Datasheet LT1617-1 Datasheet (Linear Technology)

FEATURES

LT1617/LT1617-1

Micropower Inverting

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

■

Uses Small Surface Mount Components

■

High Output Voltage: Up to –34V

■

Tiny 5-Lead SOT-23 Package

Switch: 250mV at 300mA

CESAT

U

APPLICATIO S

■

LCD Bias

■

Handheld Computers

■

Battery Backup

■

Digital Cameras

U

TYPICAL APPLICATION

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, 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 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.

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

V

2.5V TO 4.2V

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

C3

0.22µF

15

SW

NFB

2

IN

V

43

SHDN

C1

4.7µF

C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN EMK316BJ475
C3: TAIYO YUDEN TMK316BJ224
L1, L2: MURATA LQH3C220K34
D1: MOTOROLA MBR0530

IN

L1

22µH

LT1617

GND

D1

L2

22µH

267k

24.9k

–15V
12mA

C2

4.7µF

1617/-1 TA01

Efficiency

80

75

70

65

EFFICIENCY (%)

60

55

50

0.1 1 10 30

VIN = 4.2V

VIN = 2.5V

LOAD CURRENT (mA)

1617/-1 TA01a

1

LT1617/LT1617-1

WW

W

ABSOLUTE AXI U RATI GS

(Note 1)

U

UUW

PACKAGE/ORDER I FOR ATIO

ORDER PART

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

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

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

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

GND 2

NFB 3

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 LT1617-1 1.0 V

LT1617 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) V
Switch Off Time 400 ns
Switch V

CESAT

Switch Current Limit LT1617-1 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

= –1.23V ● 1.3 2 2.7 µA

NFB

I

= 60mA (LT1617-1) 85 120 mV

SW

= 300mA (LT1617) 250 350 mV

I

SW

LT1617 300 350 400 mA

= 1.2V 2 3 µA

SHDN

V

= 5V 8 12 µA

SHDN

The ● denotes the specifications which apply over the full operating

SHDN

TOP VIEW

SW 1

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

LT1617ES5
LT1617ES5-1

S5 PART MARKING

LTKF
LTKA

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.

2

UW

R

V

R

OUT

1

123

123

2

210

6

=

−

+

()

−

.

.

•

TYPICAL PERFOR A CE CHARACTERISTICS

LT1617/LT1617-1

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

1617/-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)

1617/-1 G04

400

VIN = 12V

350

LT1617

300

250

200

150

LT1617-1

100

SWITCH CURRENT LIMIT (mA)

50

0

–50 –25 0 25 50 75 100

VOLTAGE

CURRENT

TEMPERATURE (°C)

VIN = 1.2V

VIN = 12V

VIN = 1.2V

TEMPERATURE (°C)

1617/-1 G02

1617/-1 G05

5

4

BIAS CURRENT (µA)

3

2

1

0

25

VFB = 1.23V
NOT SWITCHING

23

21

19

QUIESCENT CURRENT (µA)

17

15

–50 –25 0 25 50 75 100

25

20

15

10

5

SHUTDOWN PIN CURRENT (µA)

0

0 5 10 15

VIN = 12V

VIN = 1.2V

TEMPERATURE (°C)

25°C

100°C

SHUTDOWN PIN VOLTAGE (V)

1617/-1 G03

1617/-1 G06

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.

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

LT1617/LT1617-1

BLOCK DIAGRA

W

(EXTERNAL)

(EXTERNAL)

V

IN

C1

V

IN

5

R5
80k

R6
80k

SHDN

4

A1

+

L1

ENABLE

C3

SW

1

L2

D1

V

OUT

C2

–

Q1

V

OUT

R1

NFB

3

R2

* 12mV FOR LT1617-1

Q2
X10

R3
60k

R4
280k

400ns

ONE-SHOT

RESET

Q3

DRIVER

+

0.12Ω

42mV*

A2

–

GND

2

1617/-1 BD

Figure 1. LT1617 Block Diagram

U

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 one­shot, 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 one­shot. 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).

4

LT1617/LT1617-1

U

WUU

APPLICATIO S I FOR ATIO

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 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]
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 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:

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 VIN such as battery powered applications, use the
minimum VIN value in the equation below.

