LM5045MHXSLASHNOPB.A datasheet(30/47 Pages) TI2

30 / 47 page

Hiccup Mode off-time

Soft-Start

Restart delay

Count to Eight

THICCUP =

5 µA

CRES x (2.0Vx8)

10 µA

CRES x ((2.0Vx8) + 1.0V)

TCS =

CRES x 1.0V

30 2A

LM5045

RCS

VIN

AGND

LM5045

SNVS699H – FEBRUARY 2011 – REVISED JANUARY 2015

www.ti.com

Figure 28. Resistor Current Sense

8.2.2.5 Hiccup Mode Current Limit Restart

The operation of the hiccup mode restart circuit is explained in the section. During a continuous current limit

condition, the RES pin is charged with 30 µA current source. The restart delay time required to reach the 1.0 V

threshold is given by:

(8)

This establishes the time allowed before the IC initiates a hiccup restart sequence. For example, if the CRES =

0.01 µF, the time TCS as noted in Figure 29 below is 334 µs. Once the RES pin reaches 1.0 V, the 30 µA

current source is turned-off and a 10 µA current source is turned-on during the ramp up to 4 V and a 5 µA is

turned on during the ramp down to 2 V. The hiccup mode off-time is given by:

(9)

With a CRES = 0.01 µF, the hiccup time is 49 ms. Once the hiccup time is finished, the RES pin is pulled low and

the SS pin is released allowing a soft-start sequence to commence. Once the SS pin reaches 1 V, the PWM

pulses will commence. The hiccup mode provides a cool-down period for the power converter in the event of a

sustained overload condition thereby lowering the average input current and temperature of the power

components during such an event.

Figure 29. Hiccup Mode Delay and Soft-Start Timing Diagram

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LM5045MHX/NOPB.A Datasheet(PDF) 30 Page - Texas Instruments