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M1014 View Datasheet(PDF) - STMicroelectronics

Part Name
Description
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M1014 Datasheet PDF : 10 Pages
1 2 3 4 5 6 7 8 9 10
Principles of Operation and Application Tips
TSM1014
5 Principles of Operation and Application Tips
5.1 Voltage control
The voltage loop is controlled via a first trans-conductance operational amplifier, the resistor bridge R1,
R2, and the optocoupler which is directly connected to the output.
The relation between the values of R1 and R2 should be chosen as written in Equation 1.
R1 = R2 x VRef / (Vout - VRef)
Equation 1
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 100K(or more) would be appropriate for the resistors R1 and R2.
As an example, with R2 = 100K, Vout = 4.10V, VRef) = 1.210V, then R1 = 41.9K.
Note that if the low drop diode is 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
the above calculations by replacing Vout by (Vout + Vdrop).
5.2 Current control
The current loop is controlled via the second trans-conductance operational amplifier, the sense resistor
Rsense, and the optocoupler.
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 lower potential point of the sense resistor as shown on the following figure. The resistors of this bridge
are matched to provide the best precision possible.
The control equation verifies:
Rsense × Ilim = Vsense
Equation 2
Vsense = (--R-R---5-4----+--V---R-r--e-5-f--)
Ilim = -R----5----(--VR----r4--e--+-f----R--R--5--s-)-e--n---s--e
Equation 3
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 full load operation.
Plim = Ilim × Vsense
Equation 4
5/10
 

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