NCP5318 ON Semiconductor, NCP5318 Datasheet - Page 28

• Manufacturer Part Number: NCP5318
• Description: Two/Three/Four-Phase Buck CPU Controller
• Manufacturer: ON Semiconductor

9. Current Sensing
different phases, to limit the maximum phase current and to
limit the maximum system current. Since the current
information is a part of the control loop, better stability is
achieved if the current information is accurate and
noise−free. The NCP5318 uses differential current sense
amplifiers to achieve the best possible performance.
Figure 29.
network (R
Current sensing is used to balance current between
Two sense lines are routed for each phase, as shown in
For inductive current sensing, choose the current sense
constant of the current sense network is too long
Figure 33. V
LOAD CURRENT, 60 A/DIV
(Slow): V
VDRP VOLTAGE,
200 mV/DIV
OUTPUT VOLTAGE,
50 mV/DIV
CSx
200 mS/DIV
, C
R CSx
CSx
DRP
DRP
, x = 1, 2, 3 or 4) to satisfy
and V
tuning waveforms. The RC time
C CSx + Lo
OUT
respond too slowly.
V
constant of the current sense network is optimal:
R L
DRP
Figure 35. V
and V
LOAD CURRENT, 60 A/DIV
OUTPUT VOLTAGE,
50 mV/DIV
VDRP VOLTAGE,
200 mV/DIV
200 mS/DIV
OUT
DRP
without overshooting.
respond to the load current quickly
(eq. 31)
http://onsemi.com
tuning waveforms. The RC time
28
where R
starting point for R
constructed, the value of R
fine−tuned in the lab by observing the V
step change in load current. Tune the R
by varying R
output pin with maximum rise time and minimal overshoot
as shown in Figure 35.
network (R
but maintain the fidelity of the triangular current waveform.
For resistive current sensing, choose the current sense
constant of the current sense network is too short
Figure 34. V
L
is the inductor ESR. This will provide an adequate
(Fast): V
CSx
OUTPUT VOLTAGE, 50 mV/DIV
LOAD CURRENT, 60 A/DIV
CSx
, C
VDRP VOLTAGE,
500 mV/DIV
CSx
to provide a “square−wave” at the V
DRP
200 mS/DIV
DRP
CSx
, x = 1, 2, 3, or 4) to reject noise spikes,
tuning waveforms. The RC time
and V
and C
CSx
OUT
CSx
(and/or C
both overshoot.
. After the converter is
CSx
DRP
x C
CSx
signal during a
CSx
) should be
network
DRP