STMICROELECTRONICS VIPER31SP

VIPer31SP
BATTERY CHARGER PRIMARY I.C.
ADVANCE DATA
T YPE
V DSS
In
R DS(on)
VIPer31SP
600 V
1 A
6.5 Ω
10
FEATURE
■
RECTANGULAR CHARACTERISTIC,
WITHOUT OPTOCOUPLER
■
INTERNALLY TRIMMED CURRENT
REFERENCE
■
FIXED SWITCHING FREQUENCY,
ADJUSTABLE UP TO 150 KHZ
■
AUXILIARY VOLTAGE REGULATOR
■
SOFT START AND SHUT DOWN CONTROL
■
AUTOMATIC BURST MODE OPERATION IN
STAND-BY CONDITION ABLE TO MEET
”BLUE ANGEL” NORM (<1W TOTAL POWER
CONSUMPTION)
■
UNDERVOLTAGE LOCK-OUT WITH
HYSTERESIS
■
INTEGRATED START UP SUPPLY
■
AVALANCHE RUGGED
■
OVERVOLTAGE PROTECTION
■
OVERTEMPERATURE PROTECTION
■
CYCLE BY CYCLE CURRENT LIMITATION
■
DEMAGNETISATION CONTROL
1
Power SO-10
DESCRIPTION
VIPer31SP combines on the same silicon chip a
PWM control dedicated to output current
regulation together with an optimised high voltage
avalanche rugged vertical power MOSFET
(600V/1A). Typical applications cover battery
chargers with constant current and constant
voltage output characteristics, without any
optocoupler between primary and secondary
sections. Typical output power capability is 15 W
in wide range condition and 30 W in single range
or with doubler configuration. Burst mode
operation is an additional feature of this device,
offering the possibility to operate in no load
condition with an input power as low as 1W. This
feature insures the compliance towards ”Blue
Angel” norm and other similar ones.
BLOCK DIAGRAM
FB
COMP
OSC
DRAIN
VCC
ON/OFF
OSCILLATOR
2.6 V
+
-
+
UVLO
LOGIC
R1
FF
+
R2
29 V
-
R3
Q
R4
PWM
LATCH
OVERTEMP.
DETECTOR
200 ns
BLANKING
-
-
1.5 A
+
10 V
REGULATOR
VDD
+
CURRENT
REGULATION
GND
CREF
CSENSE
DSENSE
SOURCE
SC12000
January 1998
1/16
VIPer31SP
ABSOLUTE MAXIMUM RATING
Symb ol
V DS
ID
I DREV
VCC
VX
IX
I DSENSE
V esd
I D(AV)
Parameter
o
Continuous Drain-Source Voltage (T j = 25 to 125 C)
Maximum DC Drain Current
Reverse DC Drain Current
Supply Voltage
Voltage Range Input (CSENSE, COMP, F B, OSC, CREF)
Current Input (CSENSE, CO MP, F B, O SC, CREF
Current Range Input (DSENSE)
Electrostatic Discharge (R = 1.5 KΩ C = 100pF)
Avalanche Drain-Source Current, Repetitive or Not-Repetitive
(T C = 100 o C, Pulse Width Limited by T J max)
Avalanche Drain-Source Energy, Repetitive or Not-Repetitive
(T C = 25 o C, Pulse Width Limited by TJ max)
Power Dissipation at T C = 25o C
Junction O perating Temperature
Storage Temperature
E D(AV)
P tot
Tj
T s tg
Value
600
Internally Limited
-2.5
0 to 35
-03 to V DD
10
-10 to +10
2000
T BD
Unit
V
A
A
V
V
mA
mA
V
A
T BD
mJ
62
-40 to 150
-65 to 150
W
C
o
C
o
THERMAL DATA
R t hj-ca se
Thermal Resistance Junction-case
R th j-a mb.
Max
Thermal Resistance Junction-ambient (Note1)
Max
2.0
o
C/W
50
o
C/W
Note 1 : This thermal resistance corresponds to the standard mounting on a FR4 type printed circuit board.
