IR3523

Page 21 of 37

June 20, 2008

Enable Input

Pulling the ENABLE pin below 1.0 V sets the Fault Latch. Forcing ENABLE to a voltage above 1.65V results in the

fault conditions are present.

Over Voltage Protection (OVP)

Output over-voltage might occur due to a high side MOSFET short or if the output voltage sense path is

125mV, the over voltage fault latch is set which pulls the error amplifier output low turning off both converters power

stage. The IR3523 communicates an OVP condition to the system by raising the ROSC pin voltage to within

V(VCCL) – 1.2 V. An OVP condition is also communicated to the phase ICs by forcing the IIN pin (which is tied to

the ISHARE bus and ISHARE pins of the phase ICs) to VCCL as shown in Figure 14. In each phase IC, the OVP

circuit overrides the normal PWM operation to ensure the low side MOSFET turn-on within approximately 130ns.

The low side MOSFET will remain on until the ISHARE pins fall below V(VCCL) - 800mV. An over voltage fault

condition is latched in the IR3523 and can only be cleared by cycling the power to VCCL.

During dynamic VID down at light to no load, false OVP triggering is prevented by increasing the OVP threshold to a

fixed 1.2 V (VOUT1) and 1.8 V (VOUT2) whenever a dynamic VID is detected and the difference between output

voltage and the fast internal VDAC is more than 50mV, as shown in Figure 15. The over-voltage threshold is

changed back to VDAC+125mV if the difference between output voltage and the fast internal VDAC is less than

50mV.

The overall system must be considered when designing for OVP. In many cases the over-current protection of the

AC-DC or DC-DC converter supplying the multiphase converter will be triggered thus providing effective protection

without damage as long as all PCB traces and components are sized to handle the worst-case maximum current. If

this is not possible, a fuse can be added in the input supply to the multiphase converter.

AFTER

OVP

FAULT

LATCH

OUTPUT

VOLTAGE

(Vout)

OVP

THRESHOLD

IIN

(PHASE IC

ISHARE)

VCCL-800 mV

OVP CONDITION

NORMAL OPERATION

GATEH

(PHASE IC)

GATEL

(PHASE IC)

ERROR

AMPLIFIER

OUTPUT

(EAOUT)

VDAC

Figure 14 - Over-voltage protection during normal operation