LT1937ES5#PBF [Linear]
LT1937 - White LED Step-Up Converter in SC70 and ThinSOT; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C;
| 型号： | LT1937ES5#PBF |
| 厂家： | 
Linear |
| 描述： | LT1937 - White LED Step-Up Converter in SC70 and ThinSOT; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C 开关 光电二极管 |
| 文件： | 总12页 (文件大小：355K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1937
White LED
Step-Up Converter in
SC70 and ThinSOT
U
FEATURES
DESCRIPTIO
The LT®1937 is a step-up DC/DC converter specifically
designed to drive white LEDs with a constant current. The
device can drive two, three or four LEDs in series from a
Li-Ion cell. Series connection of the LEDs provides iden-
tical LED currents resulting in uniform brightness and
eliminating the need for ballast resistors. The LT1937
switches at 1.2MHz, allowing the use of tiny external
components. The output capacitor can be as small as
0.22µF, saving space and cost versus alternative solu-
tions. A low 95mV feedback voltage minimizes power loss
in the current setting resistor for better efficiency.
■
Inherently Matched LED Current
■
High Efficiency: 84% Typical
■
Drives Up to Four LEDs from a 3.2V Supply
■
Drives Up to Six LEDs from a 5V Supply
■
36V Rugged Bipolar Switch
■
Fast 1.2MHz Switching Frequency
■
Uses Tiny 1mm Tall Inductors
■
Requires Only 0.22µF Output Capacitor
Low Profile SC70 and ThinSOTTM Packaging
■
U
APPLICATIO S
The LT1937 is available in low profile SC70 and ThinSOT
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
■
Cellular Phones
■
PDAs, Handheld Computers
■
Digital Cameras
■
MP3 Players
■
GPS Receivers
U
TYPICAL APPLICATIO
Conversion Efficiency
L1
22µH
90
D1
V
IN
3V TO 5V
85
80
C1
C2
LED 1
LED 2
LED 3
1µF
0.22µF
V
SW
FB
IN
15mA
V
IN
= 3V
V
IN
= 3.6V
LT1937
75
70
65
60
OFF ON
SHDN
GND
R1
6.34Ω
1937 F01a
C1, C2: X5R OR X7R DIELECTRIC
D1: CENTRAL SEMICONDUCTOR CMDSH-3
L1: MURATA LQH3C-220 OR EQUIVALENT
0
5
10
LED CURRENT (mA)
15
20
Figure 1. Li-Ion Powered Driver for Three White LEDs
1937 TA01b
1937f
1
LT1937
W W
U W
ABSOLUTE AXI U RATI GS (Note 1)
Input Voltage (VIN) ................................................. 10V
SW Voltage ............................................................. 36V
FB Voltage .............................................................. 10V
SHDN Voltage ......................................................... 10V
Extended Commercial
Operating Temperature Range (Note 2)... –40°C to 85°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
U W
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
TOP VIEW
TOP VIEW
SW 1
GND 2
FB 3
5 V
IN
LT1937ES5
LT1937ESC6
SW 1
GND 2
FB 3
6 V
IN
5 GND
4 SHDN
4 SHDN
S5 PACKAGE
S5 PART MARKING
LTYN
SC6 PART MARKING
LAAB
SC6 PACKAGE
5-LEAD PLASTIC TSOT-23
6-LEAD PLASTIC SC70
TJMAX = 125°C, θJA = 256°C/ W IN FREE AIR
θJA = 120°C ON BOARD OVER GROUND PLANE
TJMAX = 125°C, θJA = 256°C/ W IN FREE AIR
θJA = 150°C ON BOARD OVER GROUND PLANE
Consult LTC Marketing for parts specified with wider operating temperature ranges.
TA = 25°C, VIN = 3V, VSHDN = 3V, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
Minimum Operating Voltage
Maximum Operating Voltage
Feedback Voltage
2.5
10
V
I
= 100mA, Duty Cycle = 66%
86
10
95
45
104
100
mV
nA
SW
FB Pin Bias Current
Supply Current
1.9
0.1
2.5
1.0
mA
µA
SHDN = 0V
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
0.8
85
1.2
90
1.6
MHz
%
320
350
0.01
mA
mV
µA
V
Switch V
I
= 250mA
= 5V
CESAT
SW
Switch Leakage Current
SHDN Voltage High
SHDN Voltage Low
V
5
SW
1.5
0.4
V
SHDN Pin Bias Current
65
µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: The LT1937E 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.