CURRENT AND VOLTAGE CONVENTIONS
IDSENSE
ICOMP
IFB
IDRAIN
ICC
3
6
IDD
8
1
DSENSE
-
VDD
2.6V
IOSC
2
9
COMP
FB
VCC
11
DRAIN
CURRENT
CONTROL
+
VOLTAGE CONTROL
OSC
GND
10
CREF
4
ICREF
CSENSE
7
SOURCE
5
ICSENSE
VIPer31
ISOURCE
VCOMP
VFB
VCC
VDD
VOSC
VCREF
VCSENSE
VSOURCE
VDRAIN VDSENSE
RS
SC12020
2/16
VIPer31SP
CONNECTION DIAGRAMS (top View)
PINS FUNCTIONAL DESCRIPTION
DRAIN PIN:
Integrated power MOSFET drain pin. It provides
internal bias current during start-up via an
integrated high voltage current source which is
switched off during normal operation. The device
is able to handle an unclamped current during its
normal operation, assuring self protection against
voltage surges, PCB stray inductance, and
allowing a snubberless operation for low output
power.
SOURCE PIN:
Integrated power MOSFET source pin. To be
connected to an external current sense resistance
which defines the output current value.
GND
Used as the signal reference for all low level
signals. To be connected to the cold point of the
current sense resistance.
VDD PIN:
It corresponds to the low voltage supply of the
control part of the circuit. If Vdd goes below 6V,
the circuit is shut down and the start-up current
source is activated. The circuit resumes normal
operation when the VDD voltage reaches 8V. An
internal low drop linear regulator generates the
VDD voltage from the VCC one, thus limiting its
value at 10V.
VCC PIN:
This pin receives the auxiliary unregulated
voltage from the main transformer, which can
range from 7V up to 27V during normal operation.
It delivers a start up current of 1.5mA during the
shut down phase. The VCC pin is also connected
to an internal 10V low drop regulator which
provides the VDD voltage.
CSENSE PIN:
Receives the voltage of the current sense
resistor, representative from the power MOSFET
drain current.
CREF PIN:
Serves as a reference for the peak power
MOSFET drain current. It is also the output of the
curent regulation function, which adjusts this
reference voltage to keep the average output
current constant. To be connected to an external
filtering capacitor.
DSENSE PIN:
Detects the full demagnetisation of the main
transformer, in order to drive the current
regulation function. Refer to the application part
for further details. It is also used to prevent any
new turn on of the power MOSFET during the
demagnetisation phase.
FB PIN:
This is the inverting input of the voltage mode
error amplifier. This error amplifier is in charge of
the limitation of the VCC voltage when the output
current is lower than the nominal regulated one.
COMP PIN:
This is the output of the voltage mode error
amplifier. An external R-C network connected
between this pin and the FB pin defines the
bandwidth of the voltage regulation loop, and
insures the stability of the converter.
OSC PIN:
An RT-CT network must be connected on that pin
to define the switching frequency. Note that
despite the connection of RT to VDD, no
significant frequency change occurs for VDD
varying from 7V to 10V. It provides also a
synchronisation capability, when connected to an
external frequency source.
3/16
VIPer31SP
ELECTRICAL CHARACTERISTICS (TJ = 25 oC, VCC = 12 V, unless otherwise specified)
POWER SECTION
Symb ol
BV DSS
I DSS
Parameter
Drain-Source Voltage
Test Cond ition s
I D = 1 mA
VCOMP = 0 V
Min.
Typ .
Max.
600
Un it
V
Off-State Drain Current V DS = 500 V
V COMP = 0 V
Static Drain Source on
Resistance
I D = 0.3 A
o
T J = 25 C
o
T J = 100 C
V SENSE = 0 V
tf
Fall Time
ID = 0.3 A
(see fig. 1)
V in = 300 V (1)
250
ns
tr
Rise Time
I D = 0.3 A
(see fig. 1)
V in = 300 V (1)
TBD
ns
Output Capacitance
V DS = 25 V
TBD
pF
R DS( on)
C OSS
1
mA
6.5
10
Ω
Ω
(1) On Inductive Load, Clamped.
SUPPLY SECTION
Symb ol
Parameter
Test Cond ition s
I CCch
Start-up Charging
Current
V DD = 0 to V DDon
(see fig. 2)
I CC0
Operating Supply
Current
F SW = 0 KHz
(see fig. 2)
I CC1
Operating Supply
Current
I CC2
Min.
V DS = 250 V
Typ .
Max.
