IR3531 datasheet(32/39 Pages) IRF

32 / 39 page

4+1 Phase Dual Output Control IC

IR3531

March 22, 2012 | FINAL | V2.27

DESIGN PROCEDURES

IR3531 EXTERNAL COMPONENTS

Switching Frequency Setting

Use of internal oscillator mode is not recommended. Use

the SCLK input to set PWM frequency. When SCLK is used,

ROSC should be present, and selected for the per phase

switching frequency in use. The chart below shows the

relationship between the per-phase switching frequency

and the ROSC value.

Figure 17: RROSC vs. Per-phase Switching Frequency

ADDRESS AND PHASE NUMBER PROGRAMMING

RESISTORS RADDR1 AND RADDR2

The ADDR pin is multi-function: SVID addressing for Rail0

and Rail1, internal/external clock synchronization and

Turbo enable/disable is selected through this pin. Choose

RADDR2 and apply the following equation to determine

RADDR1:

100

RADDR

VDAC

RADDR





where, %VDAC is the desired percentage of VDAC found

in Table 1.

ICCP PROGRAMMING RESISTORS

RICCP1 AND RICCP2

The ICCP programming resistors are used to program the

maximum currents Rail0 and Rail1 can support. Choose

RICCP2 and follow the equation below to calculate RICCP1.

100

RICCP

VDAC

RICCP





where, %VDAC is the desired percentage of VDAC found in

Table 7.

PHASE SHEDDING IMPLEMENTATION CIRCUITS

The following is a proposed circuit to implement phase

shedding. Two signals (S1 and S2) drive logic level

MOSFETs to produce a four level PHSSHED signal.

The operation is described in Table 6.

Figure 18: Phase Shedding Implementation

TABLE 10: PHASE SHEDDING CONTROL

V(PHSSHED)

Phases

VCC

Drop 3 Phases

0.625* VCC

Drop 2 Phases

0.31* VCC

Drop 1 Phases

Drop 0 Phases

IMON AND IMON1 CAPACITORS

Use 100nF for CIMON and CIMON1 to provide an

approximate 1ms filtered time constant for current

reporting data.

VCC BIAS REGULATOR POWER STAGE

COMPONENTS

Use a 10 µH inductor with a current rating no less than 2 A.

Use a Schottky diode with operating current of 1 A or

higher and capable of withstanding 2 A for short periods of

time. A 10 µF capacitor ceramic capacitor rated for 16V is

recommended for charge storage and filtering.

IR3531 Datasheet(PDF) 32 Page - International Rectifier

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