PI2002 datasheet(6/23 Pages) VICOR

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Picor Corporation • picorpower.com

PI2002

Rev1.1 Page 6 of 23

Functional Description:

The PI2002 controller IC product is designed to drive

back-to-back N-channel MOSFETs in Active ORing

applications that also require a load disconnect

feature.

The PI2002 used with external back-to-

back MOSFETs can function as an ideal ORing

diode in the high-side of a redundant power system

coupled with a load disconnect switch, significantly

reducing power dissipation and eliminating the need

for heatsinking.

The PI2002 provides the ability to block current in

both directions by driving two MOSFETs in a back-

to-back configuration as shown in Figure 1a.

This

configuration offers the ability to protect the load and

the MOSFET, by pulling the gate low, during

Reverse Current, Forward Over-Current, Under-

Voltage, Over-Voltage and Over-Temperature faults.

The fault flag is also issued during these fault

conditions.

Differential Amplifier:

The PI2002 integrates a high-speed low offset

voltage differential amplifier to sense the difference

between the Sense Positive (SP) pin voltage and

Sense Negative (SN) pin voltage with high accuracy.

The amplifier output is connected to three

comparators:

Reverse

comparator,

Forward

comparator, and Forward over-current comparator.

Reverse Current Comparator: RVS

The reverse current comparator provides the most

critical function in the controller, detecting negative

voltage caused by reverse current. When the SN

pin is 6mV higher than the SP pin, the reverse

comparator will enable the gate discharge circuit and

turn off the MOSFETs in typically 120ns.

The reverse comparator has typically 3mV of

hysteresis referenced to SP-SN.

Forward Current Comparator: FWD

The FWD comparator detects when a forward

current condition exists and SP is 5mV (typical)

positive with respect to SN. When SP-SN is less

than 5mV it will indicate a fault condition on the

FT pin during a light load while maintaining gate

drive to the MOSFETs. The PI2002 will initiate a

gate shutdown if the Forward “AND” the over-voltage

(OV) condition are true.

Forward Over-Current Comparator: FOC

The FOC comparator indicates an excessive forward

current condition when SP is 112mV higher than SN.

The PI2002 controller will initiate a fault condition

when the GATE output voltage is more than 45% of

the regulated gate to SN voltage and SP-SN is

higher than 112mV, the MOSFETs will turn off then

retry after a controlled off-time determined by the

capacitor value on the OCT input pins.

Over-Current Timer: OCT

OCT off-time is set by the OCT a capacitor as shown

in Figure 3.

The OCT block will control the off-time of the

MOSFETs after a FOC fault condition has occurred.

The equivalent block diagram is shown in Figure 2.

As the Set input at the OCT timer goes high,

Out

will go low, pulling the GATE pin low. At the same

time a one shot of 40µs discharges the OCT

capacitor, then releases it charging the capacitor

again.

Out and GATE pins stay low until the OCT

pin reaches the OCT high threshold (VOCT-Hi), then

Out goes high and the GATE pin sources current to

charge the MOSFET gates. As soon as the GATE

voltage reaches 45% of the GATE to SN clamp

voltage, or 45% of {VC-V(SN) -0.25V}, the Clamp

Detector asserts a low signal again at the NOR gate.

FOC is still low then the GATE pin will be pulled

low and will start a new off-time cycle of the Over-

Current timer.

Figure 2: OCT block and timing diagram

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