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TSM1014AIDT

P1-P3P4-P6P7-P9P10-P12P13-P14
DocID10694 Rev 3 7/14
TSM1014 Principles of operation and application tips
14
6 Principles of operation and application tips
6.1 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 written in Equation 1:
Equation 1
R1 = R2 x V
Ref
/ (V
out
- V
Ref
)
where V
out
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 100 K (or more) would be appropriate for the
resistors R1 and R2.
As an example, with R2 = 100 K, V
out
= 4.10 V, V
Ref
= 1.210 V, then R1 = 41.9 K.
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 V
out
by (V
out
+ V
drop
).
6.2 Current control
The current loop is controlled via the second transconductance operational amplifier, the
sense resistor R
sense
, and the optocoupler.
V
sense
threshold is achieved externally by a resistor bridge 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 Figure 4. The resistors of this bridge are matched to provide the best precision
possible.
The control equation verifies:
Equation 2
Equation 3
where I
lim
is the desired limited current, and V
sense
is the threshold voltage for the current
control loop.
Note that the R
sense
resistor should be chosen taking into account the maximum dissipation
(P
lim
) through it during full load operation.
R
sense
I
lim
V
sense
=
V
sense
R
5
V
ref
R
4
R
5
+
-------------------------=
I
lim
R
5
V
ref
R
sense

R
4
R
5
+
-------------------------------------------- -=
Principles of operation and application tips TSM1014
8/14 DocID10694 Rev 3
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 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.
Figure 4. Output voltage versus output current
6.3 Compensation
The voltage control transconductance operational amplifier can be fully compensated. Both
its output and negative input are directly accessible for external compensation components.
An example of a suitable voltage control compensation network is shown in Figure 3 on
page 3. It consists of a capacitor Cvc1 = 2.2 nF and a resistor Rcv1 = 22 K in series.
The current control transconductance operational amplifier can be fully compensated. Both
of its output and negative input are directly accessible for external compensation
components.
An example of a suitable current control compensation network is also shown in Figure 3.
It consists of a capacitor Cic1 = 2.2 nF and a resistor Ric1 = 22 K in series.
P
lim
I
lim
V
sense
=
7PVU
*PVU
7PMUBHFSFHVMBUJPO
$VSSFOUSFHVMBUJPO
54.7$$JOEFQFOEFOUQPXFSTVQQMZ
4FDPOEBSZDVSSFOUSFHVMBUJPO
54.7$$PO QPXFS PVUQVU
1SJNBSZDVSSFOUSFHVMBUJPO
".
DocID10694 Rev 3 9/14
TSM1014 Principles of operation and application tips
14
6.4 Start-up and short-circuit conditions
Under start-up or short-circuit conditions the TSM1014 is not provided with a high enough
supply voltage. This is due to the fact that the chip has its power supply line in common with
the power supply line of the system.
Therefore, the current limitation can only be ensured by the primary PWM module, which
should be chosen accordingly.
If the primary current limitation is considered not to be precise enough for the application,
then a sufficient supply for the TSM1014 has to be ensured under all conditions. For this, it
would be necessary to add some circuitry to supply the chip with a separate power line. This
can be achieved in a number of ways, including putting an additional winding on the
transformer.
6.5 Voltage clamp
Figure 6 shows how to realize a low-cost power supply for the TSM1014 (with no additional
windings). Please pay attention to the fact that in the particular case presented here, this
low-cost power supply can reach voltages as high as twice the voltage of the regulated line.
Since the absolute maximum rating of the TSM1014 supply voltage is 28 V. In the aim to
protect the TSM1014 against such high voltage values an internal Zener clamp is integrated
(see Figure 5).
Equation 5
Figure 5. Clamp voltage
R
limit
VCC V
z
–I
vz
=
7[
7
3MJNJU
7$$
*W[
54.
".
7$$
P1-P3P4-P6P7-P9P10-P12P13-P14

TSM1014AIDT

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Manufacturer:
STMicroelectronics
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Battery Management Voltage/Current Cont
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