Datasheet

CAT3637
http://onsemi.com
10
Simplified Block Diagram
Mode Control
0.8, 1.1 MHz
Oscillator
Current
Setting DAC
Serial
Interface
Registers
Reference
Voltage
1x mode (LDO)
1.33x, 1.5x, 2x Charge Pump
EN/SET
LED1
LED2
LED3
LED4
LED5
LED6
100 kΩ
GND
6 Current
Regulators
Figure 23. CAT3637 Functional Block Diagram
V
OUT
V
IN
C
2+
C
2−
C
1−
C
1+
Basic Operation
At power−up, the CAT3637 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 output voltage is insufficient or falls to a level where
the regulated current cannot be maintained, the device
automatically switches into 1.33x mode (after a fixed delay
time of about 120 ms). In 1.33x mode, the output voltage is
approximately equal to 1.33 times the input supply voltage
(less any internal voltage losses).
If the output voltage is still insufficient or falls to a level
where the regulated currents cannot be maintained, the
device will automatically switch to the 1.5x mode (after a
fixed delay time of about 400 ms). In 1.5x mode, the output
is approximately equal to 1.5 times the input supply voltage
(less any internal voltage losses).
If the output voltage is still insufficient to drive the LEDs,
it will automatically switch into 2x mode where the output
is approximately equal to 2 times the input supply voltage
(less any internal voltage losses).
If the device detects a sufficient output voltage to drive all
LED currents in 1x mode, it will revert back to 1x mode. This
only applies for changing back to the 1x mode.