PI2061 datasheet(9/16 Pages) VICOR

9 / 16 page

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Picor Corporation • picorpower.com

PI2061

Rev 1.4

Page 9 of 16

Application Information

The PI2061 Cool-Switch is a wide input voltage high side

load disconnect switch.

This section describes in detail the procedure to follow

when designing with the PI2061 load disconnect switch.

Biasing sequence Functionality

When Vin is applied and the load is at zero volts, the VC

capacitor will charge via current flowing through RVC, D1,

load resistance and RPG. If the load resistance is much

lower than RPG, most of the charge and bias current flows

through the load.

As VC to SGND voltage rises above the Under-Voltage

Rising Threshold (VVCUVR) while the EN pin is High, the

controller will charge the MOSFET gate and monitor the

voltage across the sense resistor (VSP-SN). As the MOSFET

turns on, the load voltage (Vout) will rise until the MOSFET

is in RDS(on) and Vload=Vin. If the voltage across the sense

resistor (

) is higher than the High Range Overcurrent

Threshold (VOC-THH 166mV) while the load rises, the gate

will be discharged to PGND and latch off; otherwise Vout

will keep rising, D1 becomes reverse biased and the

controller bias current returns to ground through RPG.

When Vout reaches the Over Current Range switch over

threshold, the over current threshold switches to the Low

Range Over Current threshold (VOC-THL 70mV). VC will be

biased from Vout through the SN pin when Vout is a diode

drop (DBST) above VC as the load reaches Vin.

Upper and lower bias resistors should be selected to keep

PI2061 bias voltage in regulation.

Upper Side Bias Resistor selection: RVC

RVC is placed between Vin and VC to limit the current into

the clamp under a shorted load condition. This will allow

VC to regulate with respect to SGND/PDND node when the

MOSFET is in off condition and SGND/PGND node is pulled

low via D1, Rs and low load resistance.

The RVC resistor can be calculated using the following

expression:

And RVC maximum power dissipation is:

Where:

Vin minimum voltage (Vin to Rtn)

Vin maximum voltage (Vin to Rtn)

: VC maximum clamp voltage, 12.5V

: VC minimum clamp voltage, 11V

VC maximum quiescent current at startup,

use 3.0mA

D1 voltage drop, use 0.3V

0.1mA is added for margin

Lower Side Bias Resistor selection: RPG

RPG is placed between SGND/PGND and return to limit the

clamp current and allow VC regulation when the MOSFET

is in the on condition.

The RPG resistor can be calculated using the following

expression:

And RVC maximum power dissipation is:

Where:

Boot Strap diode minimum forward

voltage, use 0.8V

Boot Strap diode minimum forward

voltage, use 1.0V

VC maximum quiescent current, use

2.1mA

RVC and RPG calculation example

Vin (minimum) = 40V and Vin (maximum) = 50V

Note that in the case of a light load while the PI2061 is

disabled, a voltage will appear at Vout due to the

resistance between the VC pin and the SP and SN pins.

The approximate value will be:

Where:

Output load resistance when the load is inactive

Not Recommended for New Designs

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