CAT3604V

http://onsemi.com

10

Block Diagram

Figure 25. CAT3604V Functional Block Diagram

Mode Control

1, 1.3 MHz

Oscillator

Current

Setting

Reference

Voltage

1x mode (LDO)

1.33x, 1.5x, 2x Charge Pump

VIN

VOUT

EN

RSET

GND

LED1

LED2

LED3

LED4

LED Channel

Current Regulators

Basic Operation

At power−up, the CAT3604V 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 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 400

ms). In 1.33x mode, the output voltage is

approximately equal to 1.33 times the input supply voltage

(less any internal voltage losses).

This 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

is about 500 mV

LED Current Selection

The LED current is set to by the external resistor RSET as

follows:

LED current + 132

0.6 V

The EN pin enables and disables the device. The LED

driver enters a “zero current” shutdown mode if EN is held

low for 1.5 ms or more.

As soon as the EN input goes low, all LED channels are

instantly disabled, where the LED current is set to zero. As

long as the CAT3604V is not in shutdown mode, the LEDs

turn on as soon as the EN goes high.

Unused LED Channels

For applications not requiring all the channels, it is

recommended to connect the unused LED pins directly to

VOUT (see Figure 26).

Figure 26. Application with 3 LEDs

GND

LED2

LED3

LED1

LED4

RSET

EN

CAT3604V

VIN

VOUT

1 mF

1 mF

C1−

C1+

C2−

C2+

1 mF

1 mF

ON OFF

Protection Mode

If an LED is disconnected, the device senses that, run the

diagnostics, then ignores that channel and goes back to the

most effective mode. When all LEDs are disconnected, the