Datasheet LT1615-1, LT1615 Datasheet (Linear Technology)

FEATURES

LT1615/LT1615-1

Micropower Step-Up

DC/DC Converters

in SOT-23

U

DESCRIPTIO

■

Low Quiescent Current:

20µA in Active Mode
<1µA in Shutdown Mode

■

Operates with VIN as Low as 1V

■

Low V

■

Tiny 5-Lead SOT-23 Package

■

Uses Small Surface Mount Components

■

High Output Voltage: Up to 34V

Switch: 250mV at 300mA

CESAT

U

APPLICATIO S

■

LCD Bias

■

Handheld Computers

■

Battery Backup

■

Digital Cameras

The LT®1615/LT1615-1 are micropower step-up DC/DC
converters in a 5-lead SOT-23 package. The LT1615 is
designed for higher power systems with a 350mA current
limit and an input voltage range of 1.2V to 15V, whereas
the LT1615-1 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, result­ing in high efficiency over a broad range of load current.
The 36V switch allows high voltage outputs up to 34V to
be easily generated in a simple boost topology without the
use of costly transformers. The LT1615’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.

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

TYPICAL APPLICATIO

1-Cell Li-Ion to 20V Converter for LCD Bias

L1

V

IN

SHDN

10µH

LT1615

GND

V

2.5V TO 4.2V

IN

C1

4.7µF

C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN TMK316BJ105
D1: MOTOROLA MBR0530
L1: MURATA LQH3C100K24

SW

U

Efficiency

85

D1

R1
2M

FB

R2
130k

20V
12mA

C2
1µF

1615/-1 TA01

80

VIN = 4.2V

75

70

65

EFFICIENCY (%)

60

55

50

0.1 0.3

VIN = 2.5V

1 3 10 30

LOAD CURRENT (mA)

VIN = 3.3V

1615/-1 TA01a

1

LT1615/LT1615-1

WW

W

ABSOLUTE AXI U RATI GS

(Note 1)

U

UUW

PACKAGE/ORDER I FOR A TIO

ORDER PART

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

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

FB Voltage .................................................................V

IN

GND 2

Current into FB 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

Consult factory for Industrial and Military grade parts.

ELECTRICAL CHARACTERISTICS

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

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Input Voltage LT1615-1 1.0 V

LT1615 1.2 V

Quiescent Current Not Switching 20 30 µA

= 0V 1 µA

V

SHDN

FB Comparator Trip Point ● 1.205 1.23 1.255 V
FB Comparator Hysteresis 8mV
Output Voltage Line Regulation 1.2V < VIN < 12V 0.05 0.1 %/V
FB Pin Bias Current (Note 3) VFB = 1.23V ● 30 80 nA
Switch Off Time VFB > 1V 400 ns

< 0.6V 1.5 µs

V

FB

Switch V

CESAT

Switch Current Limit LT1615-1 75 100 125 mA

SHDN Pin Current V

SHDN Input Voltage High 0.9 V
SHDN Input Voltage Low 0.25 V
Switch Leakage Current Switch Off, VSW = 5V 0.01 5 µA

I

= 70mA (LT1615-1) 85 120 mV

SW

I

= 300mA (LT1615) 250 350 mV

SW

LT1615 300 350 400 mA

= 1.2V 2 3 µA

SHDN

= 5V 8 12 µA

V

SHDN

The ● denotes the specifications which apply over the full operating

SHDN

TOP VIEW

SW 1

FB 3

S5 PACKAGE

5-LEAD PLASTIC SOT-23

T

= 125°C, θJA = 256°C/W

JMAX

= 1.2V unless otherwise noted.

5 V

IN

4 SHDN

NUMBER

LT1615ES5
LT1615ES5-1

S5 PART MARKING

LTIZ
LTKH

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: The LT1615 and LT1615-1 are guaranteed to meet performance
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 into the FB pin.

