CS5165 View Datasheet(PDF) - ON Semiconductor
Part Name
Description
MFG CO.
'CS5165' PDF : 21 Pages View PDF
CS5165
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.
Trace 3− Load Current (5.0 A/10 mV/div.)
Trace 4− VOUT (100 mV/div.)
Figure 15. Output Voltage Transient Response to
a 14 A Load Pulse, 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 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)
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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