ncp5217a ON Semiconductor, ncp5217a Datasheet - Page 10

• Manufacturer Part Number: ncp5217a
• Description: Single Synchronous Step-down Controller
• Manufacturer: ON Semiconductor

Adaptive Voltage Positioning (AVP)
voltage positioning can reduce peak−to−peak output voltage
deviations due to load transients. With the use of AVP, the
output voltage allows to have some controlled sag when load
current is applied. Upon removal of the load, the output
voltage returns no higher than the original level, just
allowing one output transient peak to be cancelled over a
load step up and release cycle. The amount of AVP is
adjustable.
are depicted at Figure 17.
For applications with fast transient currents, adaptive
The behaviors of the V
Figure 16. Transient Response with TRE Enable
DCR
Figure 18. Configuration for AVP function
Vo
Figure 17. Adaptive Voltage Positioning
Vo With AVP
Vo Without AVP
L
Top to Bottom SWN, V
Rt
Rb
Rs1
Cs
IDRP/OCP
Rocp
Rs2
CS+
CS−
FB
o
waveforms with or without AVP
+
−
o
Vref
, Transient Signal
+
+
G i
I DRP
COMP
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current path is connecting to the FB pin via R
Rocp is not actually for AVP function, indeed, R
for OCP threshold value programming. The IDRP/OCP pin
has dual functions: OCP programming and AVP. At the
IDRP/OCP pin, conceptually there is a current source which
is modulated by current sensing amplifier.
The output voltage Vo with AVP is:
Where I
set by the external divider that is
The load line impendence R
Where DCR is inductor DC resistance. Gain_CS is a gain
from [(CS+) − (CS−)] to IDRP Gain (At electrical table, the
symbol is IDRP_GAIN), the typical value is 0.525 mA/mV.
Rocp resistor into ground.
resistor Rt can affect the R
the amount of R
component value. And if the user wants to fine tune the
compensation network for optimizing the transient
performance, it is NOT recommend to adjust the value of Rt.
Otherwise, both transient performance and AVP amount
will be affected. The following diagram shows the typical
waveform of AVP. Note that the Rt typical value should be
above 1 kW.
The Figure 18 shows how to realize the AVP function. A
The AVP function can be easily disable by shorting the
From the equation we can see that the value of “top”
Top to Bottom: SWN, V
o
R
is the load current, no load output voltage Vo0 is
Figure 19. Typical waveform of AVP
LL
+ DCR * Gain_CS * Rt *
LL
V
V
FRIST before defining the compensation
O
O
0 + 1 )
+ V
o
LL
, Transient Signal (0.5−10−0.5A)
O
0 * I
, so it is recommended to define
LL
is given by:
Rb
Rt
O
* R
* V
LL
Rs1 ) Rs2
ref
Rs2
ocp
ocp
resistor.
is used
(eq. 1)
(eq. 2)
(eq. 3)