User guide

UC864-E/G/WD/WDU Hardware User Guide

1vv0300766a Rev.4

- 03/02/09

5.2.1.3. Battery Source Power Supply Design Guidelines

•

The desired nominal output for the power supply is 3.8V and the

maximum allowed voltage is 4.2V, hence a single 3.7V Li-Ion cell battery

type is suited for supplying the power to the Telit UC864-E/G/WD/WDU

module. The three cells Ni/Cd or Ni/MH 3.6 V Nom. battery types or 4V

PB types must not be used directly since their maximum voltage can rise

over the absolute maximum voltage for UC864-E/G/WD/WDU and

damage it.

• A Bypass low ESR capacitor of adequate capacity must be provided in

order to cut the current absorption peaks, a 100μF tantalum capacitor is

usually suited.

• Make sure the low ESR capacitor (usually a tantalum one) is rated at least

10V.

• A protection diode must be inserted close to the power input, in order to

save UC864-E/G/WD/WDU from power polarity inversion. Otherwise the

battery connector must be done in a way to avoid polarity inversions when

connecting the battery.

• The battery capacity must be at least 500mAh in order to withstand the

current peaks of 2A; the suggested capacity is from 500mAh to 1000mAh.

5.2.1.4. Battery Charge Control Circuitry Design Guidelines

The chargin

g process for Li-Ion Batteries can be divided into 4 phases:

• qualification and trickle charging

• fast charge 1 - constant current

• final charge - constant voltage or pulsed charging

• maintenance charge

The qualification process consists of a battery voltage measure, indicating roughly its

charge status. If the battery is deeply discharged, meaning its voltage is lower than

the trickle charging threshold, then charging must start slowly, possibly with a current

limited to the pre-charging process. The current must be kept very low with respect to

the fast charge value.

NOTE:

Do not use any Ni-Cd, Ni-MH, and Pb battery types directly connected with UC864-

E/G/WD/WDU. Their use can lead to overvoltage on UC864-E/G/WD/WDU and

damage it. Use only Li-Ion battery types.