LTC3216 Datasheet, PDF (7/12 Pages) Linear Technology – 1A Low Noise High Current LED Charge Pump with Independent Torch/Flash Current Control

U
OPERATIO
R_OL
+
1.5V_IN
OR
2V_IN
–+
CPO
–
LTC3216
to 500mA continuously, and up to 1A for pulsed operation
with a 10% duty cycle. Pulsed operation may be achieved
by toggling the EN1 and EN2 bits. In either continuous or
pulsed operation, proper board layout is required for
effective heat sinking.
Figure 1. Charge Pump Open-Loop Thevenin-Equivalent Circuit
R_OL is dependent on a number of factors including
the oscillator frequency, flying capacitor values and
switch resistances.
From Figure 1, we can see that the output current is
proportional to:
(1.5V_IN – CPO)/R_OL or (2V_IN – CPO)/R_OL
(2)
in the 1.5x mode or 2x mode respectively.
Current Levels
The LTC3216 may be programmed to have three discrete
current levels. These are the LOW, HIGH and LOW + HIGH
current levels. The LOW and HIGH currents are set by the
resistors connected between I_SET1 and I_SET2 pins, respec-
tively, to GND. The LOW + HIGH current mode supplies a
current that is equal to sum of the LOW and HIGH currents.
Due to the low output impedance of this part, care should
be taken in selecting current levels. This part can supply up
Mode Switching
The LTC3216 will automatically switch from 1x mode to
1.5x mode, and subsequently from 1.5x mode to 2x mode
whenever a dropout condition is detected at the I_LED pin.
In the LOW current mode, the part will wait approximately
150ms after dropout is detected before switching to the
next mode. In the HIGH and LOW + HIGH current modes,
the part will wait approximately 2ms before switching to
the next mode. These delays allow the LED to warm up and
reduce its forward voltage which may remove the dropout
condition.
In order to reset the part back into 1x mode, the LTC3216
must be brought into shutdown (EN1 = EN2 = LOW).
Immediately after the part has been brought to shutdown,
it may be set to the desired output current level via the EN1
and EN2 pins. An internal comparator will not allow the
main switches to connect V_IN and CPO in 1x mode until the
voltage at the CPO pin has decayed to less than or equal to
the voltage at the V_IN pin.
3216fa
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