CS5157GD16 datasheet(8/14 Pages) CHERRY

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Applications Information: continued

Figure 6: Peak-to-peak ripple on VOUT = 2.8V, IOUT = 13A (heavy load).

Transient Response

The CS5157 V2

TM control loop’s 100ns reaction time pro-

vides unprecedented transient response to changes in input

voltage or output current. Pulse by pulse adjustment of

duty cycle is provided to quickly ramp the inductor current

to the required level. Since the inductor current cannot be

changed instantaneously, regulation is maintained by the

output capacitor(s) during the time required to slew the

inductor current.

For best transient response, a combination of a number of

high frequency and bulk output capacitors are usually

used.

If the maximum on time is exceeded while responding to a

sudden increase in load current, a normal off time occurs to

prevent saturation of the output inductor.

Figure 7: CS5157 demonstration board response to a 0.5 to 13A load

pulse (output set for 2.8V).

Figure 8: CS5157 demonstration board response to 13A load turn on

(output set for 2.8V). Upon completing a normal off time, the V2

TM con-

trol loop immediately connects the inductor to the input voltage, pro-

viding 100% duty cycle. Regulation is achieved in less than 20µs.

Figure 9: CS5157 demonstration board response to 13A load turn off

(output set for 2.8V). V2

TM control topology immediately connects

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

less than 10µs.

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.

Protection and Monitoring Features

Trace1 - Regulator Output Voltage (100mV/div.)

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

Trace 3 - Output Current (13 to 0.5 Amps) (10A/div.)

Trace 1 - Regulator Output Voltage (100mV/div.)

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

Trace 3 - Output Current (0.5 to 13 Amps) (10A/div.)

Trace 1 - Regulator Output Voltage (100mV/div.)

Trace 3 - Regulator Output Current (10A/div.)

Trace1 - Regulator Output Voltage (10mV/div.)

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

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