LINER LT1937 White led step-up converter in sc70 and thinsot Datasheet

LT1937
White LED
Step-Up Converter in
SC70 and ThinSOT
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FEATURES
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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 identical 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 solutions. 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
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APPLICATIO S
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The LT1937 is available in low profile SC70 and ThinSOT
packages.
Cellular Phones
PDAs, Handheld Computers
Digital Cameras
MP3 Players
GPS Receivers
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
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TYPICAL APPLICATIO
Conversion Efficiency
L1
22µH
D1
C1
1µF
VIN
SW
LT1937
OFF ON
SHDN
GND
85
C2
0.22µF
LED 1
EFFICIENCY (%)
VIN
3V TO 5V
90
15mA
LED 2
LED 3
FB
R1
6.34Ω
1937 F01a
C1, C2: X5R OR X7R DIELECTRIC
D1: CENTRAL SEMICONDUCTOR CMDSH-3
L1: MURATA LQH3C-220 OR EQUIVALENT
80
VIN = 3V
70
65
60
0
Figure 1. Li-Ion Powered Driver for Three White LEDs
VIN = 3.6V
75
5
10
15
LED CURRENT (mA)
20
1937 TA01b
1937f
1
LT1937
W W
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ABSOLUTE
RATI GS
Input Voltage (VIN) .................................................
SW Voltage .............................................................
FB Voltage ..............................................................
SHDN Voltage .........................................................
(Note 1)
10V
36V
10V
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
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
SW 1
TOP VIEW
5 VIN
GND 2
FB 3
ORDER PART
NUMBER
LT1937ES5
4 SHDN
SW 1
6 VIN
GND 2
5 GND
FB 3
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
S5 PART MARKING
TJMAX = 125°C, θJA = 256°C/ W IN FREE AIR
θJA = 120°C ON BOARD OVER GROUND PLANE
LTYN
LT1937ESC6
4 SHDN
SC6 PART MARKING
SC6 PACKAGE
6-LEAD PLASTIC SC70
LAAB
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.
ELECTRICAL CHARACTERISTICS
PARAMETER
TA = 25°C, VIN = 3V, VSHDN = 3V, unless otherwise noted.
CONDITIONS
MIN
Minimum Operating Voltage
TYP
UNITS
V
Maximum Operating Voltage
Feedback Voltage
MAX
2.5
ISW = 100mA, Duty Cycle = 66%
FB Pin Bias Current
10
V
86
95
104
mV
10
45
100
nA
1.9
0.1
2.5
1.0
mA
µA
1.6
MHz
Supply Current
SHDN = 0V
Switching Frequency
0.8
1.2
Maximum Duty Cycle
85
90
Switch Current Limit
%
320
mA
Switch VCESAT
ISW = 250mA
350
mV
Switch Leakage Current
VSW = 5V
0.01
SHDN Voltage High
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
µA
1.5
V
SHDN Voltage Low
SHDN Pin Bias Current
5
0.4
65
V
µA
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
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TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
100°C
25°C
1.6
SHDN PIN BIAS CURRENT (µA)
1.8
IQ (mA)
1.4
1.2
1.0
0.8
0.6
0.4
400
1.4
350
1.2
300
SHDN = 10V
250
200
150
SHDN = 3.6V
100
50
0.2
0
0
2
4
6
8
SHDN = 3V
– 25
VIN (V)
0
50
25
TEMPERATURE (°C)
1937 G01
Feedback Bias Current
0.4
0.2
75
0
–50
100
40
30
20
75
100
50
25
0
TEMPERATURE (°C)
75
VIN = 3.6V
3 LEDs
1937 G03
300
ILED = 20mA
83
ILED = 15mA
82
ILED = 10mA
80
–50
100
Current Limit vs Duty Cycle
81
10
–25
350
84
EFFICIENCY (%)
FEEDBACK BIAS CURRENT (nA)
50
50
25
0
TEMPERATURE (°C)
0.6
Efficiency vs Temperature
85
–25
0.8
1937 G02
60
0
–50
1.0
SHDN = 2.7V
0
– 50
10
SWITCHING FREQUENCY (MHz)
–50°C
2.0
Switching Frequency
SHDN Pin Bias Current
CURRENT LIMIT (mA)
2.2
250
200
150
100
50
0
50
0
TEMPERATURE (°C)
1937 G04
100
1937 G05
0
20
40
60
DUTY CYCLE (%)
80
100
1937 G06
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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 1.5V or 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. Calculate 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
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BLOCK DIAGRA
VIN
(PIN 6 FOR
SC70 PACKAGE) 5
FB
3
1 SW
–
VREF
1.25V
95mV
–
A1
+
COMPARATOR
DRIVER
RC
+
A2
R
S
Q1
Q
CC
+
Σ
0.2Ω
–
RAMP
GENERATOR
SHDN
4
(PINS 2 AND 5 FOR
SC70 PACKAGE)
SHUTDOWN
2 GND
1937 BD1
1.2MHz
OSCILLATOR
Figure 2. LT1937 Block Diagram
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OPERATIO
The LT1937 uses a constant frequency, current mode
control scheme to provide excellent line and load regulation. 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
voltage exceeds the level at the negative input of A2, the SR
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.
