CS5161, CS5161H

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capacitor charging to its final value. Its voltage is limited by

the Soft Start COMP clamp and the voltage on the Soft Start

pin (see Figures 4 and 5).

Figure 4. CS5161/5161H Startup in Response to

Increasing 12 V and 5.0 V Input Voltages. Extended Off

Time is Followed by Normal Off Time Operation when

Output Voltage Achieves Regulation to the Error

Amplifier Output.

M 250 μs

Trace 3− 12 V Input (VCC1 and VCC2) (5.0 V/div.)

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

Trace 4− 5.0 V Input (1.0 V/div.)

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

Figure 5. CS5161/5161H Startup Waveforms

M 2.50 ms

Trace 3− COMP PIn (error amplifier output) (1.0 V/div.)

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

Trace 4− Soft Start Pin (2.0 V/div.)

If the input voltage rises quickly, or the regulator output

is enabled externally, output voltage will increase to the

level set by the error amplifier output more rapidly, usually

within a couple of cycles (see Figure 6).

Figure 6. CS5161/5161H Enable Startup Waveforms

M 10.0 μs

Trace 1− Regulator Output Voltage (5.0 V/div.)

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

Normal Operation

During normal operation, switch off time is constant and

changes in regulator switching frequency, duty cycle, and

output ripple in response to changes in load and line. Output

voltage ripple will be determined by inductor ripple current

working into the ESR of the output capacitors (see Figures

7 and 8).

Figure 7. CS5161/5161H Peak−to−Peak Ripple on

M 1.00 μs

Trace 1− Regulator Output Voltage (10 mV/div.)

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