CAT3626_08 Datasheet, PDF (9/15 Pages) Catalyst Semiconductor – 6-Channel LED Driver with I2C™ Interface

CAT3626
BLOCK DIAGRAM
1µF
C_1-
C₁₊
1µF
C_2- C₂₊
V_IN
C_IN
1µF
EN
SDA
SCL
1x mode (LDO)
1.5x Charge Pump
V_OUT
1MHz
Oscillator
Mode Control
Reference
Voltage
Current
Setting DAC
Serial
Interface
Registers
GND
LEDA1
LEDA2
LEDB1
LEDB2
LEDC1
LEDC2
6 Current
Sink Regulators
Figure 2. CAT3626 Functional Block Diagram
C_OUT
1µF
BASIC OPERATION
At power-up, the CAT3626 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 LEDs
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 (after a fixed time of
400µs) into 1.5x mode.
In 1.5x mode, the output is approximately equal to 1.5
times the input supply voltage (less any internal
voltage losses).
The above sequence is repeated each and every time
the chip is either powered-up or taken out of shutdown
(via EN pin), or the RegEn register is accessed by
write cycle.
LED CURRENT SETTING
The LED current setting is programmed via the I²C
serial interface and is stored in four
8-bit registers RegA, RegB, RegC and RegEn as
follows:
ƒ RegA stores the LED current for group A
(LEDA1 and LEDA2 channels),
ƒ RegB stores the LED current for group B
(LEDB1 and LEDB2 channels),
ƒ RegC stores the LED current for group C
(LEDC1 and LEDC2 channels),
ƒ RegEn selects the on/off state of each of the 6
LED channels.
At each write access to RegEn, the driver automatically
reconfigures to the mode (1x or 1.5x) that provides the
highest efficiency.
© Catalyst Semiconductor, Inc.
9
Characteristics subject to change without notice
Doc. No. MD-5014 Rev. D