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t3 =

CSS x 4V

55 PA

= 73 k: x CSS

t2 =

CSS x 1V

1 PA

= 1 M: x CSS

t1 =

CRES x 2.5V

22 PA

= 114 k: x CRES

RES

Current Limit Detected

at CS

2.5V

+55 2A

+1 2A

LM5035

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SNVS428H – JANUARY 2006 – REVISED OCTOBER 2015

8.2.2.8 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 shown in Figure 25.

Figure 26. Hiccup Overload Restart Timing

In the case of continuous cycle-by-cycle current-limit detection at the CS pin, refer to Figure 26 and use

Equation 17 to calculate the time required for CRES to reach the 2.5-V hiccup mode threshold.

(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. Use

Equation 18 to calculate the value of t2.

(18)

If CSS = 0.01 µF, the value of t2 is ≊ 10 ms.

The soft-start time t3 is set by the internal 55-µA current source. Use Equation 19 to calculate the value of t3.

(19)

If CSS = 0.01 µF, the value of t3 is ≊ 730 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. It is recommended 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 must be connected to ground (AGND).

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