Browse Prior Art Database

Digital Adjustable Linear Regulator

IP.com Disclosure Number: IPCOM000117098D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Braithwaite, KA: AUTHOR [+2]

Abstract

The conversion of a +5V power source with a tolerance which may go as low as 4.5V requires a low dropout regulator. This requirement exists in the Blue Lightning module, where the speed of the chip is a direct function of the voltage applied. The specification for voltage versus processor speed for Blue Lightning is as follows: 3.3V +/-10% to 75 MHZ 3.6V +/- 5% to 80 MHZ 4.1V +/- 2% to 100 MHZ

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Digital Adjustable Linear Regulator

      The conversion of a +5V power source with a tolerance which may
go as low as 4.5V requires a low dropout regulator.  This requirement
exists in the Blue Lightning module, where the speed of the chip is a
direct function of the voltage applied.  The specification for
voltage versus processor speed for Blue Lightning is as follows:
    3.3V +/-10% to  75 MHZ
    3.6V +/- 5% to  80 MHZ
    4.1V +/- 2% to 100 MHZ

      With the worst case input voltage of 4.5V to the regulator and
a current, 1.2A, a dropout voltage of less than 400mV is required.
The
following circuit shown in the schematic will accomplish this.

      Rds(on) for the IRFZ740 is 0.028 Ohms.  At 1.2A, we can achieve
an output voltage of approximately 4.4V maximum.  This circuit
requires a +12V source to power the MOSFET gate.  Since most PC power
supplies generate +12V, this is not usually a problem, especially
since the gate current requirements are a few milliamperes.  The
LT1431 voltage reference is used to drive the MOSFET pass device.
The use of this module allows the voltage to meet the speed required
from the Blue Lightning microprocessor.  Four programming resistors
are connected to the output by enabling the proper bit combinations
to the AV9504 Power Management Integrated Switch (PMIS).  The lower
Rds(on) of the PMIS n-channel FET switches is 0.3 Ohms typical and
0.4 Ohms maximum.  This value will enable the circuit to be adjust...