cat3626 Catalyst Semiconductor, cat3626 Datasheet - Page 9

• Manufacturer Part Number: cat3626
• Description: 6-channel Led Driver With I?c Interface
• Manufacturer: Catalyst Semiconductor

BLOCK DIAGRAM
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.
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
V
IN
SDA
SCL
EN
1µF
C
IN
Interface
Serial
C
Setting DAC
1-
Reference
Registers
Oscillator
Current
Voltage
1µF
1MHz
Figure 2. CAT3626 Functional Block Diagram
1.5x Charge Pump
1x mode (LDO)
C
1+
C
2-
Mode Control
1µF
C
2+
9
LED CURRENT SETTING
The LED current setting is programmed via the I
serial interface and is stored in four
8-bit registers RegA, RegB, RegC and RegEn as
follows:
At each write access to RegEn, the driver automatically
reconfigures to the mode (1x or 1.5x) that provides the
highest efficiency.
GND
RegA stores the LED current for group A
(LEDA1 and LEDA2 channels),
RegB stores the LED current for group B
(LEDB1 and LEDB2 channels),
RegC stores the LED current for group C
(LEDC1 and LEDC2 channels),
RegEn selects the on/off state of each of the 6
LED channels.
6 Current
Sink Regulators
V
LEDA1
LEDA2
LEDB1
LEDB2
LEDC1
LEDC2
OUT
Doc. No. MD-5014 Rev. C
CAT3626
C
1µF
OUT
2
C