IR3505M International Rectifier Corp., IR3505M Datasheet - Page 12

• Manufacturer Part Number: IR3505M
• Description: Xphase3 Phase Ic
• Manufacturer: International Rectifier Corp.

Over Voltage Protection (OVP)
The IR3505 includes over-voltage protection that turns on the low side MOSFET to protect the load in the event
of a shorted high-side MOSFET, converter out of regulation, or connection of the converter output to an
excessive output voltage. As shown in Figure 6, if ISHARE pin voltage is above V(VCCL) – 0.8V, which
represents over-voltage condition detected by control IC, the over-voltage latch is set. GATEL drives high and
GATEH drives low. The OVP circuit overrides the normal PWM operation and within approximately 150ns will
fully turn-on the low side MOSFET, which remains ON until ISHARE drops below V(VCCL) – 0.8V when over
voltage ends. The over voltage fault is latched in control IC and can only be reset by cycling the power to
control IC. The error amplifier output (EAIN) is pulled down by control IC and will remain low. The lower
MOSFETs alone can not clamp the output voltage however an SCR or N-MOSFET could be triggered with the
OVP output to prevent processor damage.
PWM Ramp
Every time the phase IC is powered up PWM ramp magnitude is calibrated to generate a 50 mV/% ramp for a
VCC=12V. For example, for a 15% duty ratio the ramp amplitude is 750mV for VCC=12V. Feed-forward
control is achieved because the PWM ramp varies with VCC voltage proportionally after calibration.
Debugging Mode
If CSIN+ pin is pulled up to VCCL voltage, IR3505 enters into debugging mode. Both drivers are pulled low
and ISHARE output is disconnected from the current share bus, which isolates this phase IC from other
phases. However, the phase timing from PHSIN to PHSOUT does not change.
FAULT LATCH
(CONTROL IC)
OUTPUT
VOLTAGE
ISHARE(IIN)
GATEH
GATEL
ERROR
AMPLIFIER
INPUT
(EAIN)
(VO)
Page 12 of 19
VCCL-800 mV
VDAC
OVP
THRESHOLD
Figure 6 - Over-voltage protection waveforms
NORMAL OPERATION
OVP CONDITION
Sept 26
th
IR3505
AFTER
OVP
, 2007