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# External Voltage Regulator Control

IP.com Disclosure Number: IPCOM000113827D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 34K

IBM

## Related People

Jeanson, MJ: AUTHOR [+2]

## Abstract

A method of allowing external voltage regulator control by only adding one resistor to the regulator circuit is disclosed. This resistor is connected to a test pin which can be used when guardbanding or stress testing the circuitry that the regulator is feeding.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

External Voltage Regulator Control

A method of allowing external voltage regulator control by only
adding one resistor to the regulator circuit is disclosed.  This
resistor is connected to a test pin which can be used when
guardbanding or stress testing the circuitry that the regulator is
feeding.

The resistor R1 is added to the existing voltage regulator
circuit as shown in the figure.  The resistor R1 is tied between the
adjust pin and an external test point.  A voltage can then be applied
to this external test point via a tester or test bed.  This voltage
will change the voltage at the adjust pin, thus changing the output
voltage of the regulator accordingly.  When nothing is tied to the
external point, the regulator works as normally intended.  The
resistor also isolates the external test point so that the regulator
is not affected by external noise on the floating test pin.

The regulator output, when the test pin is left floating, is
determined by the formula: Vo=Vr(1+R2/R1) where (Vr) is the
reference voltage.

Given the lowest value needed for the regulator output (Vo),
the following formula will generate a value for R3:
R3=R1*R2(Vo-Vr)/((R1+R2)Vr-R1*Vo)

The new output voltage is then determined by connecting a
voltage (Vt) to the test pin according to the following formula:
Vo=((R2*R3+R1*R2+R1*R3)Vr+R1*R2*Vt) / (R1*R3+R1*R2).