Un it
-1.5
mA
10
mA
F SW = 100 KHz
TBD
mA
Operating Supply
Current
F SW = 200 KHz
TBD
mA
V DDo ff
Undervoltage
Shutdown
(see fig. 2)
6
V
8
V
2
V
V DDo n
Undervoltage Reset
(see fig. 2)
VDDhyst
Hysteresis Start-up
(see fig. 2)
TBD
V DDreg
Output Voltage
(see fig. 2)
TBD
V DO
Drop O ut Voltage
V CC = 9 V
(see fig. 2)
I DDsc
Short Circuit Current
V DD = 0 V
IDD = T BD mA
T BD
V
T BD
mV
T BD
mA
OSCILLATOR SECTION
Symb ol
Parameter
Test Cond ition s
Min.
Typ .
Max.
Un it
F SW1
Oscillator Frequency
Initial Accuracy
R T = 8.2 KΩ
o
T J = 25 C
C T = 3300 pF
(see fig.3)
TBD
50
T BD
KHz
F SW2
Oscillator Frequency
Total Variation
C T = 3300 pF
R T = 8.2 KΩ
V DD = 7 to10 V
TBD
50
T BD
KHz
V OSC
HI
Oscillator Peak Voltage (1)
6.2
V
V OSC
LO
Oscillator Valley
Voltage
2.5
V
(1)
(1) The peak and valley voltages are used internally by the voltage mode PWM. The sawtooth generated by the oscillator is compared to
the COMP pin voltage to limit the duty cycle of the power mosfet switch. See block diagram on page 1.
4/16
VIPer31SP
ELECTRICAL CHARACTERISTICS (continued)
ERROR AMPLIFIER SECTION
Symb ol
V REF
Parameter
Reference Voltage
Test Cond ition s
I COMP = 0 mA
∆V REF
Temperaure Variation
GBW
Unity G ain Bandwidth
(see fig. 4)
A VOL
Open Loop Voltage
Gain
(see fig. 4)
I FB
Input Bias Current
V FB = 5 V
I COMP = -100 µA
V COMP
LO
Output Low Level
V COMP
HI
Output High Level
o
T J = 25 C
Min.
Typ .
Max.
Un it
TBD
2.6
T BD
V
TBD
T BD
%
TBD
400
KHz
50
dB
2.5
5
µA
V FB = 5 V
1
V
I COMP = 100 µA
VF B = 0 V
9
V
I COMP
LO
Output Low Current
Capability
V COMP = 5 V
V FB = 5 V
3.5
mA
ICOMP
HI
Output High Current
Capability
V COMP = 5 V
V FB = 0 V
-3.5
mA
CURRENT REGULATION SECTION
Symb ol
V REG
td
Parameter
Reference Voltage
(see fig. 5)
Current Sense Delay
to Turn-off
(See fig 1)
V DSENSEth Demagnetization
Detector Threshold
Voltage
V DSENSEcl
Test Cond ition s
Demagnetization
Detector Clamping
Voltage
Min.
Typ .
Max.
Un it
320
350
380
mV
350
ns
(see fig. 6)
I DSENSE = 10 mA
(see fig. 6)
2.6
V
6
V
PROTECTION SECTION
Symb ol
I Dl im
Parameter
Test Cond ition s
Peak Drain Current
Limitation
RS = 0
(see fig. 9)
Current Limitation
Blanking T ime
RS = 0
(see fig. 9)
V CClim
V CC Overvoltage
Threshold
V FB = 0 V
(see fig. 7)
VCChyst
V CC Overvoltage
Hysteresis
V FB = 0 V
(see fig. 7)
T SD
Thermal Shutdown
Temperature
(see fig. 8)
T SDhyst
Thermal Shutdown
Hysteresis
(see fig. 8)
tb
Min.
Typ .
1
Max.
