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ShowsTolerance

bq24401

SLUS497A – SEPTEMBER 2001 – REVISED MARCH 2010

www.ti.com

the trickle maintenance charge state, per Figure 2. In fast charge, when the voltage on the TS pin is higher than

Rate of Temperature Rise

The bq24401 uses a rate of temperature rise (

ΔT/Δt) scheme to terminate fast charge for NiCd and NiMH

batteries. During fast charge, it samples the TS pin voltage every 8 seconds and compares it to the value

(V/min). Figure 4 shows a typical connection diagram. In preparation for sampling the TS pin voltage, the

bq24401 briefly turns off most circuits (the MOD and RC pins will both go low) in order to get the cleanest

possible, noise-free measurement. While the monitoring of the TS pin voltage is continuous, the sampling of the

TS pin voltage with the internal ADC only occurs during fast charge.

Top-Off and Pulse-Trickle Maintenance Charge

proceeds to either top-off or trickle maintenance charge. Top-off is optional and may be desirable on batteries

that have a tendency to terminate charge before reaching full capacity. To enable this option, the capacitance

value of the resistor connected to this pin should be less than 250k

Ω. To disable top-off, the capacitance value

should be less than 0.07µF. The tolerance of the capacitor needs to be taken into account in component

selection.

a temperature fault. During top-off, current is delivered to the battery in pulses that occur each second. The fixed

pulse width allows an average current of 1/16 of the fast charge current to be delivered to the battery every

second. The LED is always off during top-off and trickle maintenance charge.

Following top-off, the bq24401 trickle-charges the battery by enabling the MOD pin to charge at a rate of once

8

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