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TEMPERATURE COMPENSATED I.C. BATTERY VOLTAGE SCALER FOR MULTI-CELL APPLICATIONS

IP.com Disclosure Number: IPCOM000005439D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2001-Oct-10
Document File: 2 page(s) / 73K

Publishing Venue

Motorola

Related People

Gary A. Oliwa: AUTHOR

Abstract

A desirable feature In an integrated circuit based device is a low battery indication. For detection of a low battery condition, the battery voltage is scaled down and compared to a regulated reference. For universality, the circuit should be usable in one, two, or three cell supply applications without the need for external discrete components.

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TEMPERATURE COMPENSATED I.C. BATTERY VOLTAGESCALER FOR MULTI-CELL APPLICATIONS

By Gary A. Oliwa

   A desirable feature In an integrated circuit based device is a low battery indication. For detection of a low battery condition, the battery voltage is scaled down and compared to a regulated reference. For universality, the circuit should be usable in one, two, or three cell supply applications without the need for external discrete components.

   Over temperature, changes in resistor values, reference voltages, and junction potentials create undesirable variations in low battery trip levels, For the processing parameters given, this circuit eliminates these variations regardless of the number of supply cells by cascading negative T.C. junction potentials with positive T.C. ion-implanted resistors.

   Referring to the circuit diagram, avoltage VREF generated by a band-gap reference circuit is applied to one side of a differential amplifier/comparator consisting of Ql, 02, and Q3. The reference voltage T.C. is - 2 mVI"C. The zero-T.C. current source consisting of IREF, Q4, and Q5 pulls current through a load Rx, and the voltage Vx is applied to the opposite side of the comparator. Since the current through RX is constant, the voltage drop across RX will be constant and the voltage VX will be a fixed amount below the supply voltage VB. The comparator will trip when the supply voltage falls below 1.1 volts times the number of cells in the supply.

   Over temperature, the value of...