2

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LT1615/LT1615-1

Switch Saturation Voltage
(V

) Quiescent Current

CESAT

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

SWITCH VOLTAGE (V)

0.20

0.15

0.10
–25 0 25 50 75 100

–50

TEMPERATURE (°C)

I

SWITCH

I

SWITCH

= 500mA

= 300mA

1615/-1 G01

Feedback Pin Voltage and
Bias Current

1.25

1.24

1.23

1.22

FEEDBACK VOLTAGE (V)

1.21

1.20
–50

–25 0 25 50 75 100

Switch Off Time Shutdown Pin CurrentSwitch Current Limit

550

500

450

400

350

SWITCH OFF TIME (ns)

300

250

–50 –25 0 25 50 75 100

VIN = 1.2V

VIN = 12V

TEMPERATURE (°C)

1615/-1 G04

400

VIN = 12V

350

LT1615

300
250
200
150

LT1615-1

PEAK CURRENT (mA)

100

50

0

–50 –25 0 25 50 75 100

VOLTAGE

CURRENT

TEMPERATURE (°C)

VIN = 1.2V

VIN = 12V

VIN = 1.2V

TEMPERATURE (°C)

1615/-1 G02

1615/-1 G05

50

40

BIAS CURRENT (nA)

30

20

10

0

QUIESCENT CURRENT (µA)

SHUTDOWN PIN CURRENT (µA)

25

VFB = 1.23V
NOT SWITCHING

23

21

19

17

15

–50 –25 0 25 50 75 100

25

20

15

10

5

0

0 5 10 15

VIN = 12V

VIN = 1.2V

TEMPERATURE (°C)

1615/-1 G03

25°C

100°C

SHUTDOWN PIN VOLTAGE (V)

1615/-1 G03

UUU

PI FU CTIO S

SW (Pin 1): Switch Pin. This is the collector of the internal
NPN power switch. Minimize the metal trace area con­nected to this pin to minimize EMI.

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

FB (Pin 3): Feedback Pin. Set the output voltage by
selecting values for R1 and R2 (see Figure 1):

RR

12



V



123



OUT

.



1=−





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.

VIN (Pin 5): Input Supply Pin. Bypass this pin with a
capacitor as close to the device as possible.

3

LT1615/LT1615-1

BLOCK DIAGRA

W

(EXTERNAL)

(EXTERNAL)

V

IN

C1

V

OUT

V

IN

5

R5
40k

R6
40k

SHDN

4

A1

+

L1

ENABLE

D1

V

OUT

SW

1

C2

–

R1

FB

3

R2

Q1

Q2
X10

R3
30k

400ns

ONE-SHOT

RESET

Q3

DRIVER

+

* 12mV FOR LT1615-1

R4
140k

A2

–

42mV*

0.12Ω

GND

2

1615/-1 BD

Figure 1. LT1615 Block Diagram

U

OPERATIO

The LT1615 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 FB pin is slightly above

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 FB pin
drops below the lower hysteresis point of A1 (typical
hysteresis at the FB pin is 8mV). A1 then enables the
internal circuitry, turns on power switch Q3, and the
current in inductor L1 begins ramping up. Once the switch
current reaches 350mA, comparator A2 resets the one­shot, which turns off Q3 for 400ns. L1 then delivers
current to the output through diode D1 as the inductor
current ramps down. Q3 turns on again and the inductor

current ramps back up to 350mA, then A2 resets the one­shot, again allowing L1 to deliver current to the output.
This switching action continues until the output voltage is
charged up (until the FB pin reaches 1.23V), then A1 turns
off the internal circuitry and the cycle repeats. The LT1615
contains additional circuitry to provide protection during
start-up and under short-circuit conditions. When the FB
pin voltage is less than approximately 600mV, the switch
off-time is increased to 1.5µs and the current limit is
reduced to around 250mA (70% of its normal value). This
reduces the average inductor current and helps minimize
the power dissipation in the LT1615 power switch and in
the external inductor and diode. The LT1615-1 operates in
the same manner, except the switch current is limited to
100mA (the A2 reference voltage is 12mV instead of
42mV).

