SG1844 查看數據表（PDF） - Microsemi Corporation
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SG1844 Datasheet PDF : 12 Pages
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PRODUCT DATABOOK 1996/1997
SG1844/SG1845 Series
CURRENT-MODE PWM CONTROLLER
PRODUCTION DATA SHEET
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 (continued)
VCC
VIN
7 (12)
8 (14)
4 (7)
7 (11)
Q1
2 (3)
SG1844/45
6 (10)
1 (1)
R2
2N2907
C
R1
5 (8)
3 (5)
5 (9)
RS
IPK =
V1
RS
Where: 0 ≤ V1 ≤ 1.0V
1.43 - 0.23 R1
and V1 =
R2
R
1+
1
R2
tSOFTSTART = -ln 1 -
VC
V
2
C
R1 R2
R +R
12
where: V2 =
0.5
R
1+ 1
R2
FIGURE 18. — ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL
WITH SOFTSTART
Softstart and adjustable peak current can be done with the external
circuitry shown above.
RA
6
RB
8
4
555
TIMER
2
C
1
f=
1.44
(RA + 2RB)C
f= R
RB
+ 2R
A
B
8 (14)
SG1844/45
3
4 (7)
To other
SG1844/45
5 (9)
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
SG1844/45
5V
7 (11)
RT
6 (10)
CT
Discharge
Current
Id = 8.2mA
2.5V
SG1844/45
2 (3)
Ri
1 (1)
RF
RF ³ 10K
0.5mA
FIGURE 20. — OSCILLATOR CONNECTION
The oscillator is programmed by the values selected for the timing
components RT and CT. 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
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