NCP5331_05 ONSEMI [ON Semiconductor], NCP5331_05 Datasheet - Page 19

• Manufacturer Part Number: NCP5331_05
• Description: Two-Phase PWM Controller with Integrated Gate Drivers
• Manufacturer: ONSEMI [ON Semiconductor]

grounded (but V
by increasing the duty cycle. Of course, this will cause V
to rise. When V
circuit will be activated and the overcurrent/overvoltage latch
will be set. This latch will discharge COMP, turn OFF the
upper MOSFETs, and turn ON the lower MOSFETs. The
overcurrent/overvoltage latch will hold the controller in this
state until the input power is cycled.
Transient Response and Adaptive Positioning
filter is frequently sized larger than ripple currents require in
order to reduce voltage excursions during load transients.
Adaptive voltage positioning can reduce peak−to−peak
output voltage deviations during load transients and allow
for a smaller output filter. The output voltage can be set
higher than nominal at light loads to reduce output voltage
sag when the load current is applied. Similarly, the output
voltage can be set lower than nominal during heavy loads to
reduce overshoot when the load current is removed. For low
current applications a droop resistor can provide fast
accurate adaptive positioning. However, at high currents the
loss in a droop resistor becomes excessive. For example; in
a 50 A converter a 1 mW resistor to provide a 50 mV change
in output voltage between no load and full load would
dissipate 2.5 W.
droop resistor, but must respond to changes in load current.
Figure 25 shows how adaptive positioning works. The
waveform labeled “Normal” shows a converter without
adaptive positioning. On the left, the output voltage sags
when the output current is stepped up and later overshoots
when current is stepped back down. With fast (ideal)
adaptive positioning the peak to peak excursions are cut in
half. In the slow adaptive positioning waveform the output
voltage is not repositioned quickly enough after current is
stepped up and the upper limit is exceeded.
NOTE:
If the voltage feedback signal (COREFB+) is accidentally
For applications with fast transient currents the output
Lossless adaptive positioning is an alternative to using a
Figure 22. NCP5331 Prevents Overvoltage at 0 A
The NCP5331 maintains V
upper MOSFET shorts during no−load operation.
CORE
CORE
is not), the error amplifier will respond
reaches 2.0 V, the internal crowbar
CORE
< 2.2 V when an
http://onsemi.com
CORE
NCP5331
19
voltage based on the output current of the converter. (Refer
to the application schematic in Figure 1). To set the no−load
positioning, a resistor is placed between the output voltage
and V
across the resistor to adjust the no−load output voltage. The
V
in the data sheets.
NOTE:
NOTE:
Figure 24. NCP5331 Prevents Overvoltage at Startup
FB
The controller can be configured to adjust the output
Figure 23. NCP5331 Prevents Overvoltage at 45 A
bias current is dependent on the value of R
FB
The NCP5331 maintains V
upper MOSFET shorts with 45 A loading.
The NCP5331 maintains V
upper MOSFET is shorted and ATX power is applied.
pin. The V
Figure 25. Adaptive Positioning
Normal
Slow
Limits
Fast
Adaptive Positioning
Adaptive Positioning
FB
bias current will develop a voltage
CORE
CORE
< 2.2 V when an
< 2.2 V when an
OSC
as shown