STMicroelectronics L6562A Evaluation Board STEVAL-ILL016V2 STEVAL-ILL016V2 STEVAL-ILL016V2 Fiche De Données

  

9/15

The current loop is controlled via the second trans-conductance operational amplifier, the 
sense resistor Rsense, and the optocoupler. The control equation verifies:

where I

lim

 is the desired limited current, and V

SENSE

 is the threshold voltage for the current 

control loop. 

As an example, with I

lim

 = 1 A, V

SENSE

 = 200 mV, then R

SENSE

 = 200 m

Ω. 

As an example, with I

lim

 = 1 A, and V

sense

 = 200 mV, P

lim

 = 200 mW.

Therefore, for most adapter and battery charger applications, a quarter-watt, or half-watt 
resistor is sufficient. V

SENSE

 threshold is made internally by a voltage divider tied to the V

ref

 

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 sense 
resistor as shown in 

The resistors of this voltage divider are matched 

to provide the best possible accuracy. The current sinking outputs of the two 
transconductance operational amplifiers are common (to the output of the IC). This makes 
an ORing function which ensures either the voltage control or the current control, driving the 
optocoupler's photodiode to transmit the feedback to the primary side.

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 diagram. 
(with the power supply of the device indipendent of the output voltage)

a)

b)

lim

sense

sense

I

V

R

=

sense

lim

sense

V

I

R

=

⋅

lim

sense

lim

I

V

P

⋅

=