LINEAR TECHNOLOGY LT1932 Technical data

FEATURES

LT1932

Constant-Current DC/DC

LED Driver in ThinSOT

U

DESCRIPTIO

■

Up to 80% Efficiency

■

Inherently Matched LED Current

■

Adjustable Control of LED Current

■

Drives Five White LEDs from 2V

■

Drives Six White LEDs from 2.7V

■

Drives Eight White LEDs from 3V

■

Disconnects LEDs In Shutdown

■

1.2MHz Fixed Frequency Switching

■

Uses Tiny Ceramic Capacitors

■

Uses Tiny 1mm-Tall Inductors

■

Regulates Current Even When VIN > V

■

Operates with VIN as Low as 1V

■

Low Profile (1mm) ThinSOTTM Package

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APPLICATIO S

■

Cellular Telephones

■

Handheld Computers

■

Digital Cameras

■

Portable MP3 Players

■

Pagers

OUT

The LT®1932 is a fixed frequency step-up DC/DC converter
designed to operate as a constant-current source. Be­cause it directly regulates output current, the LT1932 is
ideal for driving light emitting diodes (LEDs) whose light
intensity is proportional to the current passing through
them, not the voltage across their terminals.

With an input voltage range of 1V to 10V, the device works
from a variety of input sources. The LT1932 accurately
regulates LED current even when the input voltage is
higher than the LED voltage, greatly simplifying battery­powered designs. A single external resistor sets LED
current between 5mA and 40mA, which can then be easily
adjusted using either a DC voltage or a pulse width
modulated (PWM) signal. When the LT1932 is placed in
shutdown, the LEDs are disconnected from the output,
ensuring a quiescent current of under 1µA for the entire
circuit. The device’s 1.2MHz switching frequency permits
the use of tiny, low profile chip inductors and capacitors to
minimize footprint and cost in space-conscious portable
applications.

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

ThinSOT is a trademark of Linear Technology Corporation.

TYPICAL APPLICATIO

Li-Ion Driver for Four White LEDs Efficiency

L1

V

2.7V TO 4.2V

IN

C1

4.7µF

PWM
DIMMING
CONTROL

C1: TAIYO YUDEN JMK212BJ475
C2: TAIYO YUDEN EMK212BJ105
D1:ZETEX ZHCS400
L1: SUMIDA CLQ4D106R8 OR PANASONIC ELJEA6R8

6.8µH

61

V

IN

LT1932

SHDN

R

SET

4

R

SET

1.50k

SW

GND

LED

2

U

D1

35

15mA

C2
1µF

1932 TA01

85

80

75

70

EFFICIENCY (%)

65

60

55

0

VIN = 4.2V

VIN = 2.7V

5101520

LED CURRENT (mA)

1932 TA02

1932f

1

LT1932

WWWU

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

UU

W

(Note 1)

VIN Voltage ............................................................. 10V

SHDN Voltage ......................................................... 10V

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

LED Voltage ............................................................. 36V

R

Voltage ............................................................. 1V

SET

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

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

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

TOP VIEW

SW 1

GND 2

LED 3

S6 PACKAGE

6-LEAD PLASTIC SOT-23

T

= 125°C, θJA = 250°C/ W

JMAX

6 V

IN

5 SHDN
4 R

SET

ORDER PART

NUMBER

LT1932ES6

S6 PART MARKING

LTST

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

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

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

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Input Voltage 1V
Quiescent Current V

V

R

Pin Voltage R

SET

LED Pin Voltage R
LED Pin Current R

R
R

R
LED Pin Current Temperature Coefficient I
Switching Frequency VIN = 1V 0.8 1.2 1.6 MHz
Maximum Switch Duty Cycle ● 90 95 %
Switch Current Limit 400 550 780 mA
Switch V

CESAT

SHDN Pin Current V

Start-Up Threshold (SHDN Pin) 0.85 V
Shutdown Threshold (SHDN Pin) 0.25 V

Switch Leakage Current Switch Off, VSW = 5V 0.01 5 µA

LED

ISW = 300mA 150 200 mV

V

The ● denotes specifications that apply over the full operating temperature

= 1.2V, unless otherwise noted.

