TSM1011 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
TSM1011
STMicroelectronics
'TSM1011' PDF : 14 Pages View PDF
Voltage and Current Control
TSM1011
5 VOLTAGE AND CURRENT CONTROL
5.1 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 relative values of R1 and R2 should be
chosen in accordance with Equation 1:
R1
=
R2
⋅
V----o---u--V-t---–r--e--V-f----r--e--f
Equation 1
where Vout is the desired output voltage.
To avoid discharge of the load, the resistor bridge
R1, R2 should have high impedance. For this type
of application, a total value of 100kΩ (or more)
would be appropriate for the resistors R1 and R2.
For example, if R2 = 100kΩ, Vout = 4.10V,
Vref=2.5V, then R1 = 41.9KΩ.
Note:
If the low drop diode is to 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 the above calculations by replacing
Vout by (Vout + Vdrop).
5.2 Current control
The current loop is controlled via the second
transconductance 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 midpoint 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 Figure 3. The
resistors of this bridge are matched to provide the
best precision possible.
The control equation verifies that:
Rsense ⋅ Ilim = Vsense
Vsense = R5 ⋅ R-----4-V---+-r--e--R-f----5-
Equation 2
Ilim = (---R----4----+---R--R--5---5-⋅--)-V--⋅---rR-e---f-s---e---n---s--e- Equation 2’
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 = Vsense ⋅ Ilim
Equation 3
Therefore, for most adapter and battery charger
applications, a quarter-watt, or half-watt resistor to
make the current sensing function is sufficient.
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 that whenever the
current or the voltage reaches too high values, the
optocoupler is activated.
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 graph.
Fig. 3: Output voltage versus output current
Vout
Voltage regulation
TSM1011 Vcc : independent power supply
0 Secondary current regulation
TSM1011 Vcc : On power output
Primary current regulation
Iout
5/9
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