PI2126 datasheet(5/15 Pages) VICOR

5 / 15 page

Picor Corporation • picorpower.com

PI2126

Rev 1.1

Page 5 of 15

Functional Description:

The PI2126 integrated Cool-ORing product takes

advantage of two different technologies combining a

4.5m 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 PI2126’s 4.5mΩ on-state resistance MOSFET used in

the conduction path enables a dramatic reduction in

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, while

the gate remains enhanced above the gate threshold

voltage it will allow current to flow in the forward and

reverse directions. Ideal ORing applications do not allow

for 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 turn

off the gate of the MOSFET as quickly as possible. 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 PI2126 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 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. 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 90ns and assert the Fault (

) low with a typical

delay of 8μs to report a fault condition.

The reverse comparator will hold the gate low until the

SP pin is 6mV higher than the SN pin.

Reverse

comparator hysteresis is shown in Figure 3.

Figure 3: Reverse comparator hysteresis, the hysteresis

voltage is SP-SN

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 (

) low to report a

fault condition.

VC and Internal Voltage Regulator:

The PI2126 has a separate input VC that provides power

to the control circuitry. An internal regulator clamps the

VC voltage with respect to PG pin (VVC-PG) to 11.7V

typical.

The internal regulator circuit has a comparator to

monitor VC voltage and pulls the MOSFET Gate low when

VC is lower than the VC Under-Voltage Threshold.

The VR input pin can be connected to the input voltage

eliminating the need for an external limiter in 12V Bus

applications (10V to 14V). An internal 420Ω resistor is

connected between the VR pin and the internal regulator

VC pin.

Fault Indication:

The

pin is an open collector NPN that will be pulled

low under the 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 or

open, High current

(MOSFET turned ON)

Forward

VSP-VSN ≤ +6mV

Shorted FET on power-up

(MOSFET turned OFF)

UVLO

4.5V <

VVC-PG <7.15V

Controller not ready

(MOSFET turned OFF)

EOL

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