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AN896 の電気的特性と機能

AN896のメーカーはST Microelectronicsです、この部品の機能は「A Battery Charger Using The TSM101」です。


製品の詳細 ( Datasheet PDF )

部品番号
AN896
部品説明
A Battery Charger Using The TSM101
メーカ
ST Microelectronics
ロゴ

ST Microelectronics ロゴ 




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AN896 Datasheet, AN896 PDF,ピン配置, 機能
AN896
APPLICATION NOTE
A BATTERY CHARGER USING THE TSM101
by S. LAFFONT
This technical note shows how to use the TSM101
integrated circuit with a switching mode power
supply (SMPS) to realize a battery charger.
An example of realization of a 12V Nickel-cadmium
battery charger is given.
1 - TSM101 PRESENTATION
The TSM101 integrated circuit incorporates a high
stability series band gap voltage reference, two
ORed operational amplifiers and a current source
(Figure 1)
Figure 1 : TSM101 Schematic Diagram
1 Vref 8
27
36
45
This IC compares the DC voltage and the current
level at the output of a switching power supply to
an internal reference.It provides a feedback
through an optocoupler to the PWM controller IC in
the primary side.
The controlled current generator can be used to
modify the level of current limitation by offsetting
the information coming from the current sensing
resistor.
A great majority of low or medium end power
supplies is voltage regulated by using shunt pro-
grammable voltage references like the TL431
(Figure 2).
The galvanic insulation of the control information is
done by using an opto-coupler in linear mode with
a variable photo current depending on the differ-
ence between the actual output voltage and the
desired one.
A current limitation is used to protect the power
supply against short circuits, but lacks precision.
This limitation is generally realized by sensing the
current of the power transistor, in the primary side
of the SMPS.
The role of the TSM101 is to make a fine regulation
of the output current of the SMPS and a precise
voltage limitation.
The primary current limitation is conserved and
acts as a security for a fail-safe operation if a
short-circuit occurs at the output of the charger.
2 - PRINCIPLE OF OPERATION
The current regulation loop and the voltage limita-
tion loop use an internal 1.24V band-gap voltage
reference. This voltage reference has a good pre-
cision (better than 1.5%) and exhibits a very stable
temperature behavior.
The current limitation is performed by sensing the
voltage across the low ohmic value resistor R5 and
comparing it to a fixed value set by the bridge
composed by R2 and R3 (Figure 3).
When the voltage on R5 is higher than the voltage
on R3 the output of the current loop operational
amplifier decreases. The optocoupler current in-
creases and tends to reduce the output voltage by
the way of the PWM controller.
The voltage regulation is done by comparing a part
of the output voltage (resistor bridge R6, R7 and
P1) to the voltage reference (1.24V).
If this part is higher than 1.24V, the output of the
voltage loop operational amplifier decreases.
March 1998
1/4

1 Page





AN896 pdf, ピン配列
AN896 - APPLICATION NOTE
The current regulation is effective when the voltage
drop across R5 is equal to the voltage on pin 5 of
the TSM101 (assuming that the internal current
source is disabled).
For medium currents (<1A), a voltage drop across
R5 of 200mV = Vr5 is a good value, R5 can be
realized with standard low cost 0.5W resistors in
parallel.
R5
=
Vr5
Ich
,
R5
=
0.285
(four
1.2
resistor
in
parallel)
R2 and R3 can be chosen using the following
formula :
R2 = R3 x
(Vref Vr5)
Vr5
CHARGE CONTROL
If the pin 2 is left open, the charge current is nominal
at # 700mA.
If pin 2 is connected to ground, the internal current
source is enabled, the current measurement is
off-setted by a voltage equal to :
Vr4 = Io x R4 with Io = 1.4mA
This can be used to lower the charging current or
eventually to stop the charge, if Vr4 > Vr5
In our example, the current offset is equal to 700 -
200mA = 500mA, representing a voltage offset
Vr4 = 150mV across R4.
The following values are used on the application
board :
R5 = 4 *1.20.5W in parallel
R4 = 130
R2 = 1.2k
R3 = 220
R9 = short circuit
R1 = 10k
C2 = 100nF
C5 = 100nF
C1 = output capacitor of the SMPS
C4 = 10µF
HIGH FREQUECY COMPENSATION
Two R-C devices (R9+C2 & R10+C3) are used to
stabilize the regulation at high frequencies. The
calculation of these values is not easy and is a
function of the transfer function of the SMPS.
A guess value for the capacitors C2 and C3 is
100nF.
Figure 3 : SMPS Using the TSM101
3/4


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合計 : 4 ページ
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