1937f
2
LT1937
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Switching Frequency
Quiescent Current
SHDN Pin Bias Current
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
400
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–50°C
350
300
100°C
25°C
SHDN = 10V
250
200
150
100
50
SHDN = 3.6V
SHDN = 2.7V
SHDN = 3V
0
0
2
4
6
8
10
–25
0
50
75
100
50
TEMPERATURE (°C)
100
–50
25
–50
–25
0
25
75
V
IN
(V)
TEMPERATURE (°C)
1937 G01
1937 G02
1937 G03
Feedback Bias Current
Efficiency vs Temperature
Current Limit vs Duty Cycle
350
300
250
200
150
100
50
60
50
40
30
85
V
= 3.6V
IN
3 LEDs
I
= 20mA
LED
84
83
82
81
80
I
I
= 15mA
= 10mA
LED
LED
20
10
0
0
20
40
DUTY CYCLE (%)
80
100
0
60
50
100
–50
–25
0
25
75
–50
0
50
TEMPERATURE (°C)
100
TEMPERATURE (°C)
1937 G06
1937 G04
1937 G05
U
U
U
PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor/diode here.
Minimize trace area at this pin to reduce EMI.
SHDN (Pin 4):Shutdown Pin. Connect to 1.5Vor higher to
enable device; 0.4V or less to disable device.
GND (Pin 2): Ground Pin. Connect directly to local ground
plane.
GND (Pin 5, SC70 Package): Ground Pin. Connect to Pin
2 and to local ground plane
FB (Pin 3): Feedback Pin. Reference voltage is 95mV.
Connect cathode of lowest LED and resistor here. Calcu-
late resistor value according to the formula:
VIN (Pin 5/Pin 6 SC70 Package): Input Supply Pin. Must
be locally bypassed.
RFB = 95mV/ILED
1937f
3
LT1937
W
BLOCK DIAGRA
V
IN
FB
3
(PIN 6 FOR
SC70 PACKAGE)
5
1
SW
–
+
COMPARATOR
A2
–
+
A1
DRIVER
95mV
V
REF
Q1
R
Q
R
C
1.25V
S
C
C
+
–
0.2Ω
Σ
RAMP
GENERATOR
SHDN
4
(PINS 2 AND 5 FOR
SC70 PACKAGE)
SHUTDOWN
2
GND
1937 BD1
1.2MHz
OSCILLATOR
Figure 2. LT1937 Block Diagram
U
OPERATIO
pulses. This will result in some low frequency ripple,
althoughtheLED currentremainsregulatedonanaverage
basis down to zero. The photo in Figure 3 details circuit
operation driving three white LEDs at a 4mA load. Peak
inductor current is less than 50mA and the regulator
operates in discontinuous mode, meaning the inductor
current reaches zero during the discharge phase. After the
inductor current reaches zero, the switch pin exhibits
ringing due to the LC tank circuit formed by the inductor
in combination with switch and diode capacitance. This
ringingisnotharmful;farlessspectralenergyiscontained
in the ringing than in the switch transitions. The ringing
can be damped by application of a 300Ω resistor across
the inductor, although this will degrade efficiency.
The LT1937 uses a constant frequency, current mode
control scheme to provide excellent line and load regula-
tion. Operation can be best understood by referring to the
block diagram in Figure 2. At the start of each oscillator
cycle, the SR latch is set, which turns on the power switch
Q1. A voltage proportional to the switch current is added
to a stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator A2. When this
voltageexceedsthelevelatthenegativeinputofA2,theSR
latch is reset turning off the power switch. The level at the
negative input of A2 is set by the error amplifier A1, and is
simply an amplified version of the difference between the
feedback voltage and the reference voltage of 95mV. In
this manner, the error amplifier sets the correct peak
current level to keep the output in regulation. If the error
amplifier’s output increases, more current is delivered to
the output; if it decreases, less current is delivered.
