TSM1013(2016) Просмотр технического описания (PDF) - STMicroelectronics

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TSM1013
(Rev.:2016)

Constant voltage and constant current controller for battery chargers and adapters

STMicroelectronics 

TSM1013

Principle of operation and application hints

6

Principle of operation and application hints

6.1

6.1.1

6.1.2

Voltage and current control

Voltage control

The voltage loop is controlled via a first transconductance operational amplifier, the resistor

bridge R1, R2, and the optocoupler which is directly connected to the output.

The relation between the values of the R1 and R2 should be chosen as written in Equation 1.

Equation 1

R1 = R2 x Vref / (Vout - Vref)

Where Vout is the desired output voltage.

To avoid the discharge of the load, the resistor bridge R1, R2 should be highly resistive. For

this type of application, a total value of 100 K (or more) would be appropriate for the

resistors R1 and R2.

As an example, with R2 = 100 K , Vout = 4.10 V, Vref = 2.5 V, then R1 = 41.9 K.

Note that if the low drop diode should be inserted between the load and the voltage

regulation resistor bridge to avoid current flowing from the load through the resistor bridge,

this drop should be taken into account in Equation 1 by replacing Vout by (Vout + Vdrop).

Current control

The current loop is controlled via the second transconductance operational amplifier, the

sense resistor Rsense, and the optocoupler.

The Vsense threshold is achieved externally 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 the lower potential point of the sense resistor as

shown in Figure 4. The resistors of this bridge are matched to provide the best precision

possible.

The control equation verifies:

Equation 2

Rsense x Ilim = Vsense

Vsense = R5 x Vref / (R4 + R5)

Equation 3

Ilim = R5 x Vref / (R4 + R5) x Rsense

where Ilim is the desired limited current, and Vsense is the threshold voltage for the current

control loop.

Note that the Rsense resistor should be chosen taking into account the maximum dissipation

(Plim) through it during the full load operation.

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