lx1554 Microsemi Corporation, lx1554 Datasheet - Page 16

• Manufacturer Part Number: lx1554
• Description: Ultra-low Start-up Current, Current-mode Pwm
• Manufacturer: Microsemi Corporation

LX1552/3/4/5
16
Soft start and adjustable peak current can be done with the external
circuitry shown above.
The RC low pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.
C
t
where; V
I
PK
SOFTSTART
FIGURE 32. — ADJUSTABLE BUFFERED REDUCTION OF CLAMP
minimum line and maximum load conditions.
=
FIGURE 30. — CURRENT SENSE SPIKE SUPPRESSION
V
R
R
R
CS
2
1
S
= -ln 1 -
EAO
LX155x
Where: V
MPSA63
voltage at the Error Amp Output under
7
8
4
2
1
5 (
V
LEVEL WITH SOFT-START
CS
EAO
6
5
3
= 1.67
R
- 1.3
1
R
+R
1
2
V
LX155x
CC
)
(
R
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
C
5
1
R
+R
(
1
U
DC BUS
2
R
Unless otherwise specified, pin numbers refer to 8-pin package.
R
1
LTRA
7
)
1
+R
R
T Y P I C A L A P P L I C A T I O N C I R C U I T S
and V
2
Q1
2
P
R
S
-L
)
R O D U C T I O N
C
OW
C.S.MAX
V
6
3
I
CC
PK(MAX)
S
= 1V (Typ.)
TART
=
1.0V
-U
R
V
I
S
PK
IN
P
Q
V
R
I
CS
PK
1
S
C
URRENT
D
A resistor (R
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.)
Precision duty cycle limiting as well as synchronizing several parts is
possible with the above circuitry.
, C
A T A
URRENT
FIGURE 33. — EXTERNAL DUTY CYCLE CLAMP AND MULTI-UNIT
f = (R
f = R
R
R
FIGURE 31. — MOSFET PARASITIC OSCILLATIONS
S
A
B
-M
1
) in series with the MOSFET gate reduces overshoot &
H E E T
A
ODE
A
+ 2R
R
1.44
+ 2R
B
7
6
2
0.01
PWM
LX155x
B
B
)C
7
5
8
5
TIMER
SYNCHRONIZATION
555
4
6
1
V
CC
R
1
LX155x devices
3
To other
DC BUS
Q1
R
S
8
4
LX155x
Copyright © 1994
5
Rev. 1.0a 1/01