Minimum Output Current
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
pulses. This will result in some low frequency ripple,
although the LED current remains regulated on an average
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
ringing is not harmful; far less spectral energy is contained
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.
VSW
5V/DIV
IL2
50mA/DIV
VOUT
100mV/DIV
0.2µs/DIV
1937 F03
Figure 3. Switching Waveforms at ILED = 4mA, VIN = 3.6V
1937f
4
LT1937
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APPLICATIO S I FOR ATIO
Inductor Selection
Capacitor Selection
A 22µH inductor is recommended for most LT1937 applications. 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.
The small size of ceramic capacitors makes them ideal for
LT1937 applications. X5R and X7R types are recommended 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.
Table 1. Recommended Inductors
MANUFACTURER
PART NUMBER
DCR
(Ω)
CURRENT
RATING
(mA)
LQH3C220
0.71
250
Murata
814-237-1431
www.murata.com
ELJPC220KF
4.0
160
Panasonic
714-373-7334
www.panasonic.com
Taiyo Yuden
MANUFACTURER
PHONE
408-573-4150
URL
www.t-yuden.com
AVX
843-448-9411
www.avxcorp.com
Murata
814-237-1431
www.murata.com
Kemet
408-986-0424
www.kemet.com
Diode Selection
80
Schottky diodes, with their low forward voltage drop and
fast reverse recovery, are the ideal choices for LT1937
applications. The forward voltage drop of a Schottky diode
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 switching frequency of the LT1937. A Schottky diode rated at
100mA to 200mA is sufficient for most LT1937 applications. Some recommended Schottky diodes are listed in
Table 3.
75
Table 3. Recommended Schottky Diodes
CDRH3D16-220
0.53
350
Sumida
847-956-0666
www.Sumida.com
LB2012B220M
1.7
75
Taiyo Yuden
408-573-4150
www.t-yuden.com
LEM2520-220
5.5
125
Taiyo Yuden
408-573-4150
www.t-yuden.com
90
VIN = 3.6V
85 3LEDs
EFFICIENCY (%)
Table 2. Recommended Ceramic Capacitor Manufacturers
70
65
MURATA LQH3C-220
PANASONIC ELJPC220KF
SUMIDA CDRH3D16-220
TAIYO YUDEN LB2012B220M
TAIYO YUDEN LEM2520-220
60
55
50
0
2
4
6 8 10 12 14 16 18 20
LOAD CURRENT (mA)
1937 F04
Figure 4. Efficiency Comparison of Different Inductors
FORWARD VOLTAGE
DIODE
CURRENT DROP CAPACITANCE
(mA)
(V)
(pF)
MANUFACTURER
100
0.58 at
7.0 at
Central
100mA
10V
631-435-1110
www.centralsemi.com
CMDSH2-3
200
0.49 at
15 at
Central
200mA
10V
631-435-1110
www.centralsemi.com
BAT54
200
0.53 at
10 at
Zetex
100mA
25V
631-543-7100
www.zetex.com
PART
NUMBER
CMDSH-3
1937f
5
LT1937
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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
current is 95mV/R1. In order to have accurate LED current,
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:
R1 = 95mV/ILED
(1)
Table 4. R1 Resistor Value Selection
ILED (mA)
R1 (Ω)
5
19.1
10
9.53
12
7.87
15
6.34
20
4.75
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 full current. The typical frequency range of
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.
