Browse Prior Art Database

VARIABLE RATE BACKUP CELL RECHARGER

IP.com Disclosure Number: IPCOM000006439D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2002-Jan-03
Document File: 2 page(s) / 73K

Publishing Venue

Motorola

Related People

James E. Berry: AUTHOR [+2]

Abstract

Many products today arc implementing volatile memory systems with rechargeable battery backup for those periods of time when the main system power sup- ply is turned off. This is especially true in systems where main cell battery life is a critical concern, such as in a digital pager. Since the products on time may be rela- tively short (i.e., the length of one business day or less), it is required for the backup source to be charged to its full potential as soon as possible. Under certain condi- tions, such as the case when the backup ceil is deeply discharged, conditions may arise that stress the current sourcing capability of the memory's main power source. For instance if the backup cell is recharging from a deep discharge, the system may be required to speed up the microprocessor and at the same time turn on high cur- rent peripheral devices such as a display, memory, etc. The added current required to quickly recharge the backup cell may push the system load beyond the limi- tations of the power source. This can easily occur in systems with a low power DC/DC converter, such as in a digital pager.

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MOTOROLA INC. Technical Developments Volume 15 May 1992

VARIABLE RATE BACKUP CELL RECHARGER

by James E. Berry and Frank Fernandez

  Many products today arc implementing volatile memory systems with rechargeable battery backup for those periods of time when the main system power sup- ply is turned off. This is especially true in systems where main cell battery life is a critical concern, such as in a digital pager. Since the products on time may be rela- tively short (i.e., the length of one business day or less), it is required for the backup source to be charged to its full potential as soon as possible. Under certain condi- tions, such as the case when the backup ceil is deeply discharged, conditions may arise that stress the current sourcing capability of the memory's main power source. For instance if the backup cell is recharging from a deep discharge, the system may be required to speed up the microprocessor and at the same time turn on high cur- rent peripheral devices such as a display, memory, etc. The added current required to quickly recharge the backup cell may push the system load beyond the limi- tations of the power source. This can easily occur in systems with a low power DC/DC converter, such as in a digital pager.

  The circuit of Figure 1 allows the microprocessor to determine which of two modes will be used to recharge the backup cell. Current I1 is selected to be much larger than 12 by the relative values of Rl and R2. Using a simple I/O pin,...