ir3500a International Rectifier Corp., ir3500a Datasheet - Page 26

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

During dynamic VID down, OVP may be triggered when output voltage can not follow VDAC voltage change at light
load with large output capacitance. Therefore, over-voltage threshold is raised to 1.73V from VDAC+130mV
whenever dynamic VID is detected and the difference between output voltage and VDAC is more than 50mV, as
shown in Figure 19. The over-voltage threshold is changed back to VDAC+130mV if the difference is smaller 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 and provide 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.
Open Remote Sense Line Protection
If either remote sense line VOSEN+ or VOSEN- or both are open, the output of remote sense amplifier (VO) drops.
The IR3500A monitors VO pin voltage continuously. If VO voltage is lower than 200 mV, two separate pulse
currents are applied to VOSEN+ and VOSEN- pins respectively to check if the sense lines are open. If VOSEN+ is
open, a voltage higher than 90% of V(VCCL) will be present at VOSEN+ pin and the output of open line detect
comparator will be high. If VOSEN- is open, a voltage higher than 700mV will be present at VOSEN- pin and the
output of open-line-detect comparator will be high. The open sense line fault latch is set, which pulls error amplifier
output low immediately and shut down the converter. The SS/DEL voltage is discharged and the fault latch can only
be reset by cycling VCCL power.
Page 26 of 47
VCCLDRV
OUTPUT
VOLTAGE
(VOSEN+)
VCCL UVLO
ROSC/OVP
SS/DEL
VCC
Figure 18 - Over-voltage protection with pre-charging converter output VID + 0.13V <Vo < 1.73V
12V
VCCL+0.7V
VCCL+0.7V
1.73V
VID + 0.13V
VCCL - 1V
0.6V
3.92V (4V-0.08V)
July 3, 2008
IR3500A