Open-Circuit Protection
LT1937
In the cases of output open circuit, when the LEDs are
disconnected from the circuit or the LEDs fail, the feedback 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. The current rating of the zener should be larger than
0.1mA.
SHDN
PWM
FB
100mV/DIV
SHDN
2V/DIV
200µs/DIV
1937 F06a
(6a) 1kHz
L
22µH
D
VIN
CIN
1µF
COUT
0.22µF
VIN
FB
100mV/DIV
SW
R2
1k
LT1937
SHDN
GND
SHDN
2V/DIV
FB
R1
6.34Ω
1937 F05
20µs/DIV
1937 F06b
(6b) 10kHz
Figure 5. LED Driver with Open-Circuit Protection
Figure 6. PWM Dimming Control Using the SHDN Pin
1937f
6
LT1937
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APPLICATIO S I FOR ATIO
2. Using a DC Voltage
4. Using a Logic Signal
For some applications, the preferred method of brightness
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
pin bias current. For VDC range from 0V to 2V, the selection
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.
3. Using a Filtered PWM Signal
The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable DC
voltage source in dimming control. The circuit is shown in
Figure 8.
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
an external soft-start circuit, inrush current is about 200mA
as shown in Figure␣ 10. If soft-start is desired, the recommended circuit and the waveforms are shown in Figure 11.
If both soft-start and dimming are used, a 10kHz PWM
signal on SHDN is not recommended. Use a lower frequency or implement dimming through the FB pin as
shown in Figures 7, 8 or 9.
LT1937
LT1937
FB
FB
R3
90k
R2
5k
RINC
VDC
LOGIC
SIGNAL
R1
6.3Ω
2N7002
1937 F09
1937 F07
Figure 7. Dimming Control Using a DC Voltage
R1
Figure 9. Dimming Control Using a Logic Signal
IIN
100mA/DIV
LT1937
FB
10k
R3
90k
FB
100mV/DIV
R2
5k
PWM
0.1µF
R1
6.3Ω
1937 F08
Figure 8. Dimming Control Using a Filtered PWM Signal
SHDN
2V/DIV
VIN = 3.6V
THREE LEDs
15mA
50µs/DIV
1937 F09
Figure 10. Start-Up Waveforms Without Soft-Startup Circuit
1937f
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LT1937
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APPLICATIO S I FOR ATIO
D1
IIN
100mA/DIV
2.2nF
LT1937
FB
FB
100mV/DIV
R2
1k
D2
COUT
SHDN
2V/DIV
R1
6.34Ω
5k
VIN = 3.6V
THREE LEDs
15mA
D2: MMBT
1937 F11a
(11a) Recommended Soft-Startup Circuit
50µs/DIV
1937 F11b
(11b) Soft-Startup Waveforms
Figure 11. Recommended Soft-Startup Circuit and Waveforms
Board Layout Consideration
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To maximize efficiency, switch rise and fall times are made
as short as possible. To prevent electromagnetic interference (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
VIN
D
CO
area of all traces connected to the SW pin and always use
a ground plane under the switching regulator to minimize
interplane coupling. In addition, the ground connection for
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.
