SG2843M Microsemi Analog Mixed Signal Group, SG2843M Datasheet - Page 10
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SG2843M
Manufacturer Part Number
SG2843M
Description
IC PWM CURRENT MODE 8DIP
Manufacturer
Microsemi Analog Mixed Signal Group
Datasheet
1.SG3842M.pdf
(14 pages)
Specifications of SG2843M
Pwm Type
Current Mode
Number Of Outputs
1
Frequency - Max
500kHz
Duty Cycle
100%
Voltage - Supply
8.2 V ~ 30 V
Buck
No
Boost
No
Flyback
Yes
Inverting
No
Doubler
No
Divider
No
Cuk
No
Isolated
Yes
Operating Temperature
-25°C ~ 85°C
Package / Case
8-DIP
Frequency-max
500kHz
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
SG1842/SG1843 Series
10
OSCILLATOR
The oscillator of the 1842/43 family of PWM's is designed such
that many values of R
frequency, but only one combination will yield a specific duty
cycle at a given frequency.
Given: Frequency ≡ f
Calculate: R
For Duty-Cycles above 95% use:
Maximum Duty Cycle ≡ D
C
FIGURE 13 — OSCILLATOR TIMING CIRCUIT
T
T
= 267
=
F ≈
1.86 * D
R
f * R
GND
where .3 < D
R
1.86
T
(1.76)
V
/C
T
T
C
REF
(1.76)
T
T
and C
T
m
(1-D
where R
1/D
m
(µF)
)/D
T
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
m
m
will give the same oscillator
m
-1
m
- 1
< .95
T
C
≥ 5kΩ
U R R E N T
(Ω)
P
A P P L I C A T I O N I N F O R M A T I O N
R
C
R O D U C T I O N
T
T
- M
O D E
1000
P W M C
100
10
1
.001
D
C
formulas are less accurate for smaller duty cycles or higher
frequencies. This will require trimming of R
this error.)
Example:
cycle at a switching frequency of 50kHz. What are the values
of R
Given:
Calculate: R
FIGURE 14 — OSCILLATOR FREQUENCY vs. R
A T A
T
for a given frequency and maximum duty cycle. (Note: These
A set of formulas are given to determine the values of R
A Flyback power supply requires a maximum of 45% duty
T
and C
O N T R O L L E R
.002
f = 50kHz
D
S
m
C
T
?
H E E T
= 0.45
T
T
= 267
=
50000 * 674
1.86 * 0.45
.005
(1.76)
(1.76)
C
T
.55/.45
Value - (µF)
1/.045
= .025µF
.01
- 1
-1
= 674Ω
.02
T
FOR VARIOUS C
T
or C
T
to correct for
Copyright © 2000
.05
Rev. 1.6a 10/04
T
T
and
0.1