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CS5156GDR16

CPU 5-Bit Nonsynchronous Buck Controller

Cherry semiconductor 

Applications Information: continued

If the short circuit condition is removed, output voltage

will rise above the 1V level, preventing the FAULT latch

from being set, allowing normal operation to resume.

Trace1 - Regulator Output Voltage (1V/div.)

Trace 2 - Inductor Switching Node (5V/div.)

Trace 3 - Output Current (13 to 0.5 Amps) (20V/div.)

Figure 9: CS5156 demonstration board response to 13A load turn off

(output set for 2.8V). V2™ control topology immediately connects

inductor to ground, providing 0% duty cycle. Regulation is achieved in

less than 10µs.

Protection and Monitoring Features

Trace 4 - 5V Supply Voltage (2V/div.)

Trace 3 - Soft Start Timing Capacitor (1V/div.)

Trace 2 - Inductor Switching Node (2V/div.)

Figure 10: CS5156 demonstration board hiccup mode short circuit pro-

tection. Gate pulses are delivered while the soft start capacitor charges,

and cease during discharge.

VCC1 Monitor

To maintain predictable startup and shutdown characteris-

tics an internal VCC1 monitor circuit is used to prevent the

part from operating below 3.75V minimum startup. The

VCC1 monitor comparator provides hysteresis and guaran-

tees a 3.70V minimum shutdown threshold.

Short Circuit Protection

A lossless hiccup mode short circuit protection feature is

provided, requiring only the soft start capacitor to imple-

ment. If a short circuit condition occurs (VFFB < 1V), the VFFB

low comparator sets the FAULT latch. This causes the MOS-

FET to shut off, disconnecting the regulator from its input

voltage. The soft start capacitor is then slowly discharged by

a 2µA current source until it reaches its lower 0.7V threshold.

The regulator will then attempt to restart normally, operating

in its extended off time mode with a 50% duty cycle, while

the soft start capacitor is charged with a 60µA charge current.

If the short circuit condition persists, the regulator output

will not achieve the 1V low VFFB comparator threshold

before the soft start capacitor is charged to its upper 2.5V

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 (2µA/60µA = 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 10 and 11).

Trace 4 = 5V from PC Power Supply (2V/div.)

Trace 2 = Inductor Switching Node (2V/div.)

Figure 11: Startup with regulator output shorted.

Overvoltage Protection

Overvoltage protection (OVP) is provided as result of the

normal operation of the V2™ control topology and requires

no additional external components. The control loop

responds to an overvoltage condition within 100ns, causing

the MOSFET to shut off, disconnecting the regulator from

its input voltage.

9

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