SHDN

= 0.2V 1.2 1.6 mA

RSET

= 0V 0.1 1.0 µA

SHDN

= 1.50k 100 mV

SET

= 1.50k, VIN < V

SET

= 562Ω, VIN = 1.5V 33 38 45 mA

SET

= 750Ω, VIN = 1.2V 25 30 36 mA

SET

= 1.50k, VIN = 1.2V 12.5 15 17.5 mA

SET

= 4.53k, VIN = 1.2V 5 mA

SET

= 15mA –0.02 mA/°C

= 0V 0 0.1 µA

SHDN

= 2V 15 30 µA

SHDN

(Figure 1) 120 180 mV

OUT

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

a device may be impaired.

Note 2: The LT1932E is 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.

2

1932f

UW

INPUT VOLTAGE (V)

0

LED CURRENT (mA)

35

6

1932 G06

20

10

24

5
0

40

45

50

30
25

15

810

R

SET

= 750Ω

R

SET

= 562Ω

R

SET

= 1.50k

R

SET

= 4.53k

TYPICAL PERFOR A CE CHARACTERISTICS

LT1932

Switch Saturation Voltage (V

400

350

300

250

200

150

100

50

SWITCH SATURATION VOLTAGE (mV)

0

100 200 400

0

SWITCH CURRENT (mA)

TJ = 125°C

TJ = 25°C

300

TJ = –50°C

CESAT

500

1932 G01

600

)

Switch Current Limit Switching Frequency

700

600

500

400

300

PEAK CURRENT (mA)

200

100

0

–50

LED Pin Voltage LED Current

400

350

300

250

200

TJ = 25°C

150

LED PIN VOLTAGE (mV)

100

50

0

510 20

0

LED CURRENT (mA)

TJ = 125°C

15 25

T

= –50°C

J

4030 35

1932 G04

50
45
40
35
30
25
20

LED CURRENT (mA)

15
10

5
0

–50

VIN = 1.2V

VIN = 10V

50 100 125

–25 0

–25 0 50

25 75

TEMPERATURE (°C)

R

= 562Ω

SET

R

= 750Ω

SET

R

= 1.50k

SET

R

= 4.53k

SET

25

TEMPERATURE (°C)

1932 G02

75 100 125

1932 G05

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

SWITCHING FREQUENCY (MHz)

0.2
0

–50

–25

25

0

TEMPERATURE (°C)

LED Current

VIN = 10V

VIN = 1.2V

50

100

125

1932 G03

75

2.00

1.75

1.50

1.25

1.00

0.75

0.50

QUIESCENT CURRENT (mA)

0.25

Quiescent Current SHDN Pin Current

50
45
40

0

–25 0 50

–50

VIN = 10V

VIN = 1.2V

25

TEMPERATURE (°C)

75 100 125

1932 G07

35

30
25

20

SHDN PIN CURRENT

15
10

5
0

2

0

SHDN PIN VOLTAGE (V)

Switching Waveforms

V

= –50°C

T

J

TJ = 25°C

TJ = 125°C

6

8

4

10

1932 G08

SW

10V/DIV

I

200mA/DIV

V

OUT

20mV/DIV

AC COUPLED

I

LED

10mA/DIV

L1

VIN = 3V 0.5µs/DIV
4 WHITE LEDs
I

= 15mA

LED

CIRCUIT ON FIRST PAGE
OF THIS DATA SHEET

1093 G09

1932f

3

LT1932

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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 Pin. Tie this pin directly to local

ground plane.

LED (Pin 3): LED Pin. This is the collector of the internal

NPN LED switch. Connect the cathode of the bottom LED
to this pin.

W

BLOCK DIAGRA

V

IN

SHDN

C1

5

DRIVER

S

Q

R

L1

V

IN

6

1

Q1

0.04Ω

1.2MHz

OSCILLATOR

SW

+

×5

–

R

(Pin 4): A resistor between this pin and ground

SET

programs the LED current (that flows into the LED pin).
This pin is also used to provide LED dimming.

SHDN (Pin 5): Shutdown Pin. Tie this pin higher than

0.85V to turn on the LT1932; tie below 0.25V to turn it off.

VIN (Pin 6): Input Supply Pin. Bypass this pin with a

capacitor to ground as close to the device as possible.

D1

+

Σ

+

+

A2

–

DRIVER

–

A1

+

V

OUT

C2

LED

3

I

Q2

LED

2

GND

Figure 1. LT1932 Block Diagram

U

OPERATIO

The LT1932 uses a constant frequency, current mode
control scheme to regulate the output current, I
Operation can be best understood by referring to the
block diagram in Figure 1. At the start of each oscillator
cycle, the SR latch is set, turning on power switch Q1. The
signal at the noninverting input of the PWM comparator
A2 is proportional to the switch current, summed to­gether with a portion of the oscillator ramp. When this
signal reaches the level set by the output of error amplifier
A1, comparator A2 resets the latch and turns off the

LED

.

