SG28424N MICROSEMI [Microsemi Corporation], SG28424N Datasheet - Page 12

• Manufacturer Part Number: SG28424N
• Description: CURRENT MODE PWM CONTROLLER
• Manufacturer: MICROSEMI [Microsemi Corporation]

12
SG1844/SG1845 Series
Softstart and adjustable peak current can be done with the external
circuitry shown above.
The oscillator is programmed by the values selected for the timing
components R
calculation of the component values.
FIGURE 18. — ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL
I
PK
C
=
and V
V
R
1
S
1
R
R
Where: 0 ≤ V
=
2
1
FIGURE 20. — OSCILLATOR CONNECTION
T
SG1844/45
2N2907
and C
1.43 - 0.23
Discharge
8 (14)
Current
4 (7)
2 (3)
1 (1)
1+
T
. Refer to application information for
2.8V
1.1V
R
R
1
2
1
WITH SOFTSTART
≤ 1.0V
SG1844/45
R
R
1
2
I
d
= 8.2mA
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
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
5 (9)
t
SOFTSTART
5V
7 (12)
where: V
C
7 (11)
6 (10)
U R R E N T
P
= -ln 1 -
R O D U C T I O N
7 (11)
6 (10)
5 (8)
3 (5)
V
2
CC
=
R



C
T
T
V
V
1+
- M
C
2
0.5
V



R
R
IN
C
1
2
Q1
R
O D E
S
R
R
1
1
+R
R
2
2
P W M C
D
Precision duty cycle limiting for a duty cycle of <50%, as well as
synchronizing several 1844/45's is possible with the above circuitry.
Error amplifier is capable of sourcing and sinking current up to 0.5mA.
A T A
O N T R O L L E R
C
f =
f =
FIGURE 19. — EXTERNAL DUTY CYCLE CLAMP AND
R
S
FIGURE 21. — ERROR AMPLIFIER CONNECTION
i
R
(R
H E E T
R
R
A
A
B
R
A
+ 2R
R
F
1.44
+ 2R
B
³ 10K
6
2
R
MULTI-UNIT SYNCHRONIZATION
F
B
B
(continued)
)C
2 (3)
1 (1)
8
TIMER
555
2.5V
4
1
SG1844/45
3
SG1844/45
To other
8 (14)
4 (7)
SG1844/45
0.5mA
Copyright © 2000
Rev. 1.6c
5 (9)