IR3522 International Rectifier, IR3522 Datasheet - Page 23

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

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DESIGN PROCEDURES - IR3522 AND IR3506 CHIPSET
IR3522 EXTERNAL COMPONENTS
All the output components are selected using one output but suitable for both unless otherwise specified.
Oscillator Resistor R
The only one oscillator of IR3522 generates square-wave pulses to synchronize the phase ICs. The switching
frequency of the each phase converter equals the PHSOUT frequency, which is set by the external resistor
R
multiplied by the phase number.
Soft Start Capacitor C
The Soft Start capacitor C
and soft stop time.
SS/DEL pin voltage controls the slew rate of the converter output voltage, as shown in Figure 10. Once the
ENABLE pin rises above 1.65V, there is a soft-start delay time TD1 during which SS/DEL pin is charged from
zero to 1.4V. Once SS/DEL reaches 1.4V the error amplifier output is released to allow the soft start. The soft
start time TD2 represents the time during which converter voltage rises from zero to SVID voltage (or default
voltage) and the SS/DEL pin voltage rises from 1.4V to SVID voltage plus 1.4V. Power good time, TD3, is the
time period from VR reaching the SVID voltage to the PGOOD signal being issued.
Calculate C
ROSC
, use Figure 11 to determine the R
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1600
1500
1400
1300
1200
1100
1000
SS/DEL
900
800
700
600
500
400
300
200
5
based on the required soft start time TD2.
R
SS/DEL
osc
10
SS/DEL
Figure 11 - PHSOUT Frequency vs. RROSC chart
15
programs three different time parameters, soft start delay time, soft start time,
PHSOUT FREQUENCY vs. RROSC
20
ROSC
value. The CLKOUT frequency equals the switching frequency
25
RROSC (KOhm)
30
35
40
45
50
V3.01
IR3522
55