P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
UC184xA/284xA/384xA
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
FIGURE 4. — MOSFET PARASITIC OSCILLATIONS
FIGURE 3. — CURRENT SENSE SPIKE SUPPRESSION
VCC DC BUS
VCC
DC BUS
7
6
7
Q1
RS
R1
Q1
UCx84xA
UCx84xA
6
5
IPK
CHANGE
3
1.0V
RS
IPK(MAX)
=
C
5
RS
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 will reduce overshoot
& ringing caused by the MOSFET input capacitance and any
inductance 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.)
FIGURE 5. — EXTERNAL DUTY CYCLE CLAMP AND MULTI-UNIT SYNCHRONIZATION
8
4
8
4
RA
RB
7
6
UCx84xA
555
TIMER
3
2
5
1
5
0.01
To other
UCx84xA devices
1.44
f =
f =
(RA + 2RB)C
RB
Precision duty cycle limiting as well as synchronizing several parts is
possible with the above circuitry.
RA + 2RB
Copyright © 1995
Rev. 1.2 12/95
6
MICROSEMI [ Microsemi ]
