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A 4-Cell Ni-Cad Regulator/Charger for Notebook Computers - Design Note 54

Design note for a notebook computer 5V regulator and 4-cell Ni-Cad charger using the LTC1155 dual MOSFET driver and LT1431 controller for high-side N-channel switching.

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Overview

This design document describes a power management system for notebook computers powered by a 4-cell Ni-Cad battery pack. It utilizes the LTC1155 dual power MOSFET driver to provide 12V of gate drive for high-side N-channel MOSFETs, eliminating the need for P-channel components. The system includes a battery charger with thermal protection via an RL-1101-100-G thermistor and a low-dropout 5V regulator controlled by the LT1431. The circuit automatically switches power from the battery to a 9V wall unit when connected and features a 3A current limit, overcurrent latch-off protection, and a low standby current of less than 10µA.

Use Cases

  • Notebook computer power systems
  • Portable electronics battery charging
  • High-side N-channel MOSFET switching
  • Low-voltage drop 5V regulator circuits
  • Ni-Cad battery pack management

Topics

LTC1155
LT1431
IRLZ24
VN2222L
MBR320
Ni-Cad Battery Charger
Low Dropout Regulator
High Side MOSFET Driver
Notebook Power Supply
Power Management IC

Referenced Parts

IRLZ24

International Rectifier

built using the new LTC1155 and three inexpensive power MOSFETs... IRLZ24

LT1431

Analog Devices

The LT1431 controls the gate of Q4 and provides a regulated 5V output when the battery is above 5V.

LTC1155

Analog Devices

The new LTC1155 dual power MOSFET driver delivers 12V of gate drive to two N-channel power MOSFETs

VN2222L

Microchip

Q1 drives an indicator lamp during quick charge... VN2222L

RL-1101-100-G

Keystone

An inexpensive thermistor, RT1... KEYSTONE RL-1101-100-G

D2-D4

Diodes

made up of diodes D2-D4 ensure that Q3 conducts all