CS5166 datasheet(13/25 Pages) ONSEMI

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CS5166

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reaching the output voltage specification limits. When load

current suddenly increases from its minimum level, the

output capacitor is pre−positioned +25 mV. Conversely,

when load current suddenly decreases from its maximum

level, the output capacitor is pre−positioned −25 mV (see

Figures 16, 17, and 18). 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 16. Output Voltage Transient Response to

a 14 A Load Pulse, VOUT = +2.825 V (DAC = 10111)

Trace 4− VOUT (100 mV/div.)

Trace 3− Load Current (5.0 A/10 mV/div.)

Figure 17. Output Voltage Transient Response to a

14 A Load Step, VOUT = +2.825 V (DAC = 10111)

Trace 1− GATE(H) (10 V/div.)

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

Trace 3− Load Current (5.0 A/div)

Trace 4− VOUT (100 mV/div.)

Figure 18. Output Voltage Transient Response to a

14 A Load Turn−Off, VOUT = +2.825 V (DAC = 10111)

Trace 1− GATE(H) (10 V/div.)

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

Trace 3− Load Current (5.0 A/div)

Trace 4− VOUT (100 mV/div.)

Power Supply Sequencing

The CS5166 offers inherent protection from undefined

start up conditions, regardless of the 12 V and 5.0 V supply

power up sequencing. The turn on slew rates of the 12 V and

5.0 V power supplies can be varied over wide ranges without

affecting the output voltage or causing detrimental effects to

the buck regulator.

PROTECTION AND MONITORING FEATURES

Overcurrent Protection

A loss−less hiccup mode current limit protection feature

is provided, requiring only the Soft Start capacitor to

implement. The CS5166 provides overcurrent protection by

sensing the current through a “Droop” resistor, using an

internal current sense comparator. The comparator

compares this voltage drop to an internal reference voltage

of 76 mV (typical).

If the voltage drop across the “Droop” resistor exceeds

this threshold, the current sense comparator allows the fault

latch to be set. This causes the regulator to stop switching.

During this overcurrent condition, the CS5166 stays off for

the time it takes the Soft Start capacitor to slowly discharge

by a 2.0 μA current source until it reaches its lower 0.7 V

threshold.

At that time the regulator attempts to restart normally by

delivering short gate pulses to both FET’s. The CS5166 will

operate initially in its extended off time mode with a 50%

duty cycle, while the Soft Start capacitor is charged with a

60 mA charge current. The gates will switch on while the

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