Page 1
VIPER12A-E
Low power offline switched-mode power supply primary switcher
Features
■ Fixed 60 kHz switching frequency
■ 9 V to 38 V wide range V
■ Current mode control
■ Auxiliary undervoltage lockout with hysteresis
■ High voltage start-up current source
■ Overtemperature, overcurrent and overvoltage
protection with auto-restart
■ Typical power capability
– European (195 - 265 Vac) 8 W for SO-8,
13 W for DIP-8
– European (85 - 265 Vac) 5 W for SO-8,
8 W for DIP-8
Description
The VIPER12A combines a dedicated current
mode PWM controller with a high voltage power
MOSFET on the same silicon chip.
voltage
DD
DIP-8SO-8
Typical applications cover off line power supplies
for battery charger adapters, standby power
supplies for TV or monitors, auxiliary supplies for
motor control, etc.
The internal control circuit offers the following
benefits: Large input voltage range on the V
accommodates changes in auxiliary supply
voltage (This feature is well adapted to battery
charger adapter configurations), automatic burst
mode in low load condition and overvoltage
protection in HICCUP mode.
DD
pin
Figure 1. Block diagram
DRAIN
ON/OFF
REGULATOR
INTERNAL
VDD
FB
8/14.5V
42V
SUPPLY
_
+
+
_
OVERTEMP.
DETECTOR
R
FF
S
OVERVOLTAGE
Q
December 2010 Doc ID 11977 Rev 2 1/21
LATCH
60kHz
OSCILLATOR
S
FF
R1
R2
R4QR3
PWM
LATCH
BLANKING
+
_
0.23 V
230 Ω
1 kΩ
SOURCE
www.st.com
21
Page 2
Contents VIPER12A-E
Contents
1 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Pin connections and function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4 Rectangular U-I output characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5 Wide range of VDD voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6 Feedback pin principle of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7 Startup sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8 Overvoltage threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9 Operation pictures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
11 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2/21 Doc ID 11977 Rev 2
Page 3
VIPER12A-E Electrical data
1 Electrical data
1.1 Maximum rating
Stressing the device above the rating listed in the “absolute maximum ratings” table may
cause permanent damage to the device. These are stress ratings only and operation of the
device at these or any other conditions above those indicated in the Operating sections of
this specification is not implied. Exposure to absolute maximum rating conditions for
extended periods may affect device reliability.
Table 1. Absolute maximum rating
Symbol Parameter Value Unit
(2)
(1)
-0.3 ... 730 V
-0.3 ... 400 V
200
1.5
V
kV
V
Switching drain source voltage (TJ = 25 ... 125 °C)
DS(sw)
Start-up drain source voltage (TJ = 25 ... 125 °C)
V
DS(st)
I
Continuous drain current Internally limited A
D
Supply voltage 0 ... 50 V
V
DD
I
Feedback current 3 mA
FB
Electrostatic discharge:
V
Machine model (R = 0 Ω; C = 200 pF)
ESD
Charged device model
Junction operating temperature Internally limited °C
T
J
Case operating temperature -40 to 150 °C
T
C
T
1. This parameter applies when the start-up current source is OFF. This is the case when the VDD voltage has
reached V
2. This parameter applies when the start up current source is ON. This is the case when the VDD voltage has
not yet reached V
Storage temperature -55 to 150 °C
stg
and remains above V
DDon
or has fallen below V
DDon
DDoff
.
.
DDoff
1.2 Thermal data
Table 2. Thermal data
Symbol Parameter SO-8 DIP-8 Unit
R
thJC
R
thJA
1. When mounted on a standard single-sided FR4 board with 200 mm2 of Cu (at least 35 µm thick) connected
to all DRAIN pins.