Un it
2.5
A
µs
1.2
26
35
2
150
TBD
V
V
o
C
o
C
5/16
VIPer31SP
Figure 1: Switching Times
Figure 2: UVLO Logic Behaviour
ICC
Tr
VDS
ICC0
2.VIN
tf
VDDhyst
VIN
VDDoff
t
VCC
VDDon
ICCch
ID
VDD
VDDreg
td
VCREF
RS
VCC
t
VDDreg+VDO
SC12030
SC12040
Figure 3: Switching Frequency Setting
Oscillator frequency vs Rt and Ct
1,000
+
500
VDD
Frequency (kHz)
300
Ct = 1.5 nF
RT
200
OSC
Ct = 2.7 nF
0.62 VDD
+
S
Q
R
100
+
Ct = 4.7 nF
CT
500
0.25 VDD
50
Ct = 10 nF
30
GND
20
1
2
3
5
10
20
30
50
Rt (kΩ)
SC12050
6/16
VIPer31SP
Figure 4: Error Amplifier Phase and Gain
(dB)
100
(°)
200
150
PHASE
50
100
GAIN
50
0
0
-50
Cload = 100pF
-50
-100
1
10
100
1k
10k
100k
-150
10M
1M
Frequency (Hz)
SC12060
Figure 5: Reference Voltage Measurement
3
6
8
FB
VCC
2
11
DRAIN
CURRENT
CONTROL
+
2.6V
VOLTAGE CONTROL
OSC
VIPer31
12V
1
DSENSE
-
VDD
8.2kΩ
4.7uF
16V
9
COMP
GND
10
CREF
CSENSE
SOURCE
4
7
5
3.3nF
Vreg
SC12070
7/16
VIPer31SP
Figure 6: Demagnetisation Control Logic
DRAIN
VDD
VAUX
FROM
PWM
LATCH
10µA
DSENSE
+
VAUX
VDSENSEth
VCC
S Q
VDSENSEth
t
EOD
R
VDSENSEcl
AUXILIARY
WINDING
Q
RD
1
EOD
1
GND
SOURCE
t
0
SC12080
Figure 7: Overvoltage Protection
Figure 8: Overtemperature Protection
Tj
Tsd
VCC
Tsdhyst
VC Clim
VCChyst
t
ID
t
VCREF
t
VDD
VDDon
t
VDDoff
ID
t
VCREF
t
t
SC12090
SC12100
8/16
VIPer31SP
Figure 9: Blanking Time and Current Limitation
ID
Figure 11: Typical Output Characteristics
tb
Iout vs Uout curves for Vin = 100, 200, 300, 400 VDC, Ta = 25°C
1
Constant voltage
operation (+/-7%)
Iout
(A)
IDlim
0.8
Constant current
operation (+/-2.5%)
0.6
t
0.4
ID
Short circuit or
Low voltage
operation
0.2
IDlim
0
5
10
15
Uout
(V)
SC12120
t
SC12110
Figure 10: Typical AC/DC Adapter
F1
L
T1
FUSE
BR1
-
C1
100nF
R1
D1
+
IOUT
STPS1100U
1A/600V
C2
10uF
400V
N
C3
330uF
25V
T2
GND
CTN
D2
R2
1N4148
22
R4
22k
R3
27k
R6
C5
10k
2.2n
3
6
8
VCC
C7
10uF
35V
1nF
1
DSENSE
-
VDD
R8
8.2k
2
9
COMP
FB
2.6V
R5
680k
C4
11
DRAIN
R7
680k
CURRENT
CONTROL
+
C6
2.2nF
VOLTAGE CONTROL
OSC
GND
10
CREF
4
CSENSE
7
SOURCE
5
U1
VIPer31
C8
4.7uF
16V
R9
470
R10
2.7k
C9
2.7nF
C10
470nF
R11
1.3
SC12130
9/16
VIPer31SP
topology cannot be easily kept constant, as it
depends on the output voltage. Actually, if the
peak primary current is fixed, the converter
behaves as a constant power generator.
Therefore, a modulation of the peak primary
current versus output voltage must be done in
order to get the constant output current
characteristic. A conventional way consists to use
an optocoupler between primary and secondary,
with additional circuitry on secondary side
(Reference, error amplifier and current sense
resistor).
This device avoids the use of all the secondary
circuitry by controlling from primary side the
secondary average output current. Figure 12
presents the internal constitution of the current
control function. It is built around a constant
current source Iref, and a mosfet switch driven
with the complemented signal EOD, in series with
a resistance R. The middle point of these
elements is available on the CREF pin.
The EOD signal is generated by the
demagnetisation function, which is monitoring the
voltage of the main transformer auxiliary winding.
OPERATION DESCRIPTION :
This device is intended to be used in off line
AC/DC adapter where the desired output
characteristic must present a rectangular
characteristic. For output voltage values lower
than a fixed value, the average output current
must be constant, whatever are the input or
output voltages. If the output current consumed
by the load is lower than the previous constant
current value, the output voltage value must be
limited. In addition, the device provides protection
against output short circuits and overtemperature
events.
