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PDF AN8091 Data sheet ( Hoja de datos )
| Número de pieza | AN8091 | |
| Descripción | Overvoltage Protective Circuit Incorporated Switching Power Supply | |
| Fabricantes | Panasonic Semiconductor | |
| Logotipo |  |
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AN8091, AN8091S
Overvoltage Protective Circuit Incorporated Switching Power Supply
s Overview
The AN8091 and AN8091S are equipped with various pro-
tection functions such as from overcurrent and overvoltage,
which can raise the reliability of the power supply, realizing the
high-speed control up to 500kHz.
s Features
• The PWM control frequency of up to 500kHz and miniatur-
ization realized.
• The power MOS FET of large capacitance directly control-
lable
• Built-in overcurrent protective function for two systems of
positive side detection and negative one, and intermittent
operation function for protection when overcurrent condition
proceeds further
• ON/OFF function allowing the power supply to be started or
stopped by the external signal, and current control function
required for the secondary side control incorporated
• Package : 16-lead DIP for the AN8091, 20-lead SOP for the
AN8091S
• Overvoltage protection circuit built-in
AN8091
Unit : mm
1 16
2 15
3 14
4 13
5 12
6 11
7 10
89
6.2±0.3
1.1±0.25
5.2±0.25 3.05±0.25
3—15˚ 7.62±0.25
0.30+–00.1.05
AN8091S
DIP016-P-0300D
Unit : mm
1 20
2 19
3 18
4 17
5 16
6 15
7 14
8 13
9 12
10 11
(0.4)
5.5±0.3
7.6±0.3
SOP020-P-0300C
1 page  
s Pin Descriptions
Pin No.
DIL SO
Symbol
Terminal description
11
VC Terminal applying the supply voltage to the output transistor.
22
VOUT Output terminal for IC. It drives the bipolar transistor.
3 3 VOUT-COM Ground terminal for the output transistor.
44
VF It detects the average level of output pulse and performs the timer control and duty control for the output.
5 7 ON/OFF IC turning ON/OFF terminal. “H” to stop the IC (output “L”), “L”to operate the IC.
68
OVP It detects the overvoltage to stop the IC. The stop condition is kept.
79
NC
8 10
F/B Terminal for current-feedback of power supply output.
9 11
10 12
11 13
12 14
13 17
14 18
15 19
TON
CF
TOFF
CT
GND
CLM–
CLM+
Terminal for connecting the resistor which determines the inclination of internally oscillated triangular wave during the charging period.
Terminal for connecting the capacitor which determines the frequency of internally oscillated triangular wave.
Terminal for connecting the resistor which determines the inclination of internally oscillated triangular wave during the discharging period.
Terminal for connecting the capacitor which determines the frequency of timer control.
Ground terminal for the signal system.
Overcurrent detection terminal for the negative potential side.
Overcurrent detection terminal for the positive potential side.
16 20
VCC Terminal applying the supply voltage. It detects the start voltage and stop one.
5 FIN (GND) Terminal which is directly connected with the IC chip. It has double function as radiator and ground terminal.
6 FIN (GND) Terminal which is directly connected with the IC chip. It has double function as radiator and ground terminal.
15 FIN (GND) Terminal which is directly connected with the IC chip. It has double function as radiator and ground terminal.
16 FIN (GND) Terminal which is directly connected with the IC chip. It has double function as radiator and ground terminal.
s Timing Chart
Under normal operation
Feedback voltage
from VIN or IIN
OSC oscillation
waveform
4.4V
1.8V
PWM output
waveform
0V
Internal clock
waveform
VOUT output
waveform
0V
VCC
0V
5 Page 
Either of the CLM+ terminal and the CLM– terminal has
flowing-out current of about 100 to 200µA. Fix the R1 to
100Ω. Compensation is required to cover the height of irreg-
ular element of C and R2.
Non-transparent conductive resistor should be used for R1,
R2 and detection resistance R.
Irregular element covered with time constant
[Fig.3–3]
5.4 Overcurrent Cycle Control Function Block (VF Control
Function)
As described in 5.3, the higher the frequency becomes, the
more the overcurrent protection suffers from decrease of con-
trol range due to response delay. It means :
1. Delay produced by the time constant of filter for pre-
venting the noise malfunction of the overcurrent detec-
tion block.
2. Delay of control IC itself
3. Turning off time of the switching device
By the above factors, the ON-period which is minimum-
controllable is limited to approx. 0.2 to 0.15µs, producing the
areas where control can not be achieved (Refer to Fig.4-1).
Limitation
0A
Minimum ON-width
Out of control
[Fig.4–1] Primary Side Current Waveform
In order to remove the above problem, the AN8091/S
incorporates the function which makes the oscillation fre-
quency variable for extension, corresponding the overcurrent
condition. The following shows why the above function can
realize the extension of control range :
Limitation
0A
T
TON
Frequency variable
D=
TON
T
(Time ratio)
0V
(DC)
0V
EIN
Filter
EOUT
[Fig.4–2] Primary Side Current Waveform
[Feed Forward] EO = DEIN
[Flyback]
EO =
D
1– D
EIN
(D=TON/T ; Time ratio)
(4–1)
The above represents the input and output generally (Refer to
Fig.4-3). The above relationship can be kept even under the
overcurrent dropping condition.
Overcurrent start
(VF=4V)
Dropping voltage
Intermittent operation start
(VF=3V)
Output Current (A)
[Fig.4 –3] Power Supply Output Dropping Curve
Therefore, when the output voltage reaches 0V under over-
current condition, time ratio D should be decreased toward 0.
However, since ON period TON has minimum limitation as
described in the above, time ratio D is decreased toward 0 by
extending the oscillation frequency T, attempting to satisfy
(4-1).
This overcurrent cycle control function works by the output
voltage level which is monitored by the VF terminal. The VF
terminal detects the dropping voltage under the overcurrent
condition of power supply output and performs the following
function switching according to its level :
1). 4V (typ.) < VF terminal voltage
Overcurrent protection function
2). 3V (typ.) < VF terminal voltage < 4V (typ.)
Overcurrent cycle control function (VF control)
3). VF terminal voltage < 3V (typ.)
Overcurrent cycle control function (VF control)
Intermittent operation function (timer control)
When the overcurrent is detected (CLM+ side or CLM–
side), if the VF terminal voltage decreases under 4V (typ.), as
described in Item 2-2 TOFF terminal voltage keeps the follow-
ing relationship :
VF = VTOFF + VF (offset)
(4–2)
Therefore, the TOFF period is extended, corresponding to
decrease of VF terminal voltage (Refer to Fig.2-5). This proc-
ess is shown in Fig.4-4.
Then, the description shifts to VF terminal setting.
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet AN8091.PDF ] | |
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