TS1051

Constant Voltage and Constant Current Controller

For Battery Chargers and Adaptors

4/9

Version: B07

Principle of Operation and Application Hints (continues)

Current Control

The current loop is controlled via the second trans-conductance operational amplifier, the sense resistor Rsense, and

the optocoupler. The control verifies as following

* Rsense x llim = Vsense

* Rsense = Vsense / llim

Ilim is the desired limited current, Vsense is the threshold voltage for the current control loop.

As an example, with llim = 1A, Vsense = -200mV, then Rsense = 200mΩ.

Note that the Rsense resistor should be chosen taking into account the maximum dissipation (Plim) through it during

full load operation.

* Plim = Vsense x llim

As an example, with llim=1A, and Vsense=200mV, Plim=200mW.

Therefore, for most adapter and battery charger applications, a quarter-watt, or half-watt resistor to make the current

sensing function is sufficient.

Vsense threshold is achieved internally by a resistor bridge tied to the Vref voltage reference. Its middle point is tied to

the positive input of the current control operational amplifier, and its foot is to be connected to lower potential point of

the senseresistor as shown on the following figure. The resistors of this bridge are matched to provide the best

precision possible. The current siking outpits of the two trans-conductance operational amplifiers are common (to the

outpit of the IC). This makes an Oring function which ensures that whenever the current or the voltage reaches too

high values, the optocoupler is activated.

The relation between the controlled current and the controlled output voltage can be described with a square

characteristic as shown in the following V/I output-power graph

Output Voltage vs. Output Current