CAT3637HV3-GT2 Datasheet, PDF (9/14 Pages) ON Semiconductor – 6-Channel Programmable High Efficiency Quad-Mode LED Driver

SIMPLIFIED BLOCK DIAGRAM
C_1-
C₁₊
C_2- C₂₊
V_IN
1x mode (LDO)
1.33x, 1.5x, 2x Charge Pump
V_OUT
CAT3637
EN/SET
0.8, 1.1MHz
Oscillator
100kΩ
Serial
Interface
Reference
Voltage
Registers
Current
Setting DAC
Mode Control
LED1
LED2
LED3
LED4
LED5
LED6
6 Current
Regulators
GND
Figure 2. CAT3637 Functional Block Diagram
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 120μs). 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 400μs). 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.
© 2008 SCILLC. All rights reserved.
9
Characteristics subject to change without notice
Doc. No. MD-5033 Rev. C