4

LT1615/LT1615-1

U

WUU

APPLICATIO S I FOR A TIO

Choosing an Inductor

Several recommended inductors that work well with the
LT1615 and LT1615-1 are listed in Table 1, although there
are many other manufacturers and devices that can be
used. Consult each manufacturer for more detailed infor­mation 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 (µH) MAX DCR (Ω) VENDOR

LQH3C4R7 4.7 0.26 Murata
LQH3C100 10 0.30 [phone]
LQH3C220 22 0.92 www.murata.com

CD43-4R7 4.7 0.11 Sumida
CD43-100 10 0.18 [phone]
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 [phone]
DO1608-223 22 0.37 www.coilcraft.com

output voltages below 7V, a 4.7µH inductor is the best
choice, even though the equation above might specify a
smaller value. This is due to the inductor current over­shoot that occurs when very small inductor values are
used (see Current Limit Overshoot section).

For higher output voltages, the formula above will give
large inductance values. For a 2V to 20V converter (typical
LCD Bias application), a 21µH inductor is called for with
the above equation, but a 10µH inductor could be used
without excessive reduction in maximum output current.

Inductor Selection—SEPIC Regulator

The formula below calculates the approximate inductor
value to be used for a SEPIC regulator using the LT1615.
As for the boost inductor selection, a larger or smaller
value can be used.



VV

=

2





OUT D

I

LIM

L



+

t

OFF





Inductor Selection—Boost Regulator

The formula below calculates the appropriate inductor
value to be used for a boost regulator using the LT1615 or
LT1615-1 (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.
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 in­crease 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:

VV V

−+

OUT

L

=

IN MIN

()

I

LIM

where VD = 0.4V (Schottky diode voltage), I
100mA, and t

= 400ns; for designs with varying V

OFF

D

t

OFF

= 350mA or

LIM

IN

such as battery powered applications, use the minimum
VIN value in the above equation. For most systems with

Current Limit Overshoot

For the constant off-time control scheme of the LT1615,
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:

II

=+

PEAK LIM

Where V

SAT



VV

IN MAX SAT




−

()

L

= 0.25V (switch saturation voltage). The






100

ns

current overshoot will be most evident for systems with
high input voltages and for systems where smaller induc­tor 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 over­shoot can be quite high. Although it is internally current

5

LT1615/LT1615-1

U

WUU

APPLICATIO S I FOR A TIO

limited to 350mA, the power switch of the LT1615 can
handle larger currents without problem, but the overall
efficiency will suffer. Best results will be obtained when
I

is kept below 700mA for the LT1615 and below

PEAK

400mA for the LT1615-1.

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 LT1615’s SOT-23 package. Solid tantalum capaci­tors (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 higher 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 LT1615. 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 LT1615 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
LT1615. 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 0.35A. For LT1615-1 applica­tions, a Philips BAT54 or 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 LT1615 pro­vides 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 4.7pF feed-forward capaci­tor in the feedback network of the LT1615 (see the circuits
in the Typical Applications section). Adding this small,
inexpensive 4.7pF capacitor will greatly reduce the output
voltage ripple.

6

Table 2. Recommended Capacitors

CAPACITOR TYPE VENDOR

Ceramic Taiyo Yuden

[phone]
www.t-yuden.com

Ceramic AVX

[phone]
www.avxcorp.com

Ceramic Murata

[phone]
www.murata.com

U

V

IN

SW

FB

LT1615

V

IN

3V TO 6V

L1

10µH

D1

C3

1µF

SHDN

324k

1M

C2
10µF

5V
100mA

1615/-1 TA07

GND

C1

4.7µF

C1: TAIYO YUDEN LMK316BJ475 [phone]
C2: TAIYO YUDEN JMK316BJ106 [phone]
C3: TAIYO YUDEN JMK107BJ105 [phone]
L1, L2: MURATA LQH3C100K24 [phone]
D1: MOTOROLA MBR0520 [phone]

L2
10µH

43

2

15

4.7pF

TYPICAL APPLICATIO S

LT1615/LT1615-1

1.5V TO 3V

V

2.5V TO 4.2V

2-Cell to 3.3V Boost Converter

L1

V

IN

C1

4.7µF

C1: TAIYO YUDEN LMK316BJ475 [phone]
C2: TAIYO YUDEN JMK325BJ226 [phone]
L1: MURATA LQH3C4R7M24 [phone]
D1: MOTOROLA MBR0520 [phone]

