PI2123 datasheet(6/20 Pages) VICOR

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Functional Description:

The PI2123 integrated Cool-ORing product takes

advantage of two different technologies combining a

Ω on-state resistance (Rds(on)) single 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 PI2123’s 3m

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.

This can allow for the elimination of complex heat

sinking

and

other

thermal

management

requirements. Due to the inherent characteristics of

the integrated MOSFET, while the gate remains

enhanced above the gate threshold voltage it will

allow current to flow in the forward and reverse

direction. Ideal ORing applications do not allow for

reverse current flow, so the integrated 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. During forward over-

current conditions caused by load faults, the

controller maintains gate drive to the MOSFET to

keep power dissipation as low as possible,

otherwise the inherent body diode of the MOSFET

would conduct, which has higher effective forward

drop. Conventional ORing solutions using diodes

offer no protection against forward over-current

conditions.

During

the

forward

over-current

condition, the PI2123 will provide an active-low fault

flag to the system via the fault pin. The fault flag is

also issued during the reverse current condition,

light load conditions, VC under-voltage, Input Under-

Voltage and Over-Voltage and Over-Temperature

conditions.

Differential Amplifier:

The PI2123 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 Comparator: RVS

The reverse comparator is the most critical

comparator. It looks for negative voltage caused by

reverse current. When the SN pin is 6mV higher

than the SP pin, the reverse comparator will enable

the BK current source to charge an internal 2pF

capacitor. The blanking timer provides noise filtering

for typical switching power conversion that might

cause premature reverse current detection. Once

the voltage across the capacitor reaches the timer

threshold voltage (1.25V) the MOSFET will be

turned off. The shortest blanking time is 50ns when

BK is connected to ground. The Blanking time will

be added to the controller delay time. The Electrical

Specifications in the DIFFERENTIAL AMPLIFIER

AND COMPARATOR section for Reverse Fault to

Slave Low Delay Time “tRVS-MS or tRVS-SL” is the

controller delay time plus the blanking time.

Reverse Blanking Timer: BK

Connecting an external resistor (

) between the

BK pin and ground will increase the blanking time as

shown in the following chart.

Where:

≤

200

If BK is connected to VC for slave mode operation,

then the blanking time will be about 320ns typically,

and total delay time will be 430ns.

The reverse comparator has 3mV of hysteresis

referenced to SP-SN.

If the conditions are met for a reverse current fault,

then the active-low fault flag output will also indicate

a fault to the system after the 40µs fault delay

time.

Picor Corporation • picorpower.com

PI2123

Rev 1.0

Page 6 of 20

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