P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
SG1842/SG1843 Series
C
U R R E N T - M O D E P W M C O N T R O L L E R
P R O D U C T I O N D A T A S H E E T
TYPICAL APPLICATION CIRCUITS
Pin numbers referenced are for 8-pin package and pin numbers in parenthesis are for 14-pin package.
VCC
V
V
VCC
IN
IN
7 (12)
7 (12)
7 (11)
7 (11)
Q1
Q1
R
1
6 (10)
5 (8)
SG1842/ 43
SG1842/ 43 6 (10)
I
PK
R
1.0V
3 (5)
I
=
5 (8)
PK(MAX)
R
S
R
C
S
R
S
3 (5)
FIGURE 16. — MOSFET PARASITIC OSCILLATIONS
FIGURE 15. — CURRENT-SENSE SPIKE SUPPRESSION
The RC low pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.
A resistor (R1) in series with the MOSFET gate reduce overshoot and
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.)
VCC
V
IN
IB
VC
+
_
»
V
R
IN
2
Isolation
7 (12)
Boundary
VC1
R || R
»
7 (11)
Q1
1
2
VC1
C1
6 (10)
Waveforms
VC
+
7 (11)
6 (10)
SG1842/ 43
0
_
R
2
5 (8)
3 (5)
50% DC
25% DC
Q1
SG1842/ 43
+
R
1
R
0
_
R
NS
NP
S
C
5 (8)
3 (5)
NP
NS
V (PIN 1) - 1.4
3RS
R
S
IPK
=
FIGURE 17. — BIPOLAR TRANSISTOR DRIVE
FIGURE 18. — ISOLATED MOSFET DRIVE
The 1842/43 output stage can provide negative base current to
remove base charge of power transistor (Q1) for faster turn off. This
is accomplished by adding a capacitor (C1) in parallel with a resistor
(R1). The resistor (R1) is to limit the base current during turn on.
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.
Copyright © 2000
Rev. 1.6 4/00
11
MICROSEMI [ Microsemi ]