The two modes of operation are described in the
following paragraphs. Figure 10 presents a typical
application of which the output characteristic can
be seen on figure 11.
CONSTANT OUTPUT CURRENT
The power topology to be used with this device is
a simple discontinuous flyback, as shown on
figure 10. The average output current of such a
Figure 12: Constant Current Operation
+Vin
D1
n
IOUT
Is
C1
GND
D2
Ip
Tsw
VCREF
Ip
R1
RS
T
VCC
DSENSE
t
DRAIN
Is
Demag.
Iref
Oscillator
n. VCREF
RS
EOD
R
C2
t
PWM
Latch
Q
EOD
R
1
+
GND CS ENSE VIPer31 SOURCE
CREF
t
0
Ic
Iref
Ic
Uc
tonsec
R2
t
RS
C
Iref -
Uc
R
SC12140
10/16
VIPer31SP
An external resistance R1 is needed to withstand
the negative voltage generated by the winding. As
long as the transformer is delivering some energy
on secondary side, the negated EOD signal
remains in the high state and the mosfet switch Q
is on. The duration of this state is noted tonsec
and corresponds to the time where the secondary
current is flowing through D1. For details about
the demagnetisation function, refer to figure 6.
The average output current can be expressed as:
IOUT =
IS
tONSEC
X
2
TSW
(1)
Where :
IS is the peak secondary current.
tONSEC is the conduction time on secondary side.
TSW is the switching period.
Taking into account the transformer ratio n
between primary and secondaryside, IS can also
be expressed versus primary peak current IP :
IS = n x IP
(2)
The value of the capacitor C is sufficiently high to
consider the voltage Uc as constant. This
capacitor is submitted to a charging current and
discharging current at the rhythm of the switching
frequency. As these currents are in the range of a
few mA (Iref is typically 1 mA), a 470 nF is a
suited value for a switching frequency of 60 kHz.
In steady state, it can be written that the charge is
equal to the discharge :
UC
IREF x (TSW − t ONSEC) = (
− IREF ) x t ONSEC
R
It comes :
TSW
UC = R x IREF x
(3)
tONSEC
As UC can be considered as a constant voltage,
can be also expressed as :
UC
IP =
(4)
RS
Combining (1), (2), (3) and (4) :
R x IREF
n
IOUT =
x
2
RS
This last expression shows that the average
output current doesn’t depend any more neither
on the output voltage, nor on the duty cycle, nor
on the input voltage. The only parameters which
are setting its value are :
The transformer ratio n.
The sense resistor value RS
The product R x IREF
This product corresponds to a voltage which is
noted Vreg in the specification tables. Figure 5
shows the test fixture for measuring it : The
DSENSE pin is held in the high state (In fact, it is
left open, as an internal pull up current source is
internally connected on this pin) and the mosfet
switch Q is always in the high state. In this case,
the voltage on the CREF pin establishes at
R x IREF .
Note that the oscillator must be running for the
demagnetisation block to sample correctly the
DSENSE pin.
As Vreg has a typical value of 350 mV, the output
current can be finally written as :
0.175
IOUT = n x
RS
A sense resistor of 1.3 Ω with a transformer ratio
of 6 gives a typical output current of about 800
mA.
The schematics of figure 10 shows a
compensation on the CSENSE pin with the two
resistances R5 and R7. These resistances are
connected on the Vin input voltage and are
providing an offset on the current sense pin. The
higher is the input voltage, and the higher is this
offset current. The purpose of this compensation
is to cancel the effect of the current control
propagation time td, which induces an extra
current on top of the theoretical peak current Ip
given by (4).
The output current obtained with this
compensation can be seen on figure 11. The
typical ”flatness” is about +/-2.5 %, including the
input voltage variation from 100 VDC to 400 VDC.
If less accuracy is needed, these two resistances
can be omitted.
CONSTANT VOLTAGE OPERATION
An another part of the circuit is in charge of the
regulation of the output voltage, and generates
the vertical characteristic of figure 11. It consists
of a primary feedback regulation, with a
conventional voltage mode control : An
operational amplifier with an internal voltage
reference of 2.6 V is configured in error amplifier
and defines the duty cycle of the power mosfet
switch by comparison with the oscillator sawtooth
(See block diagram on page 1).
