IR3088A(2004) View Datasheet(PDF) - International Rectifier

Part Name

Description

MFG CO.

IR3088A
(Rev.:2004)

XPHASE™ PHASE IC WITH FAULT AND OVERTEMP DETECT

International Rectifier 

IR3088A

Over Temperature Setting Resistors RHOTSET1 and RHOTSET2

The threshold voltage of VRHOT comparator is proportional to the die temperature TJ (ºC) of phase IC. Determine

the relationship between the die temperature of phase IC and the temperature of the power converter according to

the power loss, PCB layout and airflow etc, and then calculate HOTSET threshold voltage corresponding to the

allowed maximum temperature from Equation (20).

VHOTSET = 4.73 *10−3 *TJ + 1.241

(20)

There are two ways to set the over temperature threshold, central setting and local setting. In the central setting,

only one resistor divider is used, and the setting voltage is connected to HOTSET pins of all the phase ICs. To

reduce the influence of noise on the accuracy of over temperature setting, a 0.1uF capacitor should be placed next

to HOTSET pin of each phase IC. In the local setting, a resistor divider per phase is needed, and the setting voltage

is connected to HOTSET pin of each phase. The 0.1uF decoupling capacitor is not necessary. Use VBIAS as the

reference voltage. If RHOTSET1 is pre-selected, RHOTSET2 can be calculated as follows.

RHOTSET 2

=

RHOTSET1 ∗VHOTSET

VBIAS − VHOTSET

(21)

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

(22)

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 (20). 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 )

(23)

RPHASEx3

=

VHOTSET ∗ RPHASEx1

VBIAS * (1 − RAPHASEx )

(24)

Page 17 of 34

9/30/04

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