SEA05L

Application information

Doc ID 18462 Rev 1

7/12

Current control

The current loop is controlled via a transconductance operational amplifier, the sense

The control equation verifies:

Equation 3

Equation 4

Equation 5

Therefore, for most adaptor and battery charger applications, a low-power resistor is

suitable for the current sensing function.

reference. Its midpoint is tied to the positive input of the current control operational amplifier,

and its endpoint is connected to GND. The resistors of this voltage divider are matched to

provide the best precision possible. The current sinking outputs of the two transconductance

operational amplifiers are common (to the output of the IC). This makes an OR function

which ensures that whenever the current or the voltage reaches excessively high values, the

optocoupler is activated.

The relationship 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

(with power supply of the device independent from the output voltage).

csth

O

sense

V

I

R

=

∗

max

max

O

csth

sense

I

V

R

=

max

lim

O

csth

I

V

P

∗

=