CLK

Q

S

R

Drivers Off

SS

PWM

COMP

CS

RES

LM5035B

SS

Drivers Off

Voltage

Feedback

Current

Sense

Circuit

CRES

Restart

Comparator

Restart

Latch

2.5V

5V

Restart

Current

Source

Logic

SS

Logic

To Output

Drivers

Current

Limit

0.25V

CSS

Soft-start

100 mV

110 PA

110 PA

1 PA

22 PA

12 PA

LM5035B

www.ti.com

SNVS613C – JULY 2009 – REVISED APRIL 2013

•

If the overload condition persists after restart, cycle-by-cycle current limiting will begin to increase the voltage

on the RES capacitor again, repeating the hiccup mode sequence

•

If the overload condition no longer exists after restart, the RES pin will be held at ground by the 12 µA current

sink and normal operation resumes

The overload timer function is very versatile and can be configured for the following modes of protection:

1. Cycle-by-cycle only: The hiccup mode can be completely disabled by connecting a zero to 50 k

Ω resistor

from the RES pin to AGND. In this configuration, the cycle-by-cycle protection will limit the output current

indefinitely and no hiccup sequences will occur.

2. Hiccup only: The timer can be configured for immediate activation of a hiccup sequence upon detection of

an overload by leaving the RES pin open circuit.

3. Delayed Hiccup: Connecting a capacitor to the RES pin provides a programmed interval of cycle-by-cycle

limiting before initiating a hiccup mode restart, as previously described. The dual advantages of this

configuration are that a short term overload will not cause a hiccup mode restart but during extended

overload conditions, the average dissipation of the power converter will be very low.

4. Externally Controlled Hiccup: The RES pin can also be used as an input. By externally driving the pin to a

level greater than the 2.5V hiccup threshold, the controller will be forced into the delayed restart sequence.

For example, the external trigger for a delayed restart sequence could come from an over-temperature

protection circuit or an output over-voltage sensor.

Figure 14. Current Limit Restart Circuit

Copyright © 2009–2013, Texas Instruments Incorporated

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