As it is a primary feedback, the accuracy of the
output voltage depends closely on the
transformer coupling quality. This is especially
11/16
VIPer31SP
true for low output current where the output
voltage can reach high values, as shown on
figure 11 : 20 V can be reached for a nominal
regulated one of 14.5 V, with a typical
transformer. But a simple clamping zener can
limit it to about 17 V with a reasonable dissipated
power. The 10 % to 100 % output load regulation
is better than +/-7 %.
COMPONENTS SIZING
The following procedure defines the value of
essential parameters for the transformer and the
sensing resistance in a typical application. The
user can adapt by himself the final design,
according to specific needs, if any.
- 1. Define the maximum output voltage
MAX
for which the converter has still to
OUT
operate in constant current mode.
V
- 2. Check that the ratio between the minimum
MIN
MAX
and V
is
OUT
OUT
lower than 2.5. This ratio is limited by the
overvoltage protection value (Typically 29 V)
and VDDreg (Typically 10 V) and their
tolerances.
operating output voltage V
- 3. Compute the transformer turn ratio n from
primary to secondary with the formula :
np
100
n=
=
MAX ns
V
OUT
- 4. Compute the sense resistance value with the
formula :
RS = n x
0.175
IOUT
- 5. Compute the transformer turn ratio nAUX
from auxiliary to secondary with the formula :
na
25
nAUX =
=
MAX ns
V
OUT
- 6. The current control function requires the
converter to work in discontinuous mode. The
primary inductance value LP of the transformer
can be computed by respecting this constraint
in all conditions, or by using the following
MIN
V
x TSW
n
IN
formula : LP =
x
where :
10
IOUT
MIN
V
is the minimum input rectified DC voltage
IN
from the mains.
12/16
TSW is the switching period.
START UP SEQUENCE
An integrated high voltage current source
provides a bias current from the DRAIN pin during
the start-up phase. This current is partially
absorbed by internal control circuits which are
placed into a standby mode with reduced
consumption and also provided to the external
capacitors connected to the VDD and VCC pins. As
soon as the voltage on this pin reaches the high
voltage threshold VDDon of the UVLO logic, the
device turns into active mode and starts
switching. The start up current generator is
switched off, and the converter should normally
provide the needed current on the VDD pin
through the auxiliary winding of the transformer,
as shown on figure 13.
The sum of the external capacitors CSTART on the
VDD and VCC pins must be sized according to the
time needed by the converter to start up, when
the device starts switching. This time tSS depends
on many parameters, among which transformer
design, output capacitors, capacitor value
implemented on the CREF pin (See soft start
consideration here after). The following formula
can be used for defining the minimum capacitor
needed :
IDD x tSS
CSTART >
where :
VDDhyst
IDD is the consumption current on the VDD pin
when switching. Refer to specified IDD1 and IDD2
values.
tSS is the start up time of the converter when the
device begins to switch. Worst case is generally
at full load.
VDDhyst is the voltage hysteresis of the UVLO
logic. Refer to the minimum specified value.
CSTART = CVDD + CVCC is the sum of both
capacitors on VDD and VCC pins. Once is defined,
allot a standard 4.7 µF / 16 V on the VDD pin, and
the rest on the VCC pin. The VDD capacitor
insures a correct decoupling of the internal serial
regulator between VCC and VDD.
Soft start feature is implemented through the
CREF capacitor which is also filtering the CREF
voltage. The minimum value of this capacitor has
to be set according to the switching frequency, in
order to filter the charging and discharging current
issued from the CREF pin (Refer to the current
control description part). It can be increased from
VIPer31SP
Figure 13: Start Up Circuit and Sequence
2 mA
DRAIN
VCC
LDO
Reg.
AUXILIARY
WINDING
CVCC
CVDD
VCC
ON/OFF
UVLO LOGIC
+
Ref
VDD
(V)
VIPer31
GND
VDDreg
VDDon
VDD
VDDoff
tss
SOURCE
t
SC12150
this value to provide a soft start feature, of which
the duration depends on some circuit parameters,
like transformer ratio, sense resistor, output
capacitors and load. The user will define the best
appropriate value by experiments.
