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IR3086AMPBF

XPHASE™ PHASE IC WITH OVP, FAULT AND OVERTEMP DETECT

International Rectifier 

IR3086APbF

Phase Delay Timing Resistors RPHASE1 and RPHASE2

The phase delay of the interleaved multiphase converter is programmed by the resistor divider connected at

RMPIN+ or RMPIN- depending on which slope of the oscillator ramp is used for the phase delay programming of

phase IC, as shown in Figure 3.

If the upslope is used, RMPIN+ pin of the phase IC should be connected to RMPOUT pin of the control IC and

RMPIN- pin should be connected to the resistor divider. When RMPOUT voltage is above the trip voltage at

RMPIN- pin, the PWM latch is set. GATEL becomes low, and GATEH becomes high after the non-overlap time.

If down slope is used, RMPIN- pin of the phase IC should be connected to RMPOUT pin of the control IC and

RMPIN+ pin should be connected to the resistor divider. When RMPOUT voltage is below the trip voltage at

RMPIN- pin, the PWM latch is set. GATEL becomes low, and GATEH becomes high after the non-overlap time.

Use VBIAS voltage as the reference for the resistor divider since the oscillator ramp magnitude from control IC

tracks VBIAS voltage. Try to avoid both edges of the oscillator ramp for better noise immunity. Determine the ratio

of the programming resistors corresponding to the desired switching frequencies and phase numbers. If the resistor

RPHASEx1 is pre-selected, the resistor RPHASEx2 is determined as:

RPHASEx2

=

RAPHASEx ∗ RPHASEx1

1 − RAPHASEx

(20)

Combined Over Temperature and Phase Delay Setting Resistors RPHASE1, RPHASE2 and RPHASE3

The over temperature setting resistor divider can be combined with the phase delay resistor divider to save one

resistor per phase.

Calculate the HOTSET threshold voltage VHOTSET corresponding to the allowed maximum temperature from

Equation (18). If the over temperature setting voltage is lower than the phase delay setting voltage,

VBIAS*RAPHASEx, connect RMPIN+ or RMPIN- pin between RPHASEx1 and RPHASEx2, and connect HOTSET pin

between RPHASEx2 and RPHASEx3. Pre-select RPHASEx1,

RPHASEx2

=

(RAPHASEx ∗VBIAS − VHOTSET ) * RPHASEx1

VBIAS ∗ (1 − RAPHASEx )

(21)

RPHASEx3

=

VHOTSET ∗ RPHASEx1

VBIAS * (1 − RAPHASEx )

(22)

If the over temperature setting voltage is higher than the phase delay setting voltage, VBIAS*RAPHASEx, connect

HOTSET pin between RPHASEx1 and RPHASEx2, and connect RMPIN+ or RMPIN- between RPHASEx2 and RPHASEx3.

Pre-select RPHASEx1,

RPHASEx2

=

(V HOTSET

− RAPHASEx ∗VBIAS ) ∗ RPHASEx1

VBIAS − VHOTSET

(23)

RPHASEx3

=

RAPHASEx ∗VBIAS * RPHASEx1

VBIAS − VHOTSET

(24)

Bootstrap Capacitor CBST

Depending on the duty cycle and gate drive current of the phase IC, a 0.1uF to 1uF capacitor 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.

Page 17 of 33

9/30/04

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