IR3086AMTR International Rectifier, IR3086AMTR Datasheet - Page 12

• Manufacturer Part Number: IR3086AMTR
• Description: XPHASE Phase IC with OVP with fault overtemp detect. The IR3086AM Phase IC combined with an IR XPhase TM Control IC provides a full featured and flexible way to implement power solutions for the latest high performance CPUs and ASICs.
• Manufacturer: International Rectifier

Specifications of IR3086AMTR

• Package: 20-Lead MLPQ
• Circuit: X-Phase Phase IC
• Iout (a): 2.5A Gate Driver
• Pbf: PbF Option Available

IR3086A
When designing for OVP the overall system must be considered. In many cases the over-current protection of the
AC-DC or DC-DC converter supplying the multiphase converter will be triggered thus providing 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. One scenario to be careful
of is where the input voltage to the multiphase converter may be pulled below the level where the ICs can provide
adequate voltage to the low side MOSFET thus defeating OVP.
Dynamic changes in the VID code to a lower output voltage may trigger OVP. For example; a 250mV decrease in
output voltage combined with a light load condition will cause the low side MOSFETs to turn on and interfere with
TM
TM
Body Braking
. This will not cause a problem, however, as Body Braking
will resume once the output voltage is
less than 125mV above the VID voltage.
Since CSIN- pin is also used as the inductor current sensing input, it is usually connected to the local converter
output, which may be far away from the load of the multiphase converter. Excessive distribution impedance
between the converter and load may trigger OVP during normal operation. If the voltage drop across the distribution
impedance exceeds the minimum OVP comparator threshold of 100mV plus VID offset and voltage positioning, the
IR3086A can not be used. The IR3088 Phase IC without OVP should be used instead in applications with excessive
distribution impedance and very small or no AVP. For example, a converter having 25mV of VID offset, 125mV of
AVP at full load, and 100mV of drop in the distribution path at full load would be OK, since 100mV + 25mV + 125mV
= 250mV which is greater than the 100mV drop. However, a converter having 25mV of VID offset, no AVP, and
130mV of drop in the distribution path would require IR3088, since 100mV + 25mV + 0mV = 125mV which is smaller
than the 130mV drop.
Converter with programmable higher output voltage than VID voltage may also trigger OVP during normal
operation, and IR3088 should be used to replace IR3086A.
Thermal Monitoring (VRHOT)
The IR3086A senses its own die temperature and produces a voltage at the input of the VRHOT comparator that is
proportional to temperature. An external resistor divider connected from VBIAS to the HOTSET pin and ground can
be used to program the thermal trip point of the VRHOT comparator. 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.
Phase Fault
It is possible for multiphase converters to appear to be working correctly with one or more phases not functioning.
The output voltage can still be regulated and the full load current may still be delivered. However, the remaining
phase(s) will be stressed far beyond their intended design limits and are likely to fail. Loss of a phase can occur due
to poor solder connections or mounting during the manufacturing process, or can occur in the field. The most
common failure mode of a buck converter is failure of the high side MOSFET.
The IR3086A has the ability to detect if a phase stops switching and can provide this information to the system
through the PHSFLT output pin. If a phase stops switching its output current will drop to zero and the output of the
current sense amplifier will be the DACIN voltage. The Share Adjust Amplifier reacts to this by increasing the Ramp
Slope Adjust current until it exceeds the externally programmable PWM Ramp bias current. This will cause the
voltage at the PWMRMP pin to drop below its normal operating range. The Fault Comparator trips and drives the
PHSFLT output to ground when the voltage on the PWMRMP pin falls below 91% of the DACIN voltage. PHSFLT is
an open-collector output and should be pulled up to a voltage source through a resistor.
Page 12 of 33
2/13/09