Thermal resistance junction-case Max 25 15 °C/W
Thermal resistance ambient-case
(1)
Max 55 45 °C/W
Doc ID 11977 Rev 2 3/21
Page 4
Electrical characteristics VIPER12A-E
2 Electrical characteristics
TJ = 25 °C, V
= 18 V, unless otherwise specified
DD
Table 3. Power section
Symbol Parameter Test conditions Min Typ Max Unit
BV
Drain-source voltage ID = 1 mA; V
DSS
I
DSS
r
DS(on)
OFF State drain
current
Static drain-source
ON state resistance
tf Fall time
Rise time
t
r
Drain capacitance V
C
OSS
1. On clamped inductive load
= 500 V; V
V
DS
TJ = 125 °C
ID = 0.2 A ID = 0.2 A; 27 30
= 0.2 A ID = 0.2 A; TJ = 100 °C 54
I
D
= 0.1 A; V
I
D
(See Figure 9 on page 13)
I
= 0.2 A; V
D
(See Figure 9 on page 13)
= 25 V 40 pF
DS
= 2 V 730 V
FB
= 2 V;
FB
= 300 V
IN
= 300 V
IN
(1)
(1)
100 ns
50 ns
0.1 mA
Ω
Table 4. Supply section
Symbol Parameter Test conditions Min Typ Max Unit
≤ 400 V;
DS
DDon
HYST
(1)
-1 mA
0 mA
4.5 mA
I
DDch
I
DDoff
I
DD0
I
DD1
Start-up charging
current
Start-up charging
current in thermal
shutdown
Operating supply
current not switching
Operating supply
current switching
100 V ≤ V
= 0 V ...V
V
DD
(See Figure 10 on page 13)
= 5 V; VDS = 100 V
V
DD
TJ > TSD - T
= 2 mA 3 5 mA
I
FB
I
= 0.5 mA; ID = 50 mA
FB
D
Restart duty-cycle (See Figure 11 on page 13) 16 %
RST
undervoltage
V
V
DDoff
V
DDon
V
DDhyst
V
DDovp
1. These test conditions obtained with a resistive load are leading to the maximum conduction time of the
device.
DD
shutdown threshold
start-up
V
DD
threshold
V
threshold
DD
hysteresis
overvoltage
V
DD
threshold
(See Figure 10,
Figure 11 on page 13)
(See Figure 10,
Figure 11 on page 13))
(See Figure 10 on page 13) 5.8 6.5 7.2 V
4/21 Doc ID 11977 Rev 2
7 8 9 V
13 14.5 16 V
38 42 46 V
Page 5
VIPER12A-E Electrical characteristics
Table 5. Oscillation section
Symbol Parameter Test conditions Min Typ Max Unit
F
Oscillator frequency
OSC
total variation
= V
V
DD
TJ = 0 ... 100 °C
DDoff
... 35 V;
54 60 66 kHz
Table 6. PWM comparator section
Symbol Parameter Test conditions Min Typ Max Unit
G
I
Dlim
I
FBsd
RFB
t
ID
d
I
to ID current gain (See Figure 12 on page 14) 320
FB
Peak current
limitation
I
shutdown current (See Figure 12 on page 14) 0.9 mA
FB
FB pin input
impedance
Current sense delay
to turn-OFF
= 0 V
V
FB
(See Figure 12 on page 14)
= 0 mA
I
D
(See Figure 12 on page 14)
I
= 0.2 A 200 ns
D
0.32 0.4 0.48 A
1.2 kΩ
tb Blanking time 500 ns
t
ONmin
Minimum Turn-ON
time
700 ns
Table 7. Overtemperature section
Symbol Parameter Test conditions Min Typ Max Unit
TSD
T
HYST
Thermal shutdown
temperature
Thermal shutdown
hysteresis
(See Figure 13 on page 14) 140 170 °C
(See Figure 13 on page 14) 40 °C
Table 8. Typical power capability
Mains type SO-8 DIP-8
European (195 - 265 Vac) 8W 13W
US / Wide range (85 - 265 Vac) 5W 8W
Doc ID 11977 Rev 2 5/21
Page 6
Pin connections and function VIPER12A-E
3 Pin connections and function
Figure 2. Pin connection
SOURCE
SOURCE
FB
VDD
1
2
3
4
8
7
6
5
DRAIN
DRAIN
DRAIN
DRAIN
SO-8 DIP-8
Figure 3. Current and voltage conventions
I
DD
I
FB
V
DD
V
FB
VDD DRAIN
FB
VIPer12A
CONTROL
SOURCE
SOURCE
SOURCE
FB
VDD
1
2
3
4
I
D
V
D
8
DRAIN
7
DRAIN
6
DRAIN
5
DRAIN
Table 9. Pin function
Pin Name Pin Function
Power supply of the control circuits. Also provides a charging current during start up
thanks to a high voltage current source connected to the drain. For this purpose, an
hysteresis comparator monitors the V
V
DD
SOURCE Power MOSFET source and circuit ground reference.
DRAIN
FB
6/21 Doc ID 11977 Rev 2
: Voltage value (typically 14.5 V) at which the device starts switching and turns
- V
DDon
off the start up current source.
: Voltage value (typically 8 V) at which the device stops switching and turns on
- V
DDoff
the start up current source.
Power MOSFET drain. Also used by the internal high voltage current source during
start up phase for charging the external VDD capacitor.
