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TEA1103

Fast charge ICs for NiCd and NiMH batteries

Philips Electronics 

Philips Semiconductors

Fast charge ICs for NiCd and NiMH

batteries

Preliminary specification

TEA1103; TEA1103T;

TEA1103TS

To avoid modulation on the output voltage, the top-off

charge current is DC regulated, defined by the following

equation:

Itop – off × Rsense = Rb × 3 × 10–6

(3)

where:

ttop – off = 227 × TOD × tosc

(4)

The top-off charge current will be approximately 0.15CA,

which maximizes the charge in the battery under safe and

slow charging conditions. The top-off charge period will be

approximately one hour, so the battery will be extra

charged with approximately 0.15 Q. In this way the battery

is fully charged before the system switches over to

standby.

When pin 1 (Vstb) is connected to VS, or no NTC is

connected the system compensates the (self) discharge of

the battery by trickle charge. The trickle charge current will

be pulsating, defined by the following equation:

Itrickle × Rsense = Rb × 11----56-- × 10–6

(5)

During the non current periods at trickle charge the charge

current is regulated to zero, so that the current for a load

connected in series across the battery with the sense

resistor will be supplied by the power supply and not by the

battery.

If at pin 1 (Vstb) a reference voltage is set in accordance

with the specification, and no NTC is connected the charge

mode will switch over from current to voltage regulation

after top-off. The reference regulating voltage can be

adjusted to the battery characteristic by external resistors

connected to pin Vstb.

This reference voltage has to be selected in such a way

that it equals the rest voltage of the battery. By using

voltage regulation, the battery will not be discharged at a

load occurrence. If the Vstb input pin is floating, the

TEA1103x will apply voltage regulation at 1.325 V during

the standby mode (NiCd and NiMH). The current during

voltage regulation is limited to 0.5CA. If the battery charge

current is maximized to 0.5CA for more than 2 hours

charging will be stopped. Moreover, if the temperature

exceeds Tmax, charging will be stopped completely.

As voltage regulation is referred to one cell, the voltage on

the Vbat pin must be the battery voltage divided by the

number of cells (NiCd and NiMH).

When charging, the standby mode can only be entered

after a certain period of time depending on time-out.

To support full test of the TEA1103x at application, the

standby mode is also entered when Vbat < Vbat(l) at top-off.

Timer

The timing of the circuit is controlled by the oscillator

frequency.

The timer block defines the maximum charging time by

‘time-out’. At a fixed oscillator frequency, the time-out time

can be adapted by the Programmable Time-out Divider

(PTD) using the following equation.

ttime – out = 226 × POD × PTD × tosc

(6)

The time-out timer is put on hold by low voltage,

temperature protection and during the inhibit mode.

The Programmable Oscillator Divider (POD) enables the

oscillator frequency to be increased without affecting

the sampling time and time-out. Raising the oscillator

frequency will reduce the size of the inductive components

that are used.

At fast charging, after battery insertion, after refresh or

supply interruption, the full detector will be disabled for a

period of time to allow a proper start with flat or inverse

polarized batteries. This hold-off period is disabled at fast

charging by raising pin Vstb to above ±5 V (once).

So for test options it is possible to slip the hold-off period.

The hold-off time is defined by the following equation:

thold – off = 2–5 × ttime – out

(7)

Table 2 gives an overview of the settings of timing and

discharge/charge currents.

1999 Jan 27

8

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