LX1552 データシートの表示（PDF） - Microsemi Corporation
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LX1552 Datasheet PDF : 18 Pages
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PRODUCT DATABOOK 1996/1997
LX1552/3/4/5
ULTRA-LOW START-UP CURRENT, CURRENT-MODE PWM
PRODUCTION DATA SHEET
TYPICAL APPLICATION CIRCUITS
Unless otherwise specified, pin numbers refer to 8-pin package.
FIGURE 30. — CURRENT SENSE SPIKE SUPPRESSION
FIGURE 31. — MOSFET PARASITIC OSCILLATIONS
VCC
DC BUS
VCC
DC BUS
7
7
LX155x
6
5
3
Q1
IPK
C
RS
IPK(MAX) =
1.0V
RS
LX155x
R1
Q1
6
RS
5
The RC low pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.
FIGURE 32. — ADJUSTABLE BUFFERED REDUCTION OF CLAMP
LEVEL WITH SOFT-START
VCC
VIN
7
8
4
Q1
2
LX155x
6
IPK
1
R2
MPSA63
C
R1
VCS
3
RS
5
( ) IPK =
VCS
RS
Where: VCS = 1.67
R1
R1+R2
and VC.S.MAX = 1V (Typ.)
tSOFTSTART = -ln
1-
VEAO - 1.3
5 ( R1 )
R1+R2
( ) R1 R2
R1+R2
C
where; VEAO ≡ voltage at the Error Amp Output under
minimum line and maximum load conditions.
Soft start and adjustable peak current can be done with the external
circuitry shown above.
A resistor (R ) in series with the MOSFET gate reduces overshoot &
1
ringing caused by the MOSFET input capacitance and any inductance
in series with the gate drive. (Note: It is very important to have a low
inductance ground path to insure correct operation of the I.C. This
can be done by making the ground paths as short and as wide as
possible.)
FIGURE 33. — EXTERNAL DUTY CYCLE CLAMP AND MULTI-UNIT
SYNCHRONIZATION
8
RA
8
4
7
LX155x
RB
6
555
TIMER
3
4
2
5
1
0.01
5
f=
1.44
(RA + 2RB)C
f=
RB
RA + 2RB
To other
LX155x devices
Precision duty cycle limiting as well as synchronizing several parts is
possible with the above circuitry.
16
Copyright © 1994
Rev. 1.0a 1/01
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