ir3500 International Rectifier Corp., ir3500 Datasheet - Page 26

• Manufacturer Part Number: ir3500
• 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
The IR3500 checks for open remote sense lines every time it is enabled and will not power on if there is an open
sense line fault. If either remote sense line VOSEN+ or VOSEN- or both are open, the output of the remote sense
amplifier (VO) drops. The IR3500 monitors its VO pin voltage continuously during normal operation. If the 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 the error amplifier output low immediately and shuts 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)
June 12, 2007
IR3500