CAT3643
BLOCK DIAGRAM
C
C
C
2-
C
2+
1-
1+
V
IN
V
1x mode (LDO)
1.33x, 1.5x, 2x Charge Pump
OUT
Mode Control
1, 1.3MHz
Oscillator
EN/DIM
LED1
LED2
100kꢀ
Serial
Reference
Voltage
Interface
LED3
Current
Setting DAC
LED Channel
Current Regulators
Registers
RSET
GND
Figure 2. 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.
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
(VHYS) and is about 500mV.
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).
Doc. No. MD-5022 Rev. E
10
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CATALYST [ CATALYST SEMICONDUCTOR ]
