ncp5423dr2g ON Semiconductor, ncp5423dr2g Datasheet - Page 8

• Manufacturer Part Number: ncp5423dr2g
• Description: Dual Outofphase Synchronous Buck Controller With Current Limit
• Manufacturer: ON Semiconductor

0.40 V PWM comparator offset threshold and the artificial
ramp, the PWM comparator terminates the initial pulse.
Normal Operation
remains approximately constant as the V
maintains the regulated output voltage under steady state
conditions. Variations in supply line or output load
conditions will result in changes in duty cycle to maintain
regulation.
Gate Charge Effect on Switching Times
an important effect on the switching times of the FETs. A
finite amount of time is required to charge the effective
capacitor seen at the gate of the FET. Therefore, the rise and
fall times rise linearly with increased capacitive loading,
according to the following graphs.
Transient Response
transient response to any variations in input voltage and
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
0.45 V
8.6 V
During normal operation, the duty cycle of the gate drivers
When using the onboard gate drivers, the gate charge has
The 150 ns reaction time of the control loop provides fast
90
80
70
60
50
40
30
20
10
0
0
UVLO
Figure 5. Average Rise and Fall Times
1
Average Fall Time
Figure 4. Idealized Waveforms
STARTUP
2
3
Load (nF)
t
S
NORMAL OPERATION
4
5
Average Rise Time
2
6
control loop
NCP5422A, NCP5423
V
V
V
GATE(H)1
GATE(H)2
COMP
7
IN
FB
http://onsemi.com
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instantaneously, regulation is maintained by the output
capacitors during the time required to slew the inductor
current. For better transient response, several high
frequency and bulk output capacitors are usually used.
Out−of−Phase Synchronization
second channel is delayed by half the switching cycle. This
delay is supervised by the oscillator, which supplies a clock
signal to the second channel which is 180° out of phase with
the clock signal of the first channel.
many. Since the input current pulses are interleaved with one
another, the overlap time is reduced. The effect of this
overlap reduction is to reduce the input filter requirement,
allowing the use of smaller components. In addition, since
peak current occurs during a shorter time period, emitted
EMI is also reduced, thereby reducing shielding
requirements.
Overvoltage Protection
the normal operation of the V
no additional external components. The control loop
responds to an overvoltage condition within 150 ns, turning
off the upper MOSFET and disconnecting the regulator
from its input voltage. This results in a crowbar action to
clamp the output voltage preventing damage to the load. The
regulator remains in this state until the overvoltage
condition ceases.
Hiccup Overcurrent Protection
provided on the chip. The only external component required
is the COMP1 capacitor. Any overcurrent condition results
in the immediate shutdown of both output phases. Both the
upper and lower gate drives are driven low, turning off both
MOSFETs.
phase detects a short circuit when the voltage difference
between the two pins exceeds 70 mV and sets the fault latch.
The fault latch immediately turns off the error amplifier and
discharges both COMP capacitors. The capacitor connected
to COMP1 is discharged through a 5.0 mA current sink in
order to provide timing for the reset cycle. When COMP1
has fallen below 0.25 V, a comparator resets the fault latch
and error amplifier 1 begins to charge COMP1 with a 30 mA
source current. When COMP1 exceeds the feedback voltage
plus the PWM Comparator offset voltage, the normal
switching cycle will resume.
cycle, the overcurrent reset cycle will repeat itself until the
short circuit is removed, resulting in small hiccup output
pulses while the COMP capacitor charges, as shown in
Figure 6.
In out−of−phase synchronization, the turn−on of the
The advantages of out−of−phase synchronization are
Overvoltage Protection (OVP) is provided as a result of
A lossless hiccup mode short circuit protection feature is
A comparator between the IS+ and IS− on each output
If the short circuit condition persists through the restart
2
control method and requires