VSW
5V/DIV
Minimum Output Current
IL2
The LT1937 can regulate three series LEDs connected at
low output currents, down to approximately 4mA from a
4.2V supply, without pulse skipping, using the same
external components as specified for 15mA operation. As
current is further reduced, the device will begin skipping
50mA/DIV
VOUT
100mV/DIV
0.2µs/DIV
1937 F03
Figure 3. Switching Waveforms at ILED = 4mA, VIN = 3.6V
1937f
4
LT1937
W U U
APPLICATIO S I FOR ATIO
U
Capacitor Selection
Inductor Selection
The small size of ceramic capacitors makes them ideal for
LT1937 applications. X5R and X7R types are recom-
mended because they retain their capacitance over wider
voltage and temperature ranges than other types such as
Y5V or Z5U. A 1µF input capacitor and a 0.22µF output
capacitor are sufficient for most LT1937 applications.
A 22µH inductor is recommended for most LT1937 appli-
cations. Although small size and high efficiency are major
concerns, the inductor should have low core losses at
1.2MHz and low DCR (copper wire resistance). Some
inductors in this category with small size are listed in
Table 1. The efficiency comparison of different inductors
is shown in Figure 4.
Table 2. Recommended Ceramic Capacitor Manufacturers
Table 1. Recommended Inductors
CURRENT
MANUFACTURER
Taiyo Yuden
AVX
PHONE
URL
408-573-4150
843-448-9411
814-237-1431
408-986-0424
www.t-yuden.com
www.avxcorp.com
www.murata.com
www.kemet.com
DCR
(Ω)
RATING
(mA)
PART NUMBER
MANUFACTURER
Murata
LQH3C220
0.71
4.0
250
160
350
75
Murata
814-237-1431
www.murata.com
Kemet
Diode Selection
ELJPC220KF
Panasonic
714-373-7334
www.panasonic.com
Schottky diodes, with their low forward voltage drop and
fast reverse recovery, are the ideal choices for LT1937
applications. TheforwardvoltagedropofaSchottkydiode
represents the conduction losses in the diode, while the
diode capacitance (CT or CD) represents the switching
losses. For diode selection, both forward voltage drop and
diode capacitance need to be considered. Schottky diodes
with higher current ratings usually have lower forward
voltage drop and larger diode capacitance, which can
cause significant switching losses at the 1.2MHz switch-
ing frequency of the LT1937. A Schottky diode rated at
100mA to 200mA is sufficient for most LT1937 applica-
tions. Some recommended Schottky diodes are listed in
Table 3.
CDRH3D16-220
LB2012B220M
LEM2520-220
0.53
1.7
Sumida
847-956-0666
www.Sumida.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
5.5
125
Taiyo Yuden
408-573-4150
www.t-yuden.com
90
85
80
75
70
65
60
55
50
V
= 3.6V
IN
3LEDs
Table 3. Recommended Schottky Diodes
FORWARD VOLTAGE
CURRENT DROP CAPACITANCE
DIODE
PART
NUMBER
(mA)
(V)
0.58 at
100mA
(pF)
7.0 at
10V
MANUFACTURER
Central
631-435-1110
www.centralsemi.com
Central
631-435-1110
www.centralsemi.com
Zetex
631-543-7100
www.zetex.com
MURATA LQH3C-220
CMDSH-3
CMDSH2-3
BAT54
100
PANASONIC ELJPC220KF
SUMIDA CDRH3D16-220
TAIYO YUDEN LB2012B220M
TAIYO YUDEN LEM2520-220
200
200
0.49 at
200mA
15 at
10V
0
2
4
6
8
10 12 14 16 18 20
LOAD CURRENT (mA)
1937 F04
0.53 at
100mA
10 at
25V
Figure 4. Efficiency Comparison of Different Inductors
1937f
5
LT1937
W U U
U
APPLICATIO S I FOR ATIO
LED Current Control
Dimming Control
The LED current is controlled by the feedback resistor (R1
in Figure 1). The feedback reference is 95mV. The LED
currentis95mV/R1.InordertohaveaccurateLEDcurrent,
precision resistors are preferred (1% is recommended).
