ncp5215 ON Semiconductor, ncp5215 Datasheet - Page 14

• Manufacturer Part Number: ncp5215
• Description: Dual Synchronous Buck Controller For Notebook
• Manufacturer: ON Semiconductor

response enhancement circuitry is introduced to the
NCP5215.
the output voltage (COMP) of the error amplifier to detect
load transient events. As shown in Figure 1, there is a
threshold voltage in each channel made in a way that a
filtered COMP signal pluses an adjustable offset voltage,
which is set by an external resistor. Once large load
transient occurs, the COMP signal is possible to exceed the
threshold and then TRE signal will be high in a short period,
which is typically around one normal switching cycle. In
this short period, the controller will be running at high
frequency and therefore has faster response. After that the
controller comes back to normal switching frequency
operation. Figure 29 shows TRE effect on a load transient
response.
an external resistor R
to AGND.
Figure 29. Transient Response Comparison on TRE
In CCM operation, the controller continuously monitors
The internal offset voltage of the TRE threshold is set by
Top: Vo (50mV/div), Middle: Transient signal (20V/div),
Bottom: SWN (10V/div), Time: (10us/div)
(a) TRE disabled
Top: Vo (50mV/div), Middle: Transient signal (20V/div),
Bottom: SWN (10V/div), Time: (10us/div)
(b) TRE enabled
V
th_TRE
+
I
TRE
TRE
@ R
4
connected from the TRESET Pin
TRE
http://onsemi.com
(eq. 1)
NCP5215
14
where I
recommended value for V
peak-to-peak value of the COMP signal in CCM
operation. The higher V
transient. The TRE function can be disabled by pulling
high the TRESET pin to V
Adaptive Voltage Positioning (AVP)
voltage positioning can reduce peak-to-peak output
voltage deviations due to load transients and allow use of
a smaller output filter. Adaptive voltage positioning sets
output voltage higher than nominal at light loads, and
output voltage is allowed limited sag when the load current
is applied. Upon removal of the load, output voltage returns
no higher than the original level, allowing one output
transient peak to be canceled over a load stepup and release
cycle.
“Vo without AVP” shows output voltage waveform in a
converter without AVP. On the left, the output voltage sags
when the output current is stepped up and later overshoots
when current is stepped back down. With AVP, the
peak-to-peak excursions are cut around in half. The
controller can be configured to adjust the output voltage
based on the output current of the converter as shown in
Figure 31. In order to realize the AVP function, a resistor
is connected between V
conditions, the VDRP Pin voltage stays at the same voltage
level as the V
VDRP Pin voltage decreases. This causes V
according to a loadline set by the resistor.
sensed differentially. A high gain and low offset-voltage
differential
low-resistance current-sensing resistor or low-DCR
inductor to be used to minimize power dissipation. For
lossless inductor current sensing as shown in Figure 31, the
sensing RC network should satisfy
where DCR is a DC resistance of a inductor, and normally
C
cs
For applications with fast transient currents, adaptive
Figure 30 shows how AVP works. The waveform labeled
In the NCP5215, the output current of each channel is
is selected to be around 0.1 mF. In high accuracy
R
TRE
Figure 30. Adaptive Voltage Positioning
CS
is a sourcing current out the TRESET pin. A
amplifier
C
REF
V
V
CS
O
O
. As the output current increases, the
with AVP
without AVP
+
DCR
+5% x V
th_TRE
L
REF
CC
in
th_TRE
, the lower sensitivity to load
and V
O
or just leaving it float.
each
is around 1.5 times of
DRP
. During no-load
channel
OUT
to droop
allows
(eq. 2)