PS4160

DS40235B-page 4

 2003 Microchip Technology Inc.

2.0

FUNCTIONAL DESCRIPTION

2.1

PS401 Fuel Gauge

The module fuel gauge provides State-of-Charge

(SOC) and battery status data in accordance with the

SMBus standards version 1.1. The PS401 monitors the

cell voltages, battery temperature, and current to deter-

mine SOC and battery status. The State-of-Charge

calculations are compensated for cell self discharge.

The remaining time calculation is compensated for

temperature and discharge rate. The parameters for

determining battery status flags and alarm thresholds

are all programmable as is the battery design capacity

and the battery performance model data. Please refer

to the PS401 Single Chip Battery Manager Data Sheet

(DS40238) for details on configuring the PS401.

2.2

Primary Safety

The primary safety circuit provides cell protection from

conditions of overcharge, overdischarge and over-

current. Analog IC MM1414DV from Mitsumi measures

individual cell voltages and voltage across the

discharge FET. These values are compared against

internal reference values and the gates of two

P-channel power MOSFETs are controlled based on

the comparison results.

2.3

Secondary Safety

A secondary level of safety protection is provided on

the PS4160. GPIO<6> (pin 4) of the PS401, with R25

removed and bit 2 of FLAGS1 = 0, is programmed to

provide backup overcharge protection and is activated

in the case of pack over voltage, over temperature or

charge over current. In the situation where the param-

eter being monitored is the same as that of the

MM1414 the limits are set beyond those of the

MM1414. This means that the secondary protection is

triggered only in the event the primary protection fails

to activate.

2.4

Ultimate Safety

The third level of safety protection is activated by

GPIO<7> (pin 5) of the PS401 when R23 is removed

and bit 2 of FLAGS1 = 0. This pin is activated whenever

any individual cell voltage is measured above a pro-

grammable limit that is beyond both the primary and

secondary safety limits. An N-channel MOSFET is

turned on and allows current to pass through the resis-

tive heater section of a fuse. This heating opens the

fuse, permanently disabling the pack from further

charge or discharge.

2.5

OTP EPROM Programming

To write to the OTP EPROM, an additional voltage

voltage can be obtained from the PowerInfo board and

applied to the PS4160 at connection VP (small thru-

hole) located on the small edge of the board opposite

the connector edge. Then use the utilities located on

the PS OTP page of the PowerTool software to write

new values to the PS401 OTP EPROM.

2.6

Programmable I/Os

The PS4160 features four additional pins, GPIO<3:0>

(pins 24-27), which are used to drive the LED SOC

display. GPIO<5> (pin 3), is connected to the switch

which activates the LED display. Alternately, these

GPIOs may be used for other purposes by removing

the unused LEDs, programming the pins appropriately,

and using the adjacent test points to monitor the pins.

3.0

BOARD DESCRIPTION

PCB schematics and bill of materials are included

here for

completeness.

To

download

full

size

schematic and BOM, please visit the Microchip web

site (www.microchip.com).