Applications Information: continued

8

Transient Response

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

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

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

less than 10µs.

To maintain predictable startup and shutdown characteris-

part from operating below 3.75V minimum startup. The

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.)