SEA05 datasheet(6/10 Pages) STMICROELECTRONICS

6 / 10 page

Voltage and current control

SEA05

6/10

Doc ID 17014 Rev 1

Voltage and current control

6.1

Voltage control

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

divider R1, R2, and the optocoupler which is directly connected to the output. Its possible to

choose the values of R1 and R2 resistors using Equation 1-2:

Equation 1

Equation 2

where Vo is the desired output voltage.

As an example, with R1 = 100 k

Ω and R2 = 15 kΩ Vo = 19.17 V

6.2

Current control

The current loop is controlled via the second trans-conductance operational amplifier, the

sense resistor Rsense, and the optocoupler. The control equation verifies:

Equation 3

Equation 4

where Iomax is the desired limited current, and Vcsth is the threshold voltage for the current

control loop.

As an example, with Iomax = 1 A, Vcsth = 50 mV, then Rsense = 50 m Ω.

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

(Plim) through it during full load operation.

Equation 5

As an example, with Iomax = 1 A, and Vcsth = 50 mV, Plim = 50 mW.

Therefore, for most adaptor and battery charger applications, it is suitable a low power

resistor to make the current sensing function.

)

(

Vctrl

∗

Vctrl

)

Vctrl

(

−

∗

Vcsth

max

sense

∗

max

sense

Vcsth

Lim

csth

omax

⋅

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