The formula and table for R1 selection are shown below.
There are four different types of dimming control circuits:
1. Using a PWM Signal to SHDN Pin
With the PWM signal applied to the SHDN pin, the LT1937
is turned on or off by the PWM signal. The LEDs operate
at either zero or full current. The average LED current
increases proportionally with the duty cycle of the PWM
signal. A 0% duty cycle will turn off the LT1937 and
corresponds to zero LED current. A 100% duty cycle
corresponds to fullcurrent. Thetypical frequency rangeof
the PWM signal is 1kHz to 10kHz. The magnitude of the
PWM signal should be higher than the minimum SHDN
voltage high. The switching waveforms of the SHDN pin
PWM control are shown in Figures 6a and 6b.
R1 = 95mV/ILED
(1)
Table 4. R1 Resistor Value Selection
I
(mA)
R1 (Ω)
19.1
LED
5
10
12
15
20
9.53
7.87
6.34
4.75
Open-Circuit Protection
LT1937
SHDN
In the cases of output open circuit, when the LEDs are
disconnected from the circuit or the LEDs fail, the feed-
back voltage will be zero. The LT1937 will then switch at
a high duty cycle resulting in a high output voltage, which
may cause the SW pin voltage to exceed its maximum 36V
rating. A zener diode can be used at the output to limit the
voltage on the SW pin (Figure 5). The zener voltage should
be larger than the maximum forward voltage of the LED
string.Thecurrentratingofthezenershouldbelargerthan
0.1mA.
PWM
FB
100mV/DIV
SHDN
2V/DIV
200µs/DIV
1937 F06a
(6a) 1kHz
L
D
22µH
V
IN
FB
C
C
OUT
0.22µF
IN
100mV/DIV
1µF
V
SW
FB
IN
R2
1k
LT1937
SHDN
2V/DIV
SHDN
GND
R1
6.34Ω
20µs/DIV
1937 F06b
1937 F05
(6b) 10kHz
Figure 5. LED Driver with Open-Circuit Protection
Figure 6. PWM Dimming Control Using the SHDN Pin
1937f
6
LT1937
W U U
APPLICATIO S I FOR ATIO
U
2. Using a DC Voltage
4. Using a Logic Signal
Forsomeapplications,thepreferredmethodofbrightness
control is a variable DC voltage to adjust the LED current.
The dimming control using a DC voltage is shown in
Figure 7. As the DC voltage increases, the voltage drop on
R2 increases and the voltage drop on R1 decreases. Thus,
the LED current decreases. The selection of R2 and R3 will
make the current from the variable DC source much
smaller than the LED current and much larger than the FB
pinbiascurrent.ForVDC rangefrom0Vto2V,theselection
of resistors in Figure 7 gives dimming control of LED
current from 0mA to 15mA.
For applications that need to adjust the LED current in
discrete steps, a logic signal can be used as shown in
Figure 9. R1 sets the minimum LED current (when the
NMOS is off). RINC sets how much the LED current
increases when the NMOS is turned on. The selection of
R1 and RINC follows formula (1) and Table 4.
Start-up and Inrush Current
To achieve minimum start-up delay, no internal soft-start
circuit is included in LT1937. When first turned on without
anexternalsoft-startcircuit,inrushcurrentisabout200mA
as shown in Figure 10. If soft-start is desired, the recom-
mendedcircuitandthewaveformsareshowninFigure11.
If both soft-start and dimming are used, a 10kHz PWM
signal on SHDN is not recommended. Use a lower fre-
quency or implement dimming through the FB pin as
shown in Figures 7, 8 or 9.
3. Using a Filtered PWM Signal
The filtered PWM signal can be considered as an adjust-
able DC voltage. It can be used to replace the variable DC
voltage source in dimming control. The circuit is shown in
Figure 8.
