VIPER22AS-E STMicroelectronics, VIPER22AS-E Datasheet - Page 9

• Manufacturer Part Number: VIPER22AS-E
• Description: IC OFFLINE SWIT PWM SMPS 8SOIC
• Manufacturer: STMicroelectronics
• Series: VIPER™r

Specifications of VIPER22AS-E

• Output Isolation: Isolated
• Frequency Range: 54 ~ 66kHz
• Voltage - Input: 8 ~ 50 V
• Voltage - Output: 730V
• Power (watts): 7W
• Operating Temperature: 25°C ~ 125°C
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Output Power: 12 W, 7 W
• Input Voltage: 9 V to 38 V
• Switching Frequency: 60 KHz
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Output Voltage: 730V
• No. Of Outputs: 1
• Power Dissipation Pd: 7W
• Supply Voltage Range: 9V To 38V
• No. Of Pins: 8
• For Use With: 497-9049 - BOARD EVAL BASED VIPER22ASTR-E497-8215 - BOARD EVAL BASED ON VIPER22A497-5864 - EVAL BOARD DUAL OUTPUT VIPER22A497-5071 - EVAL BOARD DIMMABLE HB PWR LEDVIPER22-LED-EV - VIPER LED POWER SUPPLY
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6800-5; VIPER22AS-E

VIPer22ADIP/ VIPer22AS - E
By extracting I
Using the current sense ratio of the MOSFET G
The current limitation is obtained with the FB pin shorted to ground (V
a negative current sourced by this pin, and expressed by:
By reporting this expression in the previous one, it is possible to obtain the drain current
limitation I
In a real application, the FB pin is driven with an optocoupler as shown on
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 0V.
For low drain currents, the formula (1) is valid as long as IFB satisfies I
I
stop switching. This is represented on
PWM COMPARATOR SECTION. Actually, as soon as the drain current is about 12% of
Idlim, that is to say 85 mA, the device will enter a burst mode operation by missing switching
cycles. This is especially important when the converter is lightly loaded.
Figure 5.
It is then possible to build the total DC transfer function between I
Figure 5 on page 9
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 85mA value, as described above.
FBsd
is an internal threshold of the VIPer22A. If I
Dlim
I
FB
:
S
:
Transfer function
. This figure also takes into account the internal blanking time and its
t
-- ---- ----- ---- ----- ---- ----- ---- ---- --- -
t
-- ---- ----- ---- ----- ---- ----- ---- ---- --- -
ON m in
ON m in
L
L
85mA
⋅
⋅
V
V
1
2
I
I
IN
IN
D
Dpeak
I
0
Dlim
=
I
Dlim
G
I D
=
Rev1
I
Figure 11 on page 13
⋅
S
G
I
I
FB
S
I D
=
=
⋅
0.23V
--------------- - I
=
0.23V
R
G
–
2
I D
0.23V
--------------- -
ID
R
⋅
FB
–
⎛
:
1
⋅
0.23V
--------------- - I
⎛
FB
exceeds this threshold the device will
------ -
R
I
R
FBsd
1
Part
threshold
2
2
+
–
------ -
R
masked
1
, and I
1
FB
⎞
⎠
⎞
⎠
by
FBsd
D
the
and I
value is specified in the
FB
I
I
FBsd
FB
FB
= 0V). This leads to
FB
< I
Figure 4.
as shown on
FBsd
Operations
, where
which
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