LTC3218
DESCRIPTION
1
WARNING!
Do not look directly at operating LED.
This circuit produces light that can damage eyes.
Demonstration circuit 1030 is a 400mA Single Wire
Camera LED Charge Pump featuring the LTC3218. This
circuit will provide 50mA of continuous torch current or
a flash current at 300mA or 400mA. The LTC3218 has a
built-in 2-second flash timer to protect the LED in case of
faults during flash mode.
The LTC3218 is a low-noise, high current charge pump
capable of flashing a Camera LED up to 400mA. The
LTC3218 design requires only three capacitors and one
program resistor to provide a complete Camera Driver
circuit with one torch and two flash current settings. A
second programming resistor may be used to provide a
wider range of LED torch and flash current settings.
Pressing the ENT push button, SW1, enables torch
mode. Pressing the ENF push button, SW2, enables flash
mode. Pressing both ENT and ENF push buttons enables
the high intensity flash mode. Pulse generator(s) may be
connected to the ENF and/or ENT terminals to better con-
trol the pulse timing for evaluation of flash and current
performance.
Built-in soft-start circuit prevents excessive inrush cur-
rents during start up. The LED output current is regulated
using an internal high side resistor allowing the LED
cathode to be connected directly to ground. The Charge
Pump Output (CPO) voltage is monitored and automati-
cally switches to 2X mode only when a dropout has been
detected to optimize efficiency. Refer to the LTC3218
datasheet for more information on this device.
Design files for this circuit board are available. Call
the LTC factory.
L
, LTC, LTM, LT, are registered trademarks of Linear Technology Corporation. Other prod-
uct names may be trademarks of the companies that manufacture the products.
PERFORMANCE SUMMARY
Specifications are at T
A
= 25°C
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
Input Supply Range
2.9 4.5
V
I
VIN
Shutdown Current
ENF = ENT = LOW, V
CPO
= 0V
1.1
3
µA
I
VIN
Operating Current
ICPO
= 0mA, 1X Mode
ICPO
= 0mA, 2X Mode
980
6.7
µA
mA
I
LED
Torch Current
ENT = HIGH, ENF = LOW
45
mA
I
LED
Flash Current
ENT = LOW, ENF = HIGH
290
mA
I
LED
High Flash Current
ENT = HIGH, ENF = HIGH
390
mA
I
LED
Dropout Voltage (V
ILED
)
Mode Switching Threshold, V
CPO
– V
ILED
,
I
LED
= 100mA
7
mV
Minimum LED Forward Voltage
I
LED
= 50mA
2.2
V
Charge Pump Output Clamp Voltage
5.3
V
DEMO CIRCUIT 1030
QUICK START GUIDE
LTC3218
400mA Single Wire Camera
LED Charge Pump
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