IR3088

Phase Fault

It is possible for multiphase converters to appear to be working correctly with one or more phases not functioning.

The output voltage can still be regulated and the full load current may still be delivered. However, the remaining

phase(s) will be stressed far beyond their intended design limits and are likely to fail. Loss of a phase can occur due

to poor solder connections or mounting during the manufacturing process, or can occur in the field. The most

common failure mode of a buck converter is failure of the high side MOSFET. The IR3088 has the ability to detect if

a phase stops switching and can provide this information to the system through the PHSFLT output pin. If a phase

stops switching its output current will drop to zero and the output of its IR3088 current sense amplifier will be the

DACIN voltage. The Share Adjust Amplifier reacts to this by increasing the Ramp Slope Adjust current until it

exceeds the externally programmable PWM Ramp bias current. This will cause the voltage at the PWMRMP pin to

drop below its normal operating range. The Fault Comparator trips and drives the PHSFLT output to ground when

the voltage on the PWMRMP pin falls below 91% of the DACIN voltage. PHSFLT is an open-collector output and

should be pulled up to a voltage source through a resistor.

APPLICATIONS INFORMATION

DBST

CVCC

ROCSET

DBST

CCS+

CBST

RCP

CCS-

RBIASIN

CFB

CBST

0.1uF

OSCDS

1

VID5

2

VID0

3

VID1

4

VID2

5

VID3

6

VID4

7

VBIAS

21

BBFB

20

EAOUT

19

FB

18

VDRP

17

IIN

16

OCSET

15

IR3081

CONTROL

IC

CSCOMP

CVCCL

RCS+

RVCC

CSCOMP

RCS-

RCS-

CVCC

CVCCL

RCS+

RCS-

CSCOMP

RSHARE

RFB

CIN

RVDAC

CVDAC

CIN

CCS+

RMPIN+

1

RMPIN-

2

GATEH

14

VCCH

15

HOTSET

3

VRHOT

4

PGND

13

GATEL

12

ISHARE

5

VCCL

11

IR3088

PHASE

IC

CCS-

RMPIN+

1

RMPIN-

2

GATEH

14

VCCH

15

HOTSET

3

VRHOT

4

PGND

13

GATEL

12

ISHARE

5

VCCL

11

IR3088

PHASE

IC

CCS-

RVCC

RFB1

CVCCL

RBIASIN

RFB21

ROSC

RVCC

RPWMRMP

RBIASIN

DBST

CCS+

RPWMRMP

0.1uF

CVCC

RCS+

CVCC

CCP1

RFB22

RMPIN+

1

RMPIN-

2

GATEH

14

VCCH

15

HOTSET

3

VRHOT

4

PGND

13

GATEL

12

ISHARE

5

VCCL

11

IR3088

PHASE

IC

CBST

CCP

CIN

RPWMRMP

10 ohm

RVCC

POWERGOOD

VOUT SENSE-

12V

VID3

VID0

VID4

VID5

ENABLE

VID2

VRHOT

VID1

VOUT+

VOUT SENSE+

VOUT-

PHASE FAULT

DISTRIBUTION

IMPEDANCE

COUT

1nF

Figure 7. IR3081/3088 12V to 2.5V 3 Phase Converter

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