1
5
CO
CIN
2
GND
4
3
SHDN
R2
6
2
5
3
4
CIN
GND
SHDN
R1
1937 F12a
R3
1
R2
R1
DIMMING
CONTROL
VIN
D
DIMMING
CONTROL
1937 F12b
R3
(SOT-23 Package)
(SC70 Package)
Figure 12. Recommended Component Placement
1937f
8
LT1937
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TYPICAL APPLICATIO S
Li-Ion to Two White LEDs
L
22µH
86
D
VIN = 3.6V
84
CIN
1µF
COUT
1µF
VDC
DIMMING
VIN
SW
90k
LT1937
SHDN
82
EFFICIENCY (%)
VIN
3V TO 5V
Two LED Efficiency
5k
VIN = 3V
80
78
76
FB
74
R1
2Ω
GND
CIN: TAIYO YUDEN JMK107BJ105
COUT: AVX 0603ZD105
D: CENTRAL CMDSH2-3
L: MURATA LQH3C220
72
70
1937 TA05a
0
10
20
30
40
LED CURRENT (mA)
1937 TA05a
Li-Ion to Three White LEDs
90
D
CIN
1µF
VDC
DIMMING
VIN
SW
90k
LT1937
SHDN
5k
FB
GND
CIN: TAIYO YUDEN JMK107BJ105
COUT: AVX 0603YD224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
85
COUT
0.22µF
EFFICIENCY (%)
VIN
3V TO 5V
L
22µH
Three LED Efficiency
R1
4Ω
80
VIN = 3V
VIN = 3.6V
75
70
65
1937 TA01a
60
0
5
10
15
LED CURRENT (mA)
20
1937 TA01b
1937f
9
LT1937
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TYPICAL APPLICATIO S
Li-Ion to Five White LEDs
85
L
22µH
D
CIN
1µF
COUT
0.22µF
VDC
DIMMING
VIN
SW
90k
LT1937
SHDN
80
EFFICIENCY (%)
VIN
3V TO 5V
Five LED Efficiency
5k
FB
VIN = 3V
75
VIN = 3.6V
70
R1
4Ω
GND
CIN: TAIYO YUDEN JMK107BJ105
COUT: TAIYO YUDEN GMK212BJ224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
65
1937 TA03a
0
12
Seven LED Efficiency
D
COUT
0.22µF
VDC
DIMMING
SW
90k
LT1937
5k
FB
GND
CIN: TAIYO YUDEN JMK107BJ105
COUT: TAIYO YUDEN GMK212BJ224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
80
EFFICIENCY (%)
CIN
1µF
SHDN
10
85
L
22µH
VIN
4
6
8
LOAD CURRENT (mA)
1937 TA03b
5V to Seven White LEDs
VIN
5V
2
75
70
R1
4Ω
1937 TA04a
65
0
5
10
LOAD CURRENT (mA)
15
1937 TA04b
1937f
10
LT1937
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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
2.80 BSC
1.4 MIN
3.85 MAX 2.62 REF
1.50 – 1.75
(NOTE 4)
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
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
NOTE:
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
1.90 BSC
S5 TSOT-23 0302
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
0.96 MIN
3.26 MAX 2.1 REF
INDEX AREA
(NOTE 6)
1.80 – 2.40 1.15 – 1.35
(NOTE 4)
PIN 1
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.65 BSC
0.15 – 0.30
6 PLCS (NOTE 3)
0.10 – 0.40
0.80 – 1.00
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
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
0.00 – 0.10
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
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LT1937
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TYPICAL APPLICATIO
Li-Ion to Four White LEDs
L
22µH
VIN
3V TO 5V
D
CIN
1µF
COUT
0.22µF
VDC
DIMMING
VIN
SW
90k
LT1937
SHDN
5k
FB
R1
4Ω
GND
CIN: TAIYO YUDEN JMK107BJ105
COUT: AVX 0603YD224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
1937 TA02a
Four LED Efficiency
85
Switching Waveforms
VSW
10V/DIV
EFFICIENCY (%)
80
VIN = 3V
VIN = 3.6V
ISW
100mA/DIV
75
VOUT
100mV/DIV
70
60
0
15
5
10
LOAD CURRENT (mA)
20
VIN = 3.6V
FOUR LEDs
15mA
1937 TA02c
0.2µs/DIV
1937 TA02b
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1937f
12
Linear Technology Corporation
LT/TP 0702 2K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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 LINEAR TECHNOLOGY CORPORATION 2002