PRODUCT DATABOOK 1996/1997
SG1844/SG1845 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
SG1844/45
R
B
2
1
5 (9)
555
TIMER
3
4 (7)
SG1844/45
6 (10)
5 (8)
1N4148
1 (1)
R
2
2N2907
R
1
5 (9)
3 (5)
R
S
C
C
I
PK
=
V
1
Where: 0
≤
V
1
≤
1.0V
R
S
1.43 - 0.23
R
1
R
2
R
1+
R
1
2
V
C
R
1
R
2
t
SOFTSTART
= -ln 1
-
C
V
2
R
1
+R
2
where: V
2
=
0.5
1+
R
1
R
2
f=
f=
1.44
(R
A
+ 2R
B
)C
R
B
R
A
+ 2R
B
To other
SG1844/45
and V
1
=
FIGURE 18.
— ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL
WITH SOFTSTART
Softstart and adjustable peak current can be done with the external
circuitry shown above.
FIGURE 19.
— EXTERNAL DUTY CYCLE CLAMP AND
MULTI-UNIT SYNCHRONIZATION
Precision duty cycle limiting for a duty cycle of <50%, as well as
synchronizing several 1844/45's is possible with the above circuitry.
2.8V
1.1V
5V
7 (11)
2.5V
R
T
SG1844/45
0.5mA
6 (10)
C
T
SG1844/45
2 (3)
R
i
R
F
1 (1)
R
F
³
10K
Discharge
Current
I
d
= 8.2mA
FIGURE 20.
— 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 21.
— ERROR AMPLIFIER CONNECTION
Error amplifier is capable of sourcing and sinking current up to 0.5mA.
12
Copyright © 2000
Rev. 1.4 4/00
MICROSEMI [ MICROSEMI CORPORATION ]
