PI2007 datasheet(10/19 Pages) VICOR

10 / 19 page



Picor Corporation • picorpower.com

PI2007

Rev 1.3

Page 10 of 19

Select the resistor (RPG) value at the minimum input

voltage to avoid a voltage drop that may reduce VVC-

SGND lower than VC under voltage lockout.

Select the value of RPG using the following equations:

Max

CLMMax

min









RPG maximum power dissipation:

CLMMin

PdR

max

)

(





Where:

min



VC pin minimum applied voltage with

respect to Vin return

max



VC pin maximum applied voltage with

respect to Vin return

CLMMax

V 

: Controller maximum clamp voltage, 12.5V

CLMMin

V 

: Controller minimum clamp voltage, 11.0V

Max

: Controller maximum bias current, use

2.0mA plus 0.1mA for margin

Example: 40V <VVC <50V

















Max

CLMMax

min





PdR

CLMMin

116

)

(

max















Alternative

Bias

Circuit

with

Device

Enable:

Constant current circuit

In a wide operating input voltage range the size of RPG

may be become large to support power dissipation. A

simple constant current circuit can be used instead of

RPG to reduce power dissipation and can be used as a

device enable.

As shown in Figure 14, the constant current circuit

consists of an NPN transistor (Q2), Zener diode DZ,

current limit resistor (RLIMIT) and Zener bias resistor

(RZ). RLIMIT and RZ can be very low power resistors

and Q2 is a signal transistor where its Collector-

Emitter Voltage (VCEO) is equal or greater than the

input operating voltage and supports 2.5mA at the

operating input voltage.

Figure 14: Constant current bias circuit

Pulling the Q2 base (EN) to the system return (RTN)

will turn off the transistor and the controller returns

(SGND pin and PGND pin) will float and eventually

the MOSFET will be turned off.

An open collector

device can be used to enable and disable the PI2007.

The constant current circuit should guarantee current

greater than the PI2007 maximum Quiescent current

(IVC), 2.0mA.

RLIMIT can be calculated from the following equation:

MAX

MIN

LIMIT

)

(





Where:

MIN

: Minimum Zener diode voltage

)

(on

: Q2 Base-Emitter On maximum voltage, for

default use

)

(on

=0.7V

MAX

: PI2007 Quiescent Current, maximum

IVC=2.0mA

Zener Diode Selection:

Select a Zener diode with a low reverse current

requirement to minimize RZ. Zener diodes with higher

break down voltage will have lower reverse current

and reduce Q2 collector current variation.

Zener

diodes with a breakdown voltage of 6V and higher will

require

low

bias

current

and

accurate

voltage

breakdown.

RZ maximum value can be calculated with the

following equation:

Note that the surface mount resistors have limited

operating voltage capability.

Be sure to pick a

resistor package that can meet the maximum

operating voltage (Vin).

PI2007 Datasheet(PDF) 10 Page - Vicor Corporation

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