VV V

−+

OUT

L

=

IN MIN

()

I

LIM

D

t

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:



VV

OUT D

2

L

=




I

LIM





+

t



OFF





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

= 400ns.

OFF

= 350mA or

LIM

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 induc-

5

LT1617/LT1617-1

U

WUU

APPLICATIO S I FOR ATIO

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 over­shoot 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
I

is kept below 700mA for the LT1617 and below

PEAK

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 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 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 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 100pF feed-forward ca­pacitor 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.

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

TYPICAL APPLICATIO S

LT1617/LT1617-1

5V to –5V Inverting Converter

L1

V

IN

5V

C1

4.7µF

C1: TAIYO YUDEN LMK316BJ475 [phone]
C2: TAIYO YUDEN JMK316BJ106 [phone]
C3: TAIYO YUDEN EMK212BJ474 [phone]
L1, L2: MURATA LQH3C100K24 [phone]
D1: MOTOROLA MBR0520 [phone]

10µH

V

IN

LT1617

43

SHDN

GND

C3

0.47µF

15

SW

NFB

2

–33V Inverting Charge Pump Converter

L1

V

IN

5V

C1

4.7µF

10µH

15

V

IN

43

SHDN

SW

LT1617

NFB

GND

2

D1

C3

0.22µF

L2

10µH

–5V
100mA

100pF

73.2k

24.9k

D2

D1

619k

24.9k

C2
10µF

1617/-1 TA02

–33V
20mA

C2
1µF

C1: TAIYO YUDEN LMK316BJ475 [phone]
C2: TAIYO YUDEN GMK316BJ105 [phone]
C3: TAIYO YUDEN GMK212BJ224 [phone]
L1: MURATA LQH3C100K24 [phone]
D1: MOTOROLA MBR0540 [phone]

1617/-1 TA03

1-Cell to –9V Inverting Converter

L1

V

IN

1V TO 1.5V

C1

4.7µF

C1: TAIYO YUDEN LMK316BJ475 [phone]
C2: TAIYO YUDEN EMK316BJ475 [phone]
C3: TAIYO YUDEN TMK316BJ224 [phone]
L1, L2: MURATA LQH3C470K34 [phone]
D1: CENTRAL SEMICONDUCTOR CMDSH-3 [phone]

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

47µH

V

IN

LT1617-1

43

SHDN

GND

C3

0.22µF

15

SW

NFB

2

D1

L2

47µH

–9V

2.5mA

150k

C2

4.7µF

24.9k

1617/-1 TA02

However, no

7

LT1617/LT1617-1

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

C5

1µF

L1

10µH

V

IN

LT1617

43

SHDN

C1

4.7µF

GND

2

C4

1µF

15

SW

NFB

D2

D1

100pF

D4

267k

24.9k

U

Dimensions in millimeters (inches) unless otherwise noted.

20V
4mA

C3
1µF

–20V
4mA

C2
1µF

1617/-1 TA04

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)

0.10 – 0.60

(0.004 – 0.024)

REF

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)

S5 SOT-23 0797

2.80 – 3.00

(0.110 – 0.118)

(NOTE 3)

(0.074)

1.90

REF

0.95

(0.037)

REF

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT1307 Single-Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 75mA from One Cell, MSOP Package
LT1316 Burst ModeTM Operation DC/DC with Programmable Current Limit 1.5V Minimum, Precise Control of Peak Current Limit
LT1317 2-Cell Micropower DC/DC with Low-Battery Detector 3.3V at 200mA from Two Cells, 600kHz Fixed Frequency
LT1610 Single-Cell Micropower DC/DC Converter 3V at 30mA fro 1V, 1.7MHz Fixed Frequency
LT1611 1.4MHz Inverting Switching Regulator in 5-Lead SOT-23 – 5V at 150mA from 5V Input, Tiny SOT-23 Package
LT1613 1.4MHz Switching Regulator in 5-Lead SOT-23 5V at 200mA from 3.3V Input, Tiny SOT-23 Package
LT1615 Micropower DC/DC Converter in 5-Lead SOT-23 20V 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

16171f LT/TP 0200 4K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1999