4.7µH

V

IN

LT1615

43

SHDN

GND

D1

15

SW

FB

2

1-Cell Li-Ion to 3.3V SEPIC Converter

C3

L1

IN

C1

4.7µF

C1: TAIYO YUDEN LMK316BJ475 [phone]
C2: TAIYO YUDEN JMK316BJ106 [phone]
C3: TAIYO YUDEN JMK107BJ105 [phone]
L1, L2: MURATA LQH3C100K24 [phone]
D1: MOTOROLA MBR0520 [phone]

10µH

V

IN

LT1615

43

SHDN

1µF

15

SW

FB

GND

2

L2
10µH

2-Cell to 3.3V Converter Efficiency

90
85
80
75
70
65

EFFICIENCY (%)

60
55
50

0.1

VIN = 3V

VIN = 1.5V

1 10 100

LOAD CURRENT (mA)

1615/-1 TA03a

1M

604k

4.7pF

3.3V
60mA

C2
22µF

1615/-1 TA03

4-Cell to 5V SEPIC Converter

D1

1M

604k

4.7pF

3.3V
100mA

C2
10µF

1615/-1 TA07

V

IN

1V TO 6V

C1

4.7µF

C1: TAIYO YUDEN EMK316BJ475 [phone]
C2: TAIYO YUDEN GMK316BJ105 [phone]
L1: MURATA LQH3C220K24 [phone]
D1: MOTOROLA MBR0540 [phone]

PIN Diode Driver

L1

22µH

V

IN

LT1615-1

43

SHDN

GND

D1

15

SW

FB

2

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 represen-

10M

365k

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

35V
500µA

C2
1µF

1615/-1 TA09

1-Cell to 3.3V Boost Converter

L1

V

IN

1V TO 1.5V

C1

4.7µF

C1: TAIYO YUDEN LMK316BJ475 [phone]
C2: TAIYO YUDEN JMK316BJ106 [phone]
L1: MURATA LQH3C220K24 [phone]
D1: CENTRAL SEMICONDUCTOR CMDSH-3 [phone]

22µH

15

V

IN

43

SHDN

SW

LT1615-1

FB

GND

2

D1

4.7pF

1M

604k

3.3V
15mA

C2
10µF

1615/-1 TA04

7

LT1615/LT1615-1

U

TYPICAL APPLICATIO S

V

IN

1.5V TO 5V

C1: TAIYO YUDEN LMK316BJ475 [phone]
C2, C3, C4: TAIYO YUDEN TMK316BJ105 [phone]
C5: TAIYO YUDEN LMK212BJ105 [phone]
L1: MURATA LQH3C100K24 [phone]
D1, D2, D3, D4: MOTOROLA MBR0530 [phone]

PACKAGE DESCRIPTIO

±20V Dual Output Converter with Load Disconnect

D3

C4

1µF

L1

10µH

V

IN

43

SHDN

C1

4.7µF

SW

LT1615

GND

2

C5

1µF

15

FB

D2

D1

4.7pF

D4

2M

130k

U

Dimensions in millimeters (inches) unless otherwise noted.

–20V
4mA

C3
1µF

20V
4mA

C2
1µF

1615/-1 TA05

S5 Package

5-Lead Plastic SOT-23

(LTC DWG # 05-08-1633)

2.60 – 3.00

(0.102 – 0.118)

1.50 – 1.75

(0.059 – 0.069)

0.35 – 0.55

(0.014 – 0.022)

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)

0.09 – 0.20

(0.004 – 0.008)

(NOTE 2)

0.00 – 0.15

(0.00 – 0.006)

0.35 – 0.50

(0.014 – 0.020)

FIVE PLACES (NOTE 2)

0.90 – 1.45

(0.035 – 0.057)

0.90 – 1.30

(0.035 – 0.051)

2.80 – 3.00

(0.110 – 0.118)

(NOTE 3)

(0.074)

1.90

REF

0.95

(0.037)

REF

S5 SOT-23 0599

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

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LT1611 1.4MHz Inverting Switching Regulator in 5-Lead SOT-23 –5V at 150mA from 5V Input, Tiny SOT-23 Package
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LT1617 Micropower Inverting DC/DC Converter in 5-Lead SOT-23 –15V at 12mA from 2.5V Input, Tiny SOT-23 Package
Burst Mode is a trademark of Linear Technology Corporation

8

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com

16151f LT/TP 1099 4K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1998