CAT3643 Datasheet, PDF (10/15 Pages) Catalyst Semiconductor – 3-Channel Ultra High Efficiency Quad-Mode TM LED Driver

Block Diagram
V_IN
CAT3643
C_1− C₁₊
C_2− C₂₊
1x mode (LDO)
1.33x, 1.5x, 2x Charge Pump
V_OUT
EN/DIM
100 kΩ
Serial
Interface
1, 1.3 MHz
Oscillator
Reference
Voltage
Mode Control
Registers
Current
Setting DAC
LED1
LED2
LED3
LED Channel
Current Regulators
RSET
GND
Figure 28. CAT3643 Functional Block Diagram
Basic Operation
At power−up, the CAT3643 starts operating in 1x mode
where the output will be approximately equal to the input
supply voltage (less any internal voltage losses). If the
output voltage is sufficient to regulate all LED currents, the
device remains in 1x operating mode.
If the input voltage is insufficient or falls to a level where
the regulated currents cannot be maintained, the device
automatically switches into 1.33x mode (after a fixed delay
time of about 400 ms). In 1.33x mode, the output voltage is
approximately equal to 1.33 times the input supply voltage
(less any internal voltage losses).
The above sequence repeats in the 1.33x and 1.5x mode
until the driver enters the 2x mode. In 1.5x mode, the output
voltage is approximately equal to 1.5 times the input supply
voltage. While in 2x mode, the output is approximately
equal to 2 times the input supply voltage.
If the device detects a sufficient input voltage is present to
drive all LED currents in 1x mode, it will change
automatically back to 1x mode. This only applies for
changing back to the 1x mode. The difference between the
input voltage when exiting 1x mode and returning to 1x
mode is called the 1x mode transition hysteresis (V_HYS) and
is about 500 mV.
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