Feedback input. The useful voltage range extends from 0 V to 1 V, and defines the
peak drain MOSFET current. The current limitation, which corresponds to the
maximum drain current, is obtained for a FB pin shorted to the SOURCE pin.
voltage and provides two thresholds:
DD
Page 7
VIPER12A-E Rectangular U-I output characteristics
4 Rectangular U-I output characteristics
Figure 4. Rectangular U-I output characteristics for battery charger
A complete regulation scheme can achieve combined and accurate output characteristics.
Figure 4. presents a secondary feedback through an optocoupler driven by a TSM101. This
device offers two operational amplifiers and a voltage reference, thus allowing the regulation
of both output voltage and current. An integrated OR function performs the combination of
the two resulting error signals, leading to a dual voltage and current limitation, known as a
rectangular output characteristic. This type of power supply is especially useful for battery
chargers where the output is mainly used in current mode, in order to deliver a defined
charging rate. The accurate voltage regulation is also convenient for Li-ion batteries which
require both modes of operation.
Doc ID 11977 Rev 2 7/21
Page 8
Wide range of VDD voltage VIPER12A-E
5 Wide range of VDD voltage
The VDD pin voltage range extends from 9 V to 38 V. This feature offers a great flexibility in
design to achieve various behaviors. In Figure 4 on page 7 a forward configuration has been
chosen to supply the device with two benefits:
● As soon as the device starts switching, it immediately receives some energy from the
auxiliary winding. C5 can be therefore reduced and a small ceramic chip (100 nF) is
sufficient to insure the filtering function. The total start up time from the switch on of
input voltage to output voltage presence is dramatically decreased.
● The output current characteristic can be maintained even with very low or zero output
voltage. Since the TSM101 is also supplied in forward mode, it keeps the current
regulation up whatever the output voltage is.The V
the input voltage, that is to say with a ratio of about 4 for a wide range application.
pin voltage may vary as much as
DD
8/21 Doc ID 11977 Rev 2
Page 9
VIPER12A-E Feedback pin principle of operation
6 Feedback pin principle of operation
A feedback pin controls the operation of the device. Unlike conventional PWM control
circuits which use a voltage input (the inverted input of an operational amplifier), the FB pin
is sensitive to current. Figure 5. presents the internal current mode structure.
Figure 5. Internal current control structure
The power MOSFET delivers a sense current I
which is proportional to the main current Id.
s
R2 receives this current and the current coming from the FB pin. The voltage across R2 is
then compared to a fixed reference voltage of about 0.23 V. The MOSFET is switched off
when the following equation is reached:
R2ISIFB+()⋅ 0.23V=
By extracting I
Using the current sense ratio of the MOSFET G
:
S
I
GIDIS⋅ G
D
Doc ID 11977 Rev 2 9/21
0.23V
--------------- - IFB–=
I
S
R
2
:
ID
0.23V
⎛⎞
--------------- - IFB–
⋅==
ID
⎝⎠
R
2
Page 10
Feedback pin principle of operation VIPER12A-E
The current limitation is obtained with the FB pin shorted to ground (VFB = 0 V). This leads
to a negative current sourced by this pin, and expressed by:
FB
0.23V
--------------- -–=
R
1
I
By reporting this expression in the previous one, it is possible to obtain the drain current
limitation I
Dlim
:
1
1
I
Dlim
GID0.23V
⋅⋅=
⎛⎞
------ -
------ -+
⎝⎠
R
R
2
1
In a real application, the FB pin is driven with an optocoupler as shown on Figure 5 which
acts as a pull up. So, it is not possible to really short this pin to ground and the above drain
current value is not achievable. Nevertheless, the capacitor C is averaging the voltage on
the FB pin, and when the optocoupler is off (start up or short circuit), it can be assumed that
the corresponding voltage is very close to 0 V.
For low drain currents, the formula (1) is valid as long as IFB satisfies I
I
is an internal threshold of the VIPER12A. If IFB exceeds this threshold the device will
FBsd
stop switching. This is represented on Figure 12 on page 14, and I
FBsd
FB
< I
FBsd
, where
value is specified in
the PWM COMPARATOR SECTION. Actually, as soon as the drain current is about 12 % of
Idlim, that is to say 50 mA, the device will enter a burst mode operation by missing switching
cycles. This is especially important when the converter is lightly loaded.
Figure 6. I
It is then possible to build the total DC transfer function between I
transfer function
FB
and IFB as shown on
D
Figure 6 on page 10. This figure also takes into account the internal blanking time and its
associated minimum turn on time. This imposes a minimum drain current under which the
device is no more able to control it in a linear way. This drain current depends on the primary
inductance value of the transformer and the input voltage. Two cases may occur, depending
on the value of this current versus the fixed 50 mA value, as described above.
