CS5166 datasheet(12/25 Pages) ONSEMI

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CS5166

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Figure 13. 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 and the ESR of the output capacitors (see Figures

14 and 15).

Figure 14. Normal Operation Showing Output

Inductor Ripple Current and Output Voltage

Ripple, 0.5 A Load, VOUT = +2.825 V (DAC = 10111)

Trace 1− GATE(H) (10 V/div.)

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

Trace 3− Output Inductor Ripple Current (2.0 A/div.)

Trace 4− VOUT ripple (20 mV/div.)

Trace 1− GATE(H) (10 V/div.)

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

Trace 3− Output Inductor Ripple Current (2.0 A/div.)

Trace 4− VOUT ripple (20 mV/div.)

Figure 15. Normal Operation Showing

Output Inductor Ripple Current and Output

Voltage Ripple, ILOAD = 14 A, VOUT = +2.825 V

(DAC = 10111)

Transient Response

The CS5166 V2 control loop’s 150 ns reaction time

provides 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.

Overall load transient response is further improved

through a feature called “Adaptive Voltage Positioning”.

This technique pre−positions the output capacitors voltage

to reduce total output voltage excursions during changes in

load.

Holding tolerance to 1.0% allows the error amplifiers

reference voltage to be targeted +25 mV high without

compromising DC accuracy. A “Droop Resistor”,

implemented through a PC board trace, connects the Error

Amps feedback pin (VFB) to the output capacitors and load

and carries the output current. With no load, there is no DC

drop across this resistor, producing an output voltage

tracking the Error amps, including the +25 mV offset. When

the full load current is delivered, an 50 mV drop is developed

across this resistor. This results in output voltage being

offset −25 mV low.

The result of Adaptive Voltage Positioning is that

additional margin is provided for a load transient before

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