IR3088MTR datasheet(16/34 Pages) IRF

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IR3088

MAX

TOFST

NLOFST

MAX

∗

−

∗

(15)

MIN

MAX

DRP

∗

(16)

Body Braking

TM Related Resistors RBBFB and RBBDRP

The body braking

TM during Dynamic VID can be disabled by connecting BBFB pin to ground. If the feature is

enabled, Resistors RBBFB and RBBDRP are needed to restore the feedback voltage of the error amplifier after

Dynamic VID step down. Usually RBBFB and RBBDRP are chosen to match RFB and RDRP respectively.

IR3088 EXTERNAL COMPONENTS

PWM Ramp Resistor RPWMRMP and Capacitor CPWMRMP

PWM ramp is generated by connecting the resistor RPWMRMP between a voltage source and PWMRMP pin as well

as the capacitor CPWMRMP between PWMRMP and LGND. Choose the desired PWM ramp magnitude VRAMP and

the capacitor CPWMRMP in the range of 100pF and 470pF, and then calculate the resistor RPWMRMP from Equation

(17). To achieve feed-forward voltage mode control, the resistor RRAMP should be connected to the input of the

converter.

)]

ln(

)

[ln(

PWMRMP

DAC

PWMRMP

−

(17)

Inductor Current Sensing Capacitor CCS+ and Resistors RCS+ and RCS-

The DC resistance of the inductor is utilized to sense the inductor current. Usually the resistor RCS+ and capacitor

CCS+ in parallel with the inductor are chosen to match the time constant of the inductor, and therefore the voltage

across the capacitor CCS+ represents the inductor current. If the two time constants are not the same, the AC

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 RL. Pre-select the capacitor CCS+ and calculate RCS+ as

follows.

+ =

(18)

The bias current flowing out of the non-inverting input of the current sense amplifier creates a voltage drop across

RCS+, which is equivalent to an input offset voltage of the current sense amplifier. The offset affects the accuracy of

converter current signal ISHARE as well as the accuracy of the converter output voltage if adaptive voltage

positioning is adopted. To reduce the offset voltage, a resistor RCS- should be added between the amplifier inverting

input and the converter output.

− =

(19)

If RCS- is not used, RCS+ should be chosen so that the offset voltage is small enough. Usually RCS+ should be less

than 2 kΩ and therefore a larger CCS+ value is needed.

Page 16 of

9/30/04

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