CS5161, CS5161H

http://onsemi.com

11

latch. This causes the top MOSFET to shut off,

disconnecting the regulator from it’s input voltage. The Soft

Start capacitor is then slowly discharged by a 2.0 μA current

source until it reaches it’s lower 0.7 V threshold. The

regulator will then attempt to restart normally, operating in

it’s extended off time mode with a 50% duty cycle, while the

Soft Start capacitor is charged with a 60 μA charge current.

If the short circuit condition persists, the regulator output

before the Soft Start capacitor is charged to it’s upper 2.5 V

threshold. If this happens the cycle will repeat itself until the

short is removed. The Soft Start charge/discharge current

ratio

sets

the

duty

cycle

for

the

pulses

(2.0 μA/60 μA = 3.3%), while actual duty cycle is half that

due to the extended off time mode (1.65%).

This protection feature results in less stress to the

regulator components, input power supply, and PC board

traces than occurs with constant current limit protection (see

Figures 12 and 13).

If the short circuit condition is removed, output voltage

will rise above the 1.0 V level, preventing the FAULT latch

from being set, allowing normal operation to resume.

Figure 12. CS5161/5161H Hiccup Mode Short Circuit

Protection. Gate Pulses are Delivered While the Soft

Start Capacitor Charges, and Cease During Discharge

M 25.0 ms

Trace 3− Soft Start Timing Capacitor (1.0 V/div.)

Trace 4− 5.0 V Supply Voltage (2.0 V/div.)

Trace 2− Inductor Switching Node (2.0 V/div.)

Figure 13. CS5161/5161H Startup with Regulator

Output Shorted

M 50.0 μs

Trace 4− 5.0 V from PC Power Supply (2.0 V/div.)

Trace 2− Inductor Switching Node (2.0 V/div.)

Overvoltage Protection

Overvoltage protection (OVP) is provided as result of the

additional external components. The control loop responds

to an overvoltage condition within 100 ns, causing the top

MOSFET to shut off, disconnecting the regulator from it’s

input voltage. The bottom MOSFET is then activated,

resulting in a “crowbar” action to clamp the output voltage

and prevent damage to the load (see Figures 14 and 15). The

regulator will remain in this state until the overvoltage

condition ceases or the input voltage is pulled low. The

bottom FET and board trace must be properly designed to

implement the OVP function.

Figure 14. CS5161/5161H OVP Response to an

Input−to−Output Short Circuit by Immediately

Providing 0% Duty Cycle, Crow−Barring the Input

Voltage to Ground

M 10.0 μs

Trace 1− Regulator Output Voltage (1.0 V/div.)

Trace 2− Inductor Switching Node 5.0 V/div.)

Trace 4− 5.0 V from PC Power Supply (5.0 V/div.)