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TSM1013 Datasheet(PDF) 5 Page - STMicroelectronics

Part No. TSM1013
Description  Constant Voltage and Constant Current Controller for Battery Chargers and Adaptors
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
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TSM1013 Datasheet(HTML) 5 Page - STMicroelectronics

   
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3
VOLTAGE AND CURRENT CONTROL
3.1 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 relation between the values of R1 and R2
should be chosen as writen 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
Ω (or
more) would be appropriate for the resistors R1
and R2.
As an example, with R2 = 100K
Ω, Vout = 4.10V,
Vref = 2.5V, then R1 = 41.9K
Ω.
Note that if the low drop diode should 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).
3.2 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 x Ilim = Vsense
Equation 2
Vsense = R5*Vref/(R4+R5)
Ilim = R5*Vref/(R4+R5)*Rsense
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 = Vsense x Ilim.
Equation 4
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 trans-
connuctance 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
4
COMPENSATION
Vout
Iout
Voltage regulation
TSM1013 Vcc : independent power supply
0
Secondary current regulation
TSM1013 Vcc : On power output
Primary current regulation
TSM1013
Principle of Operation and Application Hints


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