ir3500a International Rectifier Corp., ir3500a Datasheet - Page 24

• Manufacturer Part Number: ir3500a
• Description: Xphase3 Vr11.0 & Amd Pvid Control Ic
• Manufacturer: International Rectifier Corp.

which pulls error amplifier output low to turn off the converter output. At the same time IIN pin (ISHARE of phase
ICs) is pulled up to VCCL to communicate the over voltage condition to phase ICs, as shown in Figure 15. In each
phase IC, the OVP circuit overrides the normal PWM operation and will fully turn-on the low side MOSFET within
approximately 150ns. The low side MOSFET will remain on until ISHARE pin voltage drops below V(VCCL) -
800mV, which signals the end of over voltage condition. An over voltage fault condition is latched in the IR3500A
and can only be cleared by cycling power to the IR3500A VCCL.
In the event of a high side MOSFET short before power up, the OVP flag is activated with as little supply voltage as
possible, as shown in Figure 16. The VOSEN+ pin is compared against a fixed voltage of 1.73V (typical) for OVP
conditions at power-up. The ROSC/OVP pin will be pulled higher than 1.6V with VCCLDRV voltage as low as 1.8V.
An external MOSFET or comparator should be used to disable the silver box, activate a crowbar, or turn off the
supply source. The 1.8V threshold is used to prevent false over-voltage triggering caused by pre-charging of output
capacitors.
Pre-charging of converter output voltage may trigger OVP. If the converter output is pre-charged above 1.73V as
shown in Figure 17, ROSC/OVP pin voltage will be higher than 1.6V when VCCLDRV voltage reaches 1.8V.
ROSC/OVP pin voltage will be VCCLDRV-1V and rise with VCCLDRV voltage until VCCL is above UVLO threshold,
after which ROSC/OVP pin voltage will be VCCL-1V. The converter cannot start unless the over voltage condition
stops and VCCL is cycled. If the converter output is pre-charged 130mV above VDAC but lower than 1.73V, as
shown in Figure 17, the converter will soft start until SS/DEL voltage is above 3.92V (4.0V-0.08V). Then, over
voltage comparator is activated and fault latch is set.
(PHASE IC)
(PHASE IC)
OUTPUT
VOLTAGE
IIN
(ISHARE)
FAULT
LATCH
ERROR
AMPLIFIER
OUTPUT
(EAOUT)
GATEH
GATEL
(VO)
Page 24 of 47
VCCL-800 mV
VDAC
OVP
THRESHOLD
Figure 15 - Over-voltage protection during normal operation
NORMAL OPERATION
130mV
OVP CONDITION
July 3, 2008
IR3500A
AFTER
OVP