PS501 datasheet(26/42 Pages) MICROCHIP

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PS501

DS21818C-page 26

 2004 Microchip Technology Inc.

TABLE 9-2:

CAPACITY CALCULATIONS

Parameter

Name

Bytes

Lower

Limit

Upper

Limit

Typical

Value

Operational Description

CurrError

255

Current measurement error. This is the error due to the

accuracy of the A/D converter to measure and integrate the

current, 255 = 24.9%.

Cycles

65535

SBData register for CycleCount. Cycles is updated to keep

track of the total usage of the battery. Cycles is increased

whenever an amount of charge has been delivered to or

removed from the battery, equivalent to the full capacity. For a

4000 mAh battery, Cycles is increased every time 4000 mAh

goes through the battery terminals in any direction.

InitialCap

65535

2048

The initial capacity of the battery. When the PS501 is first

powered up and initialized, before a learning cycle takes place

to learn the full capacity, the full capacity will take the value

programmed into InitialCap to compute relative

State-Of-Charge percentage.

LowCurrError

255

Current offset for error calculation. Since the error of the A/D

converter is proportional to the level of current it is measuring,

the error term can be too low when the current is very low. For

this reason, the LowCurrError will compensate the ERR term

for low currents. LowCurrError milli-Amps are added to the

current when factoring in the error. Thus, the error is:

Error = (Current + LowCurrError) * CurrError.

NChangeState

255

State change delay filter. Delays the change between “charge

increasing” state and “charge decreasing” state based on current

direction. To avoid problems with current spikes in opposite

directions, a delay filter is built-in to control when to change from

charging status to discharging status. The current must change

directions and stay in the new direction for CST_DELAY * period

before the status is changed and capacity is increased or

decreased as a result of the new current direction.

NullCurr

255

A zero zone control is built into the PS501 so that any small

inaccuracy doesn’t actually drain the gas gauge, when in fact

the current is zero. For this reason, current less than NullCurr

mA in either direction will be measured as zero.

PwrConsumption

65535

140

Current consumption of the battery module. This is the average

current that the battery module typically draws from the battery

(255 = 1 mA).

SelfDischrgErr

255

Self-discharge error. This is the error inherent in the ability of

the self-discharge look-up tables to meet actual battery

characteristics, 255 = 100%.

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