IR3500VMPBF International Rectifier, IR3500VMPBF Datasheet - Page 19

• Manufacturer Part Number: IR3500VMPBF
• Description: The IR3500V Control IC combined with one or more xPhase3 Phase IC implement the control and MOSFET driver functions for a VR11.1 CPU VTT power supply.
• Manufacturer: International Rectifier

Specifications of IR3500VMPBF

• Package: 32-Lead MLPQ
• Circuit: X-Phase Control IC
• Switch Freq (khz): 250kHz to 1.5MHz
• Pbf: PbF Option Available

IR3500V
Open Voltage Loop Detection
The output voltage range of error amplifier is detected all the time to ensure the voltage loop is in regulation. If any
fault condition forces the error amplifier output above VCCL-1.08V for 8 switching cycles, the fault latch is set. The
fault latch can only be cleared by cycling power to VCCL.
Load Current Indicator Output
The VDRP pin voltage represents the average current of the converter plus the VDAC voltage. The load current
information can be retrieved by a differential amplifier that subtracts the VDAC voltage from the VDRP voltage.
Enable Input
Pulling the ENABLE pin below 0.8V sets the Fault Latch and a voltage above 0.85V enables the soft start of the
converter.
Thermal Monitoring (VRHOT)
A resistor divider including a thermistor at the HOTSET pin sets the VRHOT threshold. The thermistor is usually
placed at the temperature sensitive region of the converter, and is linearized by a series resistor. The IR3500V
compares the HOTSET pin voltage with a reference voltage of 1.6V. The VRHOT pin is an open-collector output
and should be pulled up to a voltage source through a resistor. If the thermal trip point is reached the VRHOT
output drives low. The hysteresis of the VRHOT comparator is added to eliminate toggling of VRHOT output.
Over Voltage Protection (OVP)
The output over-voltage happens during normal operation if a high side MOSFET short occurs or if output voltage is
out of regulation. The over-voltage protection comparator monitors the output of the remote sense amplifier (Vo
pin). If the Vo pin voltage exceeds VDAC by 130mV, as shown in Figure 15, the IR3500V raises the ROSC/OVP pin
voltage to V(VCCL) - 1V. This signal can be used by the host system as an indication that an over voltage event
has occurred enabling an appropriate response such as disabling the AC-DC converter. The ROSC/OVP pin can
also be connected to a thyrister in a crowbar circuit to blow an input fuse.
The over voltage condition also sets the over voltage fault latch, which pulls the error amplifier output low to turn off
the converter output. At the same time the 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, an 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 the 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 IR3500V and can only be cleared by cycling power to the
IR3500V 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.
Page 19 of 34
July 28, 2008