CS5151GD16 datasheet(8/17 Pages) ONSEMI

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CS5151

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

pin (see Figures 4 and 5).

Figure 4. CS5151 Demonstration Board 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. CS5151 Demonstration Board 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. CS5151 Demonstration Board 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

set by the COFF capacitor. Switch on time is adjusted by the

V2 control loop to maintain regulation. This results in

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. Peak−to−Peak Ripple on VOUT = 2.8 V,

IOUT = 0.5 A (Light Load)

M 1.00 μs

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

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

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