10/21 Doc ID 11977 Rev 2
Page 11
VIPER12A-E Startup sequence
7 Startup sequence
Figure 7. Startup sequence
This device includes a high voltage start up current source connected on the drain of the
device. As soon as a voltage is applied on the input of the converter, this start up current
source is activated as long as V
is lower than V
DD
. When reaching V
DDon
, the start up
DDon
current source is switched off and the device begins to operate by turning on and off its main
power MOSFET. As the FB pin does not receive any current from the optocoupler, the
device operates at full current capacity and the output voltage rises until reaching the
regulation point where the secondary loop begins to send a current in the optocoupler. At
this point, the converter enters a regulated operation where the FB pin receives the amount
of current needed to deliver the right power on secondary side.
This sequence is shown in Figure 7. Note that during the real starting phase t
consumes some energy from the V
capacitor, waiting for the auxiliary winding to provide a
DD
, the device
ss
continuous supply. If the value of this capacitor is too low, the start up phase is terminated
before receiving any energy from the auxiliary winding and the converter never starts up.
This is illustrated also in the same figure in dashed lines.
Doc ID 11977 Rev 2 11/21
Page 12
Overvoltage threshold VIPER12A-E
8 Overvoltage threshold
An overvoltage detector on the VDD pin allows the VIPER12A to reset itself when VDD
exceeds V
overvoltage event. Note that this event is only latched for the time needed by V
V
, and then the device resumes normal operation automatically.
DDoff
Figure 8. Overvoltage sequence
. This is illustrated in Figure 8., which shows the whole sequence of an
DDovp
V
DD
V
DDovp
V
DDon
V
DDoff
t
to reach
DD
V
DS
t
12/21 Doc ID 11977 Rev 2
Page 13
VIPER12A-E Operation pictures
9 Operation pictures
Figure 9. Rise and fall time
Figure 10. Start-up V
I
DD
I
DD0
V
DDhyst
V
DDoff
I
DDch
DD
current
V
DDon
Figure 11. Restart duty-cycle
VDS = 100 V
= 0 kHz
F
sw
V
DD
Doc ID 11977 Rev 2 13/21
Page 14
Operation pictures VIPER12A-E
Figure 12. Peak drain current vs feedback current
Figure 13. Thermal shutdown
14/21 Doc ID 11977 Rev 2
Page 15
VIPER12A-E Operation pictures
Figure 14. Switching frequency vs temperature
Figure 15. Current limitation vs temperature
Doc ID 11977 Rev 2 15/21
Page 16
Package mechanical data VIPER12A-E
10 Package mechanical data
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK
specifications, grade definitions and product status are available at: www.st.com. ECOPACK
is an ST trademark.
®
packages, depending on their level of environmental compliance. ECOPACK®
16/21 Doc ID 11977 Rev 2
Page 17
VIPER12A-E Package mechanical data
Table 10. DIP8 mechanical data
Databook (mm)
Ref.
Min. Nom. Max.
A 5.33
A1 0.38
A2 2.92 3.30 4.95
b 0.36 0.46 0.56
b2 1.14 1.52 1.78
c 0.20 0.25 0.36
D 9.02 9.27 10.16
E 7.62 7.87 8.26
E1 6.10 6.35 7.11
e2.54
eA 7.62
eB 10.92
L 2.92 3.30 3.81
Package Weight Gr. 470
Figure 16. Package dimensions
Doc ID 11977 Rev 2 17/21
Page 18
Package mechanical data VIPER12A-E
Table 11. SO8 mechanical data
Databook (mm)
Dim.
Nom Min Max
A 1.35 1.75
A1 0.10 0.25
A2 1.10 1.65
B 0.33 0.51
C 0.19 0.25
D 4.80 5.00
E 3.80 4.00
e 1.27
H 5.80 6.20
h 0.25 0.50
L 0.40 1.27
k 8° (max.)
ddd 0.1
Figure 17. Package dimensions
18/21 Doc ID 11977 Rev 2
Page 19
VIPER12A-E Order codes
11 Order codes
Table 12. Order codes
Order codes Package Packaging
VIPER12ASTR-E SO-8 Tape and reel
VIPER12AS-E SO-8 Tube
VIPER12ADIP-E DIP-8 Tube
Doc ID 11977 Rev 2 19/21
Page 20
Revision history VIPER12A-E
12 Revision history
Table 13. Document revision history
Date Revision Changes
09-Jan-2006 1 Initial release.
13-Dec-2010 2
Updated Table 3 on page 4, Table 4 on page 4 and Figure 10
on page 13.
20/21 Doc ID 11977 Rev 2
Page 21
VIPER12A-E
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Doc ID 11977 Rev 2 21/21
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