LM5032 datasheet(13/22 Pages) NSC

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Hiccup Mode Current Limit Restart

(Continued)

The 10 µA discharge current source at RES is enabled

pulling the RES pin to ground.

b) Current limit repeatedly detected at both CS inputs:

The 20 µA current source at RES is enabled continuously to

charge the RES pin capacitor as shown in Figure 18. The

current limit comparators also terminate the PWM output

pulses to provide a cycle-by-cycle current limiting. When the

voltage on the RES capacitor reaches the 2.55V restart

comparator threshold, the comparator sets the Restart Latch

which produces the following restart sequence:

•

The SS1 and SS2 pin charging currents are reduced from

50µA to 1 µA.

•

An internal MOSFET is turned on to discharge the RES

pin capacitor.

•

The internal MOSFETs at SS1 and SS2 are turned on to

discharge the Soft-start capacitors.

•

COMP1 and COMP2 follow SS1 and SS2 respectively

and reduce the PWM duty cycles to zero.

•

When the voltages at the SS pins fall below 200mV, the

internal MOSFETs at the SS pins are turned off allowing

the SS pins to be charged by the 1µA current sources.

•

When either SS pin reaches )1.5V its PWM controller

produces the first pulse of a soft-start sequence which

resets the Restart Latch. The SS charging currents are

increased to 50 µA and the soft-start sequence continues

at the normal rate.

If the overload condition still exists, the voltage at RES

begins to increase again and repeat the restart cycle as

shown in Figure 18. If the overload condition has been

cleared, the RES pin is held at ground by the 10 µA current

source.

c) Current limit repeatedly detected at one of the two CS

inputs:

In this condition the RES pin capacitor is charged by the 20

µA current source once each clock cycle of the current

limited regulator, and discharged by the 10 µA current source

once each clock cycle of the unaffected regulator. The volt-

age at the RES pin increases one fourth as fast as in case b)

described above. The current limited regulator operates in a

cycle-by-cycle current limit mode until the voltage at RES

reaches the 2.55V threshold. When the Restart Comparator

output switches high the Restart Latch is set, both SS pin

capacitors are discharged to disable the regulator channels,

and a restart sequence begins as described in case b)

above.

To determine the value of the RES pin capacitor, see the

Applications Information section.

20135023

FIGURE 17. Current Limit Restart Circuit

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