PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
C
URRENT
-M
ODE
PWM C
ONTROLLER
P
R O D U C T I O N
D
A T A
S
H E E T
T Y P I C A L A P P L I C AT I O N C I R C U I T S
V
CC
V
IN
(continued)
8 (14)
7 (12)
8 (14)
7 (11)
4 (7)
2 (3)
Q1
R
A
6
8
4
SG1842/43
R
B
2
1
5 (9)
To other
SGX842/43
555
TIMER
3
4 (7)
SG1842/43
6 (10)
5 (8)
I
1N4148
1 (1)
R
2
MPSA63
R
1
5 (9)
3 (5)
V
CS
R
S
C
V
CS
R
1
Where: V
CS
= 1.67
and V
C.S.MAX
= 1V (Typ.)
I
PK
=
R
S
R
1
+R
2
V - 1.3
R
1
R
2
t
SOFTSTART
= -ln
1 -
EAO
R
R +R
C
5
1
1
2
f=
f=
1.44
(R
A
+ 2R
B
)C
R
B
R
A
+ 2R
B
R
1
+R
2
where; V
EAO
≡
voltage at the Error Amp Output under
minimum line and maximum load conditions.
FIGURE 19.
— ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL
WITH SOFTSTART
Softstart and adjustable peak current can be done with the external
circuitry shown above.
FIGURE 20.
— EXTERNAL DUTY CYCLE CLAMP AND
MULTI-UNIT SYNCHRONIZATION
Precision duty cycle limiting as well as synchronizing several 1842/
1843's is possible with the above circuitry.
2.8V
1.1V
5V
8 (14)
R
T
2.5V
SG1842/43
0.5mA
4 (7)
C
T
SG1842/43
2 (3)
R
i
R
F
1 (1)
R
F
³
10K
Discharge
Current
I
d
= 8.2mA
FIGURE 21.
— OSCILLATOR CONNECTION
The oscillator is programmed by the values selected for the timing
components R
T
and C
T
. Refer to application information for
calculation of the component values.
FIGURE 22.
— ERROR AMPLIFIER CONNECTION
Error amplifier is capable of sourcing and sinking current up to 0.5mA.
12
Copyright © 2000
Rev. 1.6a
10/04
MICROSEMI [ MICROSEMI CORPORATION ]
