IR3522 International Rectifier, IR3522 Datasheet - Page 25

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

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IR3506 EXTERNAL COMPONENTS
Inductor Current Sensing Capacitor C
The DC resistance of the inductor is utilized to sense the inductor current. Usually the resistor R
C
across the capacitor C
component of the capacitor voltage is different from that of the real inductor current. The time constant mismatch
does not affect the average current sharing among the multiple phases, but affect the current signal ISHARE as
well as the output voltage during the load current transient if adaptive voltage positioning is adopted.
Measure the inductance L and the inductor DC resistance R
follows.
Bootstrap Capacitor C
Depending on the duty cycle and gate drive current of the phase IC, a capacitor in the range of 0.1uF to 1uF is
needed for the bootstrap circuit.
Decoupling Capacitors for Phase IC
0.1uF-1uF decoupling capacitors are required at VCC and VCCL pins of phase ICs.
Type III Compensation
Choose the crossover frequency fc between 1/10 and 1/5 of the switching frequency per phase, the desired
phase margin θc and Rfb1 (see Figure 12). Determine the component values based on the equations below. wc is
2*π*fc (the crossover angular frequency), Le is the equivalent inductance of the converter, C is the output
capacitance, Rst is the total equivalent resistance in series with the inductor, Rc is the output capacitance ESR
and R is the load resistance.
CS
in parallel with the inductor are chosen to match the time constant of the inductor, and therefore the voltage
Page 25
Rfb
Ccp
Rcp
Ccp
Cfb
2
1
CS
=
=
=
=
BST
=
R
Ccp
wz
CS
wp
K
represents the inductor current. If the two time constants are not the same, the AC
wp
⋅
2
=
1
1
Rfb
1
2
1
1
⋅
⋅
⋅
L
1
C
Cfb
wz
Rfb
⋅
Rcp
CS
R
1
1
L
1
CS
and Resistor R
CS
L
. Pre-select the capacitor C
CS
(11)
(13)
(15)
(16)
(12)
(14)
and calculate R
CS
V3.01
IR3522
and capacitor
CS
as