IR3513Z International Rectifier Corp., IR3513Z Datasheet - Page 23

• Manufacturer Part Number: IR3513Z
• Description: Xphase3tm Pol Control Ic
• Manufacturer: International Rectifier Corp.

IR3513Z
During a MARGIN up to a MARGIN down event (80mV excursion on VREF), OVP may be triggered since the OVP
threshold is a fixed 85mV above VREF. This can occur due to large output capacitance and light/no load operation
where the output voltage remains high while the OVP threshold falls.
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.
Error Amplifier Head Room Control
In high converter output voltage applications, there may not be enough head room in error amplifier and current sense
amplifiers of phase ICs when VCC is just above UVLO start and stop thresholds. A head room control circuit is
implemented to ensure V(VCC) – V(VO) > 2.5V by sourcing extra current to the resistor connecting to FB pin. When this
circuit is activated, the converter voltage is lower than the required and therefore the PG is also driven low.
Open Remote Sense Line Protection
If either remote sense line VOSEN+ or VOSEN- or both is open, the output of remote sense amplifier (VOUT) drops.
The IR3513Z monitors VO pin voltage continuously. If VOUT 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 400mV 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. SS/DEL voltage is discharged, and the fault latch can only be reset by cycling VCCL
power.
Open Daisy Chain Protection
IR3513Z checks the daisy chain every time it powers up. It starts a daisy chain pulse on the PHSOUT pin and detects
the feedback at PHSIN pin. If no pulse comes back after 30 CLKOUT pulses, the pulse is restarted again. If the pulse
fails to come back the second time, the open daisy chain fault is registered, and SS/DEL is not allowed to charge. The
fault latch can only be reset by cycling the power to VCCL.
After powering up, the IR3513Z monitors PHSIN pin for a phase input pulse equal or less than the number of phases
detected. If PHSIN pulse does not return within the number of phases in the converter, another pulse is started on
PHSOUT pin. If the second started PHSOUT pulse does not return on PHSIN, an open daisy chain fault is registered.
Phase Number Determination
After a daisy chain pulse is started, the IR3513Z checks the timing of the input pulse at PHSIN pin to determine the
phase number.
Output Voltage Under-voltage Monitoring
The IR3513Z compares the FB pin to a voltage, V, equal to 0.897×Vref. If the FB pin is 50mV (typical) below the
aforementioned V, the output voltage under-voltage monitor will trigger, pulling the PG pin low. The output voltage
under-voltage monitor does not effect switching of the phases or soft start.
Page 23
May 11, 2009