IR3522 International Rectifier, IR3522 Datasheet - Page 11

• Manufacturer Part Number: IR3522
• Description: DDR & VTT CONTROL IC
• Manufacturer: International Rectifier

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Lossless Average Inductor Current Sensing
Inductor current can be sensed by connecting a series RC network in parallel with the inductor and measuring the
voltage across the capacitor, as shown in Figure 6. The equation of this sensing network is,
Usually, the resistor Rcs and capacitor Ccs are chosen so that the RC time constant equals the time constant of the
inductor which is the inductance L divided by the inductor’s DCR (R
across Ccs is proportional to the current through L, and the sense circuit can be treated as if only a sense resistor
with the value of R
current, but affects the AC component of the inductor current.
methods provide no information during either load increase (low side sensing) or load decrease (high side sensing).
output voltage can be positioned to meet a load line based on real time information. Except for a sense resistor in
The advantage of sensing the inductor current versus high side or low side sensing is that actual output current
series with the inductor, this is the only sense method that can support a single cycle transient response. Other
being delivered to the load is obtained rather than peak or sampled information about the switch currents. The
PHASE IC
CLOCK
PULSE
PWMRMP
GATEH
GATEL
Page 11
EAIN
VDAC
L
was used. The mismatch of the time constants does not affect the measurement of inductor DC
Figure 6 Inductor Current Sensing and Current Sense Amplifier
STEADY-STATE
OPERATION
v
C
(
s
)
DUTY CYCLE INCREASE
DUE TO LOAD
INCREASE
Figure 5 PWM Operating Waveforms
=
CSOUT
v
L
(
s
)
Current
Sense Amp
1
+
sR
i
L
1
CS
C
DUTY CYCLE DECREASE
DUE TO VIN INCREASE
(FEED-FORWARD)
L
R
CS
CS
=
v
L
i
R
C
v
L
CS
c
L
CS
(
s
)
R
L
L
). If the two time constants match, the voltage
1
V
1
DUTY CYCLE DECREASE DUE TO LOAD
DECREASE (BODY BRAKING) OR FAULT
(VCC UV, OCP, VID FAULT)
+
O
+
C
sR
s
O
(
L
CS
C
R
L
CS
)
.
STEADY-STATE
OPERATION
V3.01
IR3522