LT1937
FB
LT1937
FB
R3
90k
R2
5k
R
INC
V
DC
LOGIC
SIGNAL
R1
6.3Ω
2N7002
R1
1937 F09
1937 F07
Figure 7. Dimming Control Using a DC Voltage
Figure 9. Dimming Control Using a Logic Signal
IIN
100mA/DIV
LT1937
FB
FB
100mV/DIV
R3
R2
5k
90k
10k
SHDN
2V/DIV
PWM
R1
6.3Ω
0.1µF
VIN = 3.6V
THREE LEDs
15mA
50µs/DIV
1937 F09
1937 F08
Figure 8. Dimming Control Using a Filtered PWM Signal
Figure 10. Start-Up Waveforms Without Soft-Startup Circuit
1937f
7
LT1937
W U U
U
APPLICATIO S I FOR ATIO
D1
IIN
100mA/DIV
2.2nF
FB
100mV/DIV
R2
1k
D2
LT1937
FB
C
OUT
SHDN
2V/DIV
R1
6.34Ω
5k
VIN = 3.6V
THREE LEDs
15mA
50µs/DIV
1937 F11b
D2: MMBT
1937 F11a
(11a) Recommended Soft-Startup Circuit
(11b) Soft-Startup Waveforms
Figure 11. Recommended Soft-Startup Circuit and Waveforms
area of all traces connected to the SW pin and always use
a ground plane under the switching regulator to minimize
interplanecoupling.Inaddition,thegroundconnectionfor
the feedback resistor R1 should be tied directly to the GND
pin and not shared with any other component, ensuring a
clean, noise-free connection. Recommended component
placement is shown in Figure 12.
Board Layout Consideration
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
Tomaximizeefficiency, switchriseandfalltimesaremade
as short as possible. To prevent electromagnetic interfer-
ence (EMI) problems, proper layout of the high frequency
switching path is essential. The voltage signal of the SW
pin has sharp rise and fall edges. Minimize the length and
L
L
V
IN
V
IN
D
D
C
C
IN
1
2
3
6
5
4
C
C
IN
1
2
3
5
4
O
O
GND
GND
SHDN
SHDN
R2
R2
R1
R1
1937 F12b
1937 F12a
DIMMING
CONTROL
DIMMING
CONTROL
R3
R3
(SOT-23 Package)
(SC70 Package)
Figure 12. Recommended Component Placement
1937f
8
LT1937
U
TYPICAL APPLICATIO S
Li-Ion to Two White LEDs
Two LED Efficiency
86
84
82
80
78
76
74
72
70
L
D
22µH
V
= 3.6V
IN
V
IN
3V TO 5V
C
C
OUT
IN
1µF
1µF
V
IN
= 3V
V
DC
DIMMING
V
SW
FB
IN
90k
LT1937
5k
SHDN
GND
R1
2Ω
C
C
: TAIYO YUDEN JMK107BJ105
: AVX 0603ZD105
D: CENTRAL CMDSH2-3
L: MURATA LQH3C220
IN
1937 TA05a
20
LED CURRENT (mA)
0
10
30
40
OUT
1937 TA05a
Li-Ion to Three White LEDs
Three LED Efficiency
90
85
L
D
22µH
V
IN
3V TO 5V
C
C
OUT
IN
1µF
0.22µF
V
DC
DIMMING
80
75
V
IN
= 3V
V
IN
= 3.6V
V
SW
FB
IN
90k
LT1937
SHDN
GND
5k
70
65
60
R1
4Ω
C
C
: TAIYO YUDEN JMK107BJ105
: AVX 0603YD224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
IN
1937 TA01a
0
5
10
LED CURRENT (mA)
15
20
OUT
1937 TA01b
1937f
9
LT1937
U
TYPICAL APPLICATIO S
Li-Ion to Five White LEDs
Five LED Efficiency
85
80
75
70
L
D
22µH
V
IN
3V TO 5V
C
C
OUT
0.22µF
IN
1µF
V
DC
DIMMING
V
= 3V
IN
V
SW
FB
IN
90k
LT1937
V
IN
= 3.6V
5k
SHDN
GND
R1
4Ω
65
C
C
: TAIYO YUDEN JMK107BJ105
OUT
IN
1937 TA03a
0
2
4
6
8
10
12
: TAIYO YUDEN GMK212BJ224
LOAD CURRENT (mA)
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
1937 TA03b
Seven LED Efficiency
5V to Seven White LEDs
85
80
75
70
L
D
22µH
V
IN
5V
C
C
IN
OUT
1µF
0.22µF
V
DC
DIMMING
