RES

SS

LO

HO

5V

t1

Current Limit Detected

at CS

2.5V

0V

+110 PA

+1 PA

t2

t3

#1V

t3 =

CSS x 4V

110 PA

= 40 k: x CSS

t2 =

CSS x 1V

1 PA

= 1 M: x CSS

t1 =

CRES x 2.5V

22 PA

= 114 k: x CRES

30

LM5035C

SNVS631D – JANUARY 2010 – REVISED OCTOBER 2016

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Copyright © 2010–2016, Texas Instruments Incorporated

9.2.2.8 Hiccup Mode Current Limit Restart (RES)

The basic operation of the hiccup mode current limit restart is described in the functional description. The delay

time to restart is programmed with the selection of the RES pin capacitor CRES as illustrated in Figure 25.

In the case of continuous cycle-by-cycle current limit detection at the CS pin, the time required for CRES to reach

the 2.5-V hiccup mode threshold is:

(17)

For example, if CRES = 0.01 µF the time t1 is approximately 1.14 ms.

The cool down time, t2 is set by the soft-start capacitor (CSS) and the internal 1-µA SS current source, and is

equal to Equation 18:

(18)

If CSS = 0.01 µF t2 is ≊10 ms.

The soft-start time t3 is set by the internal 110-µA current source, and is equal to Equation 19.

(19)

If CSS = 0.01 µF t3 is ≊363 µs.

The time t2 provides a periodic cool-down time for the power converter in the event of a sustained overload or

short circuit. This off time results in lower average input current and lower power dissipation within the power

components. TI recommends that the ratio of t2 / (t1 + t3) be in the range of 5 to 10 to take advantage of this

feature.

If the application requires no delay from the first detection of a current limit condition to the onset of the hiccup

mode (t1 = 0), the RES pin can be left open (no external capacitor). If it is desired to disable the hiccup mode

entirely, the RES pin should be connected to ground (AGND).

Figure 26. Hiccup Overload Restart Timing