LT3757 datasheet(21/38 Pages) AD

21 / 38 page

LTC7840

Rev 0

For more information www.analog.com

between the SS pin and SGND is discharged by a 1.25µA

current. When the voltage on SS pin reaches 0V, the ITH

pin is released and the controller retries to soft-start, as

described in the Shutdown and Start-Up section. The

hiccup mode is disabled during the soft-start period. To

realize the function of the hiccup mode, a minimum 0.1µF

soft-start capacitor has to be connected between the SS

pin and SGND. The sleep time can be estimated by:

1.5V

1.25µA

tSLEEP = CSS •

= 1.2 • CSS

Compared with the start-up time estimated in the

Shutdown and Start-Up section, the sleep time is roughly

10 times the start-up time.

If the overcurrent situation is removed continuously for

two or more switching periods before the 16 switching

period timer expires, the 16 switching period timer will

reset to zero and the output will soft recover by using the

internal soft-start, thus reducing output overshoot. In the

absence of this feature, the output capacitors would have

been charged at current limit, and in applications with

minimal output capacitance, this may have resulted in

output overshoot.

Figure 12.

2s/DIV

5V/DIV

VOUT

50V/DIV

GATE

10V/DIV

ITH

2V/DIV

7840 F12

Hiccup Mode Overcurrent Protection and Recovery

OPERATION

LT3757 Datasheet(PDF) 21 Page - Analog Devices