CAT3644 Datasheet, PDF (9/14 Pages) Catalyst Semiconductor – 4-Channel Ultra High Efficiency Quad-Mode TM LED Driver

BLOCK DIAGRAM
V_IN
C_1-
C₁₊
C_2- C₂₊
1x mode (LDO)
4/3x, 3/2x, 2x Charge Pump
V_OUT
EN/DIM
100kΩ
Serial
Interface
1, 1.3MHz
Oscillator
Referece
Voltage
Registers
Current
Setting DAC
Mode Control
RSET
GND
LED1
LED2
LED3
LED4
LED Channel
Current Regulators
CAT3644
Figure 2. CAT3644 Functional Block Diagram
BASIC OPERATION
At power-up, the CAT3644 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 400μs). In 1.33x
mode, the output voltage is approximately equal to
1.33 times the input supply voltage (less any internal
voltage losses).
This 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 500mV.
© 2007 Catalyst Semiconductor, Inc.
9
Characteristics subject to change without notice
Doc. No. 5023, Rev. B