FAN53168MTC FAIRCHILD [Fairchild Semiconductor], FAN53168MTC Datasheet - Page 15

• Manufacturer Part Number: FAN53168MTC
• Description: 6-Bit VID Controlled 2-4 Phase DC-DC Controller
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

PRODUCT SPECIFICATION
Channel 1 – PWRGD
Channel 2 – V
Channel 3 – HS MOSFET V
Channel 4 – LS MOSFET V
After the limit is reached, the 3V pull-up on the DELAY pin
is disconnected, and the external delay capacitor is dis-
charged through the external resistor. A comparator monitors
the DELAY voltage and shuts off the controller when the
voltage drops below 1.8V. The current limit latch off delay
time is therefore set by the RC time constant discharging
from 3V to 1.8V. The applications section discusses the
selection of C
Because the controller continues to cycle the phases during
the latch-off delay time, if the short is removed before the
1.8V threshold is reached, the controller will return to nor-
mal operation. The recovery characteristic depends on the
state of PWRGD. If the output voltage is within the PWRGD
window, the controller resumes normal operation. However,
if short circuit has caused the output voltage to drop below
the PWRGD threshold, then a soft-start cycle is initiated.
During start-up when the output voltage is below 200mV, a
secondary current limit is active. This is necessary because
the voltage swing of CSCOMP cannot go below ground.
This secondary current limit controls the internal COMP
voltage to the PWM comparators to 2V. This will limit the
voltage drop across the low side MOSFETs through the
current balance circuitry.
REV. 1.0.0 6/9/03
Figure 2. Start-Up Waveforms, Circuit of Figure 1
DLY
OUT
Ω
and R
DLY
.
GS
GS
Channel 1 – PWRGD
Channel 2 – V
Channel 3 – CSCOMP
Channel 4 – HS MOSFET V
There is also an inherent per phase current limit that will
protect individual phases in the case where one or more
phases may stop functioning because of a faulty component.
This limit is based on the maximum normal-mode COMP
voltage.
Dynamic VID
The FAN53168 incorporates the ability to dynamically
change the VID input while the controller is running. This
allows the output voltage to change while the supply is run-
ning and supplying current to the load. This is commonly
referred to as VID-on-the-fly (OTF). A VID-OTF can occur
under either light load or heavy load conditions. The proces-
sor signals the controller by changing the VID inputs in mul-
tiple steps from the start code to the finish code. This change
can be either positive or negative.
Figure 3. Overcurrent Latch Off Waveform,
OUT
Circuit of Figure 1
GS
FAN53168
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