Diodes AP3608E Manuel d'utilisateur télécharger pdf (Page 10)

EIGHT-CHANNEL CONSTANT CURRENT SINK WITH CURRENT MATCH AP3608E

Data Sheet

Mar. 2011 Rev. 1. 5 BCD Semiconductor Manufacturing Limited

Function Description (Continued)

3. Open LED Self-Check and Protection

The AP3608E can work with a DC/DC converter to

achieve good performance, such as self-check and

protection against open LED. The SDB pin and FB pin

are the interface terminals for working with the DC/

DC converter. FB pin samples voltage of each

channel, and outputs the lowest voltage of all strings to

DC/DC converter. When AP3608E gets shutdown

signal from EN pin or all channels are inactive, SDB

pin outputs low logic to DC/DC converter. When

AP3608E is on PWM dimming mode, the SDB pin

outputs the signal which is synchronous with PWM

signal to DC/DC converter. Figure 11 is the typical cir-

cuit of AP3608E applied with a boost converter

AP3039.

If any enabled LED string opens, voltage on the

corresponding CHX pin goes to zero and the FB pin

outputs the zero voltage to boost converter. So the

boost converter operates in open loop and the voltage

on remaining CHX pin goes higher. Once the voltage

on remaining CHX pin reaches the self-check voltage

3V, the AP3608E begins looking up the open string.

After finding the open channel, AP3608E removes the

corresponding CHX pin from boost control loop, then

the boost circuit is controlled in the normal manner.

Once the circuit returns normal operation, the voltage

on the CHX pin is regulated to the normal level. It is

necessary to pay attention that the open strings are

removed from boost regulation, but not disabled. If the

open LED string is reconnected, it will sink current up

to the programmed current level.

4. Parallel Operation Mode

The AP3608E can be paralleled to drive more strings

of LED. Connecting an AP3608E SDB pin and FB pin

with another AP3608E SDBX pin and FBX pin can

achieve parallel application. More details please refer

to Figure 11.

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Diodes AP3608E Manuel d'utilisateur Page 10