SG3843D MICROSEMI [Microsemi Corporation], SG3843D Datasheet - Page 11

• Manufacturer Part Number: SG3843D
• Description: CURRENT MODE PWM CONTROLLER
• Manufacturer: MICROSEMI [Microsemi Corporation]

Copyright © 2000
Rev. 1.6a 10/04
The 1842/43 output stage can provide negative base current to
remove base charge of power transistor (Q
is accomplished by adding a capacitor (C
(R
The RC low pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.
1
). The resistor (R
»
FIGURE 15. — CURRENT-SENSE SPIKE SUPPRESSION
R
SG1842/43
»
1
SG1842/43
V
| | R
FIGURE 17. — BIPOLAR TRANSISTOR DRIVE
C1
V
R
C
2
2
+
_
I
B
Pin numbers referenced are for 8-pin package and pin numbers in parenthesis are for 14-pin package.
7 (12)
1
) is to limit the base current during turn on.
V
C
7 (11)
6 (10)
5 (8)
3 (5)
7 (11)
6 (10)
5 (8)
3 (5)
V
CC
C
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
R
R
2
V
IN
1
C
Q1
R
) in parallel with a resistor
S
1
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
) for faster turn off. This
U R R E N T
P
V
C
R
C1
1
1
R O D U C T I O N
I
PK(MAX)
V
= 1.0V
IN
Q1
R
- M
S
R
I
PK
S
O D E
P W M C
D
A resistor (R
ringing caused by the MOSFET input capacitance and any induc-
tance in series with the gate drive. (Note: It is very important to
have a low inductance ground path to insure correct operation of
the I.C. This can be done by making the ground paths as short and
as wide as possible.)
Current transformers can be used where isolation is required
between PWM and Primary ground. A drive transformer is then
necessary to interface the PWM output with the MOSFET.
A T A
I
SG1842/43
PK
=
V (PIN 1) - 1.4
O N T R O L L E R
FIGURE 16. — MOSFET PARASITIC OSCILLATIONS
7 (12)
S
1
) in series with the MOSFET gate reduce overshoot and
3R
H E E T
FIGURE 18. — ISOLATED MOSFET DRIVE
SG1842/SG1843 Series
7 (11)
6 (10)
5 (8)
3 (5)
S
SG1842/43
V
CC



C
7 (12)
3 (5)
Boundary
N
N
Isolation
P
S
R



7 (11)
6 (10)
5 (8)
R
S
R
1
V
IN
N
V
S
CC
Q1
R
S
V
IN
Q1
N
P
+
0
_
+
_ 0
Waveforms
50% DC
25% DC
11