-4150

C2: TAIYO YUDEN JMK316BJ106 (408) 573-4150

C3: TAIYO YUDEN EMK212BJ474 (408) 573-4150

L1, L2: MURATA LQH3C100K24 (814) 237-1431

D1: MOTOROLA MBR0520 (800) 441-2447

10µH

0.47µF

100pF

5V to –5V Inverting Converter

1-Cell to –9V Inverting Converter

NFB

LT1617-1

47µH

SHDN

24.9k

150k C2

4.7µF

–9V

2.5mA

1V TO 1.5V

1617/-1 TA02

GND

4.7µF

C1: TAIYO YUDEN LMK316BJ475 (408) 573-4150

C2: TAIYO YUDEN EMK316BJ475 (408) 573-4150

C3: TAIYO YUDEN TMK316BJ224 (408) 573-4150

L1, L2: MURATA LQH3C470K34 (814) 237-1431

D1: CENTRAL SEMICONDUCTOR CMDSH-3 (516) 435-1110

47µH

0.22µF

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 representation that the

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

LT1617/LT1617-1

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900

●

FAX: (408) 434-0507

●

www.linear-tech.com

 LINEAR TECHNOLOGY CORPORATION 1999

16171f LT/TP 0200 4K • PRINTED IN USA

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Burst Mode is a trademark of Linear Technology Corporation

PACKAGE DESCRIPTIO

Dimensions in millimeters (inches) unless otherwise noted.

S5 Package

5-Lead Plastic SOT-23

(LTC DWG # 05-08-1633)

0.95

(0.037)

REF

1.50 – 1.75

(0.059 – 0.069)

0.10 – 0.60

(0.004 – 0.024)

REF

0.35 – 0.50

(0.014 – 0.020)

FIVE PLACES (NOTE 2)

S5 SOT-23 0797

2.80 – 3.00

(0.110 – 0.118)

(NOTE 3)

1.90

(0.074)

REF

0.90 – 1.45

(0.035 – 0.057)

0.90 – 1.30

(0.035 – 0.051)

0.00 – 0.15

(0.00 – 0.006)

0.09 – 0.20

(0.004 – 0.008)

(NOTE 2)

2.60 – 3.00

(0.102 – 0.118)

NOTE:

1. DIMENSIONS ARE IN MILLIMETERS

2. DIMENSIONS ARE INCLUSIVE OF PLATING

3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR

4. MOLD FLASH SHALL NOT EXCEED 0.254mm

5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)

TYPICAL APPLICATIO S

±20V Dual Output Converter with Load Disconnect

NFB

LT1617

1.5V TO 5V

10µHD1

SHDN

24.9k

267k C2

1µF

–20V

4mA

20V

4mA

1617/-1 TA04

GND

1µF

4.7µF

C1: TAIYO YUDEN LMK316BJ475 (408) 573-4150

C2, C3, C4: TAIYO YUDEN TMK316BJ105 (408) 573-4150

C5: TAIYO YUDEN LMK212BJ105 (408) 573-4150

L1: MURATA LQH3C100K24 (814) 237-1431

D1, D2, D3, D4: MOTOROLA MBR0530 (800) 441-2447

15 100pF

1µFC4

1µF