LED CURRENT

REFERENCE

4

R

SET

I

SET

R

SET

1932 F01

power switch. In this manner, A1 sets the correct peak
current level to keep the LED current in regulation. If A1’s
output increases, more current is delivered to the output;
if it decreases, less current is delivered. A1 senses the
LED current in switch Q2 and compares it to the current
reference, which is programmed using resistor R
R

pin is regulated to 100mV and the output current,

SET

I

, is regulated to 225 • I

LED

. Pulling the R

SET

SET

. The

SET

pin higher
than 100mV will pull down the output of A1, turning off
power switch Q1 and LED switch Q2.

1932f

4

WUUU

APPLICATIO S I FOR ATIO

LT1932

Inductor Selection

Several inductors that work well with the LT1932 are listed
in Table 1. Many different sizes and shapes are available.
Consult each manufacturer for more detailed information
and for their entire selection of related parts. As core
losses at 1.2MHz are much lower for ferrite cores that for
the cheaper powdered-iron ones, ferrite core inductors
should be used to obtain the best efficiency. Choose an
inductor that can handle at least 0.5A and ensure that the
inductor has a low DCR (copper wire resistance) to mini­mize I2R power losses. A 4.7µH or 6.8µH inductor will be
a good choice for most LT1932 designs.

Table 1. Recommended Inductors

MAX MAX

L DCR HEIGHT

PART (µH) (mΩ) (mm) VENDOR

ELJEA4R7 4.7 180 2.2 Panasonic
ELJEA6R8 6.8 250 2.2 [phone]

www.panasonic.com

LQH3C4R7M24 4.7 260 2.2 Murata
LQH3C100M24 10 300 2.2 [phone]

www.murata.com

LB2016B4R7 4.7 250 1.6 Taiyo Yuden
LB2016B100 6.8 350 1.6 [phone]

www.t-yuden.com

CMD4D06-4R7 4.7 216 0.8 Sumida
CMD4D06-6R8 6.8 296 0.8 [phone]
CLQ4D10-4R7 4.7 162 1.2 www.sumida.com
CLQ4D10-6R8 6.8 195 1.2

efficiency by up to 12% over the smaller, thinner ones.
Keep this in mind when choosing an inductor.

The value of inductance also plays an important role in the
overall system efficiency. While a 1µH inductor will have
a lower DCR and a higher current rating than the 6.8µH
version of the same part, lower inductance will result in
higher peak currents in the switch, inductor and diode.
Efficiency will suffer if inductance is too small. Figure 3
shows the efficiency of the Typical Application on the front
page of this data sheet, with several different values of the
same type of inductor (Panasonic ELJEA). The smaller
values give an efficiency 3% to 5% lower than the 6.8µH
value.

85

PANASONIC

80

75

70

EFFICIENCY (%)

65

60

55

SUMIDA

CLQ4D10-6R8

TAIYO YUDEN

LB2016B6R8

0

TAIYO YUDEN

LB2012B6R8

5101520

LED CURRENT (mA)

Figure 2. Efficiency for Several Different Inductor Types

ELJEA6R8

SUMIDA

CMD4D06-6R8

VIN = 3.6V
4 WHITE LEDs
ALL ARE 10µH
INDUCTORS

1932 F02

Inductor Efficiency Considerations

Many applications have thickness requirements that re­strict component heights to 1mm or 2mm. There are 2mm
tall inductors currently available that provide a low DCR
and low core losses that help provide good overall effi­ciency. Inductors with a height of 1mm (and less) are
becoming more common, and a few companies have
introduced chip inductors that are not only thin, but have
a very small footprint as well. While these smaller induc­tors will be a necessity in some designs, their smaller size
gives higher DCR and core losses, resulting in lower
efficiencies. Figure 2 shows efficiency for the Typical
Application circuit on the front page of this data sheet, with
several different inductors. The larger devices improve

85

80

75

4.7µH

70

EFFICIENCY (%)

65

60

55

0

22µH

6.8µH

2.2µH

VIN = 3.6V
4 WHITE LEDs
PANASONIC ELJEA
INDUCTORS

5101520

LED CURRENT (mA)

1932 F03

Figure 3. Efficiency for Several Different Inductor Values

1932f

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