Figure 5 : Precise Output Voltage Control

5.3. Higher Precision for the Voltage Control

The voltage drop through the sense resistor R5

offsets the voltage measurement. In most battery

charging applications, this offset is not taken into

account because the error is negligeable com-

pared to the end-of-charge voltage due to the fact

that the charging current value decreases drasti-

cally during the final phase of the battery charging.

But in other applications needing highest possible

precision in voltage control, another connecting

schematic is possible for TSM101 as shown on

figure 5.

In this schematic, the 0V reference is defined as

the common point between the sense resistor, the

0V Output Voltage, the foot of the resistor bridge

R6/R7, and the ground (pin 4) of the TSM101.

TSM101A(1% internal voltage reference precision)

is required in such applications.

5.4. An example of application where the

charging current is different according to the

charging phase.

The following application includes a specific recom-

mendation which requires that the charging current

should be fixed to Ich1 = 800mAin normal charging

conditions, and Ich2 = 200mA when the cell volt-

age 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 second

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

6, the status signal is determined by voltage meas-

urement, 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

TSM101/A

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