CAT3626 datasheet(9/15 Pages) CATALYST

9 / 15 page

CAT3626

Doc. No. MD-5014 Rev. D

Characteristics subject to change without notice

BLOCK DIAGRAM

Figure 2. CAT3626 Functional 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.

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:

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.

At each write access to RegEn, the driver automatically

reconfigures to the mode (1x or 1.5x) that provides the

highest efficiency.

Mode Control

1MHz

Oscillator

Current

Setting DAC

Serial

Interface

Registers

Reference

Voltage

1x mode (LDO)

1.5x Charge Pump

VIN

C1-

C2-

C1+

C2+

VOUT

COUT

CIN

1µF

LEDA1

LEDA2

LEDB1

LEDB2

LEDC1

LEDC2

GND

6 Current

Sink Regulators

SDA

SCL

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