SHORT CIRCUIT OPERATION
In case of abnormal condition where the auxiliary
winding is unable to provide the low voltage
supply current to the VCC pin (i.e. short circuit on
the output of the converter), the external
capacitors discharge themselves down to the low
threshold voltage VDDoff of the UVLO logic, and
the device get back to the inactive state where the
internal circuits are in standby mode and the start
up current source is activated. The converter
enters a endless start up cycle, with a start-up
duty cycle defined by the ratio of charging current
towards discharging when the VIPer31 tries to
start. This ratio is fixed by design to 1.5 to 12,
which gives a 11% start up duty cycle, while the
power dissipation at start up is approximately 0.6
W, for a 230 Vrms input voltage.
The average output short circuit current is the
product of the start up duty cycle by the output
current flowing during the active phase of the
device (See figure 14). This output current is
limited by either the CREF pin voltage, or the
internal current limitation of 1.3 A. These values
together with the low value of start-up duty cycle
prevents the stress of the output rectifiers and of
the transformer when in short circuit.
Figure 14 : Short circuit operation
VDD
VDDon
VDDoff
t
Iout
Isc
Average
output current
t
SC12160
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VIPer31SP
OVERVOLTAGE PROTECTION
If the output voltage accuracy is not a concern,
but only a limitation is desired, the internal
overvoltage protection can be used. In this case,
five components can be taken out from the
schematics of figure 10 (R3-R10-R6-C4-C5) and
the input pin FB of the error amplifier is simply
grounded. The internal overvoltage protection will
act as soon as the VCC voltage reaches typically
29 V, by turning off the power mosfet switch. An
hysteresis of about 3 V will enable again the
switching of the device at a lower voltage level on
the VCC pin. This results in an efficient voltage
limitation, in a burst mode operation type, with
some ripple on the output. Case by case
experiments will define the correct value of output
capacitor C3, according to the loading current in
low output power condition.
STANDBY MODE
The standby mode is represented by a very low
output current, corresponding to a full loaded
battery in a battery charger application. The
output voltage is limited by either the overvoltage
14/16
protection or the error amplifier, according to the
design. This results into different situations :
- In case the overvoltage protection is used, the
burst mode operation as described previously
takes place, governed by the hysteresis of the
overvoltage comparator.
- If the error amplifier is used, many situation can
occur, depending on the compensation network
foreseen by the designer. These situations can
range from a normal continuous operation, to
burst mode. In any case, the output voltage will
be regulated to the desired value.
Note that the burst operation is providing a very
low input power consumption, because it reduces
the switching frequency, and thus commutation
losses. Less than 1 W of input power can be
observed in this operative mode, with a few
hundreds of mW delivered to the secondary load.
This is far compliant with standby standards, like
the ”Blue Angel” one.
VIPer31SP
Power SO-10 MECHANICAL DATA
mm
DIM.
MIN.
inch
TYP.
MAX.
MIN.
TYP.
MAX.
A
3.35
3.65
0.132
0.144
A1
0.00
0.10
0.000
0.004
B
0.40
0.60
0.016
0.024
c
0.35
0.55
0.013
0.022
D
9.40
9.60
0.370
0.378
D1
7.40
7.60
0.291
0.300
E
9.30
9.50
0.366
0.374
E1
7.20
7.40
0.283
0.291
E2
7.20
7.60
0.283
0.300
E3
6.10
6.35
0.240
0.250
E4
5.90
6.10
0.232
e
1.27
0.240
0.050
F
1.25
1.35
0.049
0.053
H
13.80
14.40
0.543
0.567
1.80
0.047
h
0.50
L
0.002
1.20
q
1.70
0.067
o
α
0.071
8o
0
B
0.10 A B
10
5
e
0.25
B
=
=
=
E4
=
=
=
1
E1
=
E3
=
E2
=
E
=
=
=
H
6
SEATING
PLANE
DETAIL ”A”
A
C
M
Q
h
D
= D1 =
=
=
SEATING
PLANE
A
F
A1
A1
L
DETAIL ”A”
α
0068039-C
15/16
VIPer31SP
Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsability for the
consequences of use of such information nor for any infringement of patents or other rights of third parties which may results from its use. No
license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications mentioned
in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.
SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express
written approval of SGS-THOMSON Microelectonics.
 1998 SGS-THOMSON Microelectronics - Printed in Italy - All Rights Reserved
SGS-THOMSON Microelectronics GROUP OF COMPANIES
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