V
IN
SW
FB
90k
LT1937
5k
SHDN
GND
R1
4Ω
65
C
C
: TAIYO YUDEN JMK107BJ105
OUT
IN
1937 TA04a
0
5
10
15
: TAIYO YUDEN GMK212BJ224
LOAD CURRENT (mA)
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
1937 TA04b
1937f
10
LT1937
U
PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
0.62
MAX
0.95
REF
2.90 BSC
(NOTE 4)
1.22 REF
1.50 – 1.75
(NOTE 4)
2.80 BSC
1.4 MIN
3.85 MAX 2.62 REF
PIN ONE
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
DATUM ‘A’
0.01 – 0.10
1.00 MAX
0.30 – 0.50 REF
1.90 BSC
0.09 – 0.20
(NOTE 3)
NOTE:
S5 TSOT-23 0302
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
SC6 Package
6-Lead Plastic SC70
(Reference LTC DWG # 05-08-1638)
0.47
MAX
0.65
REF
1.80 – 2.20
(NOTE 4)
1.16 REF
INDEX AREA
(NOTE 6)
1.15 – 1.35
(NOTE 4)
1.80 – 2.40
0.96 MIN
3.26 MAX 2.1 REF
PIN 1
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.15 – 0.30
6 PLCS (NOTE 3)
0.65 BSC
0.10 – 0.40
0.80 – 1.00
0.00 – 0.10
1.00 MAX
0.10 – 0.30
SC6 SC70 0302
0.10 – 0.18
(NOTE 3)
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. DETAILS OF THE PIN 1 INDENTIFIER ARE OPTIONAL,
BUT MUST BE LOCATED WITHIN THE INDEX AREA
7. EIAJ PACKAGE REFERENCE IS EIAJ SC-70
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
1937f
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-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LT1937
U
TYPICAL APPLICATIO
Li-Ion to Four White LEDs
L
D
22µH
V
IN
3V TO 5V
C
C
OUT
0.22µF
IN
1µF
V
DC
DIMMING
V
SW
FB
IN
90k
LT1937
SHDN
GND
5k
R1
4Ω
C
C
: TAIYO YUDEN JMK107BJ105
OUT
IN
1937 TA02a
: AVX 0603YD224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
Four LED Efficiency
85
80
75
70
Switching Waveforms
V
SW
10V/DIV
V
= 3V
IN
V
= 3.6V
IN
I
SW
100mA/DIV
V
OUT
100mV/DIV
1937 TA02c
= 3.6V
0.2µs/DIV
V
IN
FOUR LEDs
15mA
60
0
5
10
15
20
LOAD CURRENT (mA)
1937 TA02b
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
Up to 36V Output; 20µA I , V : 1V to 15V,
LT1615
Micropower Step-Up Converter in ThinSOT
Q
IN
Can Drive Up to Six LEDs, ThinSOT Package
LT1618
LT1932
Constant Current/Voltage Step-Up DC/DC
White LED Step-Up Converter in ThinSOT
1.4MHz, Drives Up to 20 LEDs, MS10 Package
1.2MHz, V = 1V to 10V, Drives Up to Eight LEDs from 3V Input,
IN
ThinSOT Package
LT1944/LT1944-1
Dual Micropower Step-Up Converter
V = 1.2V to 15V, Two Independent DC/DCs, Up to 36V , 20µA I ,
IN OUT Q
MS10 Package
LTC®3200/LTC3200-5 Low Noise White LED Charge Pump Converter
For up to 6 LEDs
2MHz, 100mA, No Inductor Required, MS8/ThinSOT Packages
LTC3201
Ultralow Noise White LED Charge Pump Converter
For up to 6 LEDs
1.8MHz, 100mA, No Inductor Required, DAC Brightness Adj,
MS8 Package
LTC3202
Low Noise White LED Fractional Charge Pump Converter
For up to 6 LEDs
1.5MHz, 125mA, No Inductor Required, Digital Brightness Adjust,
MS8 Package
1937f
LT/TP 0702 2K • PRINTED IN USA
12 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2002
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