CAT3637

© Catalyst Semiconductor, Inc.

9

Doc. No. MD-5033 Rev. A

Characteristics subject to change without notice

SIMPLIFIED BLOCK DIAGRAM

Figure 2. CAT3637 Functional Block Diagram

BASIC OPERATION

At power-up, the CAT3637 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 output voltage is insufficient or falls to a level

where the regulated current cannot be maintained, the

device automatically switches into 1.33x mode (after a

fixed delay time of about 120μs). In 1.33x mode, the

output voltage is approximately equal to 1.33 times the

input supply voltage (less any internal voltage losses).

If the output voltage is still insufficient or falls to a level

where the regulated currents cannot be maintained, the

device will automatically switch to the 1.5x mode (after

a fixed delay time of about 400μs). In 1.5x mode, the

output is approximately equal to 1.5 times the input

supply voltage (less any internal voltage losses).

If the output voltage is still insufficient to drive the

LEDs, it will automatically switch into 2x mode where

the output is approximately equal to 2 times the input

supply voltage (less any internal voltage losses).

If the device detects a sufficient output voltage

to drive all LED currents in 1x mode, it will revert back

to 1x mode. This only applies for changing back to the

1x mode.

Mode Control

0.8, 1.1MHz

Oscillator

Current

Setting DAC

Serial

Interface

Registers

Reference

Voltage

1x mode (LDO)

1.33x, 1.5x, 2x Charge Pump

EN/SET

LED1

LED2

LED3

LED4

LED5

LED6

100kΩ

GND

6 Current

Regulators