CS5165 datasheet(13/21 Pages) ONSEMI

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CS5165

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current suddenly increases from its minimum level, the

output capacitor is pre−positioned +40 mV. Conversely,

when load current suddenly decreases from its maximum

level, the output capacitor is pre−positioned −40 mV (see

Figures 15, 16, and 17). 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 15. Output Voltage Transient Response to

a 14 A Load Pulse, VOUT = +2.84 V (DAC = 10111)

Trace 4− VOUT (100 mV/div.)

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

Figure 16. Output Voltage Transient Response to a

14 A Load Step, VOUT = +2.84 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 17. Output Voltage Transient Response to a 14

A Load Turn−Off, VOUT = +2.84 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.)

PROTECTION AND MONITORING FEATURES

Short Circuit Protection

A lossless hiccup mode short circuit protection feature is

provided, requiring only the Soft Start capacitor to

implement. If a short circuit condition occurs the VFB low

comparator sets the FAULT latch. This causes the top FET

to shut off, disconnecting the regulator from it’s input

voltage. The Soft Start capacitor is then slowly discharged

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

threshold. The regulator will then attempt to restart

normally, operating in it’s extended off time mode with a

50% duty cycle, while the Soft Start capacitor is charged

with a 60 μA charge current.

If the short circuit condition persists, the regulator output

will not achieve the 1.0 V low VFB comparator threshold

before the Soft Start capacitor is charged to it’s upper 2.5 V

threshold. If this happens the cycle will repeat itself until the

short is removed. The Soft Start charge/discharge current

ratio sets the duty cycle for the pulses (2.0 μA/60 μA =

3.3%), while actual duty cycle is half that due to the

extended off time mode (1.65%).

This protection feature results in less stress to the

regulator components, input power supply, and PC board

traces than occurs with constant current limit protection (see

Figures 18 and 19).

If the short circuit condition is removed, output voltage

will rise above the 1.0 V level, preventing the FAULT latch

from being set, allowing normal operation to resume.

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