PI2127 datasheet(5/19 Pages) VICOR

5 / 19 page

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Picor Corporation • picorpower.com

PI2127

Rev 1.3

Page 5 of 19

Functional Description:

The PI2127 integrated Cool-ORing product takes

advantage of two different technologies combining

an 8.5m

Ω on-state resistance (RDS(on)) N-channel

MOSFET with high density control circuitry. This

combination provides superior density, minimizing

PCB space to achieve an ideal ORing diode

function, significantly reducing power dissipation and

eliminating the need for heat sinking, while

minimizing design complexity.

The PI2127’s 8.5m

Ω on-state resistance MOSFET

used in the conduction path enables a dramatic

reduction

power

dissipation

versus

the

performance of a diode used in conventional ORing

applications due to its high forward voltage drop.

Due to the inherent characteristics of the MOSFET,

current will flow in the forward and reverse directions

while the gate remains above the gate threshold

voltage. Ideal ORing applications should not allow

reverse current flow, so the controller has to be

capable of very fast and accurate detection of

reverse current caused by input power source

failures, and very fast turn off of the gate of the

MOSFET. Once the gate voltage falls below the gate

threshold, the MOSFET is off and the body diode will

be reverse biased preventing reverse current flow

and subsequent excessive voltage droop on the

redundant bus.

Differential Amplifier:

The PI2127 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 sensitivity

to fault current. The amplifier output is connected to

the Reverse and Forward comparators.

Reverse Current Comparator: RVS

The reverse current comparator provides the critical

function in the controller, detecting negative voltage

caused by reverse current. Gate drive is enabled

when SP is 6mV higher than SN. When the SN pin

is 6mV higher than the SP pin, the reverse

comparator will force the gate discharge circuit to

turn off the MOSFET in typically 80ns and assert the

Fault (

FT ) low to report a fault condition.

The reverse comparator will hold the gate low until

the SP pin is 6mV higher than the SN pin. The

reverse comparator hysteresis is shown in Figure 3.

Figure 3: Reverse comparator hysteresis: VSP - VSN

Forward Voltage Comparator: FWD

The FWD comparator detects when a forward

voltage condition exists and SP is above 275mV

(typical) positive with respect to SN. When SP-SN is

more than 275mV, the FWD comparator will assert

the Fault (

FT ) low to report a fault condition.

Internal Voltage Regulator:

The PI2127 control circuitry and the gate driver are

biased through the S pin. An internal regulator

clamps the S voltage (VS-PG ) to 11.7V. The internal

regulator circuit has a comparator to monitor S input

with respect to the PG pin and pulls the MOSFET

GATE low when VS-PG is lower than the Under-

Voltage Threshold.

Fault Indication:

The

FT pin is an open collector NPN that will be

pulled low during following fault conditions.

Typical Condition

Indication of possible faults

Reverse:

VSP-VSN ≤ -6mV

Input supply shorted

(MOSFET turned OFF)

Forward:

VSP-VSN ≥ +275mV

Open FET, Gate short, Gate

open, or High current

(MOSFET turned ON)

Forward

VSP-VSN ≤ +6mV

Shorted FET on power-up

(MOSFET turned OFF)

UVLO

4.5V < VS-PG<7.15V

Controller not ready

(MOSFET turned OFF)

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