TSM101/A

9/13

5.4. An example of application where the

charging current is different according to the

charging phase.

The following application includes a specific rec-

ommendation which requires that the charging

current should be fixed to Ich1 = 800mA in normal

charging conditions, and Ich2 = 200mA when the

cell voltage is below Vl=2.5V to optimize the cell

life-time.

Moreover, an Charging Status LED should be

switched off when the cell voltage is above

Vh=6.5V.

Figure 6 shows how this can easily be achieved

using an additional dual comparator (type LM393)

where the first operator (C1) is used to activate the

TSM101 internal current generator to offset the

current measurement thanks to R4, and the sec-

ond (C2) is used to switch the status LED off. On

figure 6, the status signal is determined by voltage

measurement, this could as well be achieved by

current measurement.

If V5 = 100mV is the maximum tolerable voltage

drop through the sense resistor R5 during normal

charging conditions, then the following calcula-

tions apply :

Current Control :

R5 = V5 / Ich1 = 0.1 / 0.8 = 0.125

R5 = 125m

Ω

R3 = 1k

Ω, R2 = 11.4kΩ

V5 = R4 x Io + R5 x Ich2, therefore, R4 = (V5 - R5

x Ich2) / Io with Io = 1.4mA

R4 = 53.6

Ω

Vref = Vl x R15 / (R14 + R15) with Vl = 2.5V and

R14 + R15 ~ 20k

Ω

R15 = R14 = 10k

Ω

Voltage Control :

Vref = Vh x R6 / (R6 + R7) with Vh = 6.5V and

R6 + R7 ~ 12kW

R6 = 2.36kW, R7 = 10kW

Vref = Vh R17 / (R16 + R17)

R17 = 10kW, R16 = 42kW

Voltage Control :

Vref = Vh x R6 / (R6 + R7) with Vh = 6.5V and

R6 + R7 ~ 12kW

R6 = 2.36kW, R7 = 10kW

Vref = Vh R17 / (R16 + R17)

R17 = 10kW, R16 = 42kW

Figure 6 : Optimized Charging Conditions