PRODUCT DATABOOK 1996/1997
UC184xA/284xA/384xA
C
URRENT
M
ODE
PWM C
ONTROLLER
P
R O D U C T I O N
D
A T A
S
H E E T
T Y P I C A L A P P L I C AT I O N C I R C U I T S
FIGURE 3.
— CURRENT SENSE SPIKE SUPPRESSION
V
CC
DC BUS
FIGURE 4.
— MOSFET PARASITIC OSCILLATIONS
V
CC
DC BUS
7
Q1
7
R
1
Q1
UCx84xA
6
5
CHANGE
UCx84xA
I
PK
I
PK(MAX)
=
1.0V
R
S
6
R
S
5
3
C
R
S
The RC low pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.
A resistor (R
1
) 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
R
A
7
R
B
6
555
TIMER
8
4
UCx84xA
3
4
2
5
0.01
1.44
(R
A
+ 2R
B
)C
R
B
R
A
+ 2R
B
1
5
To other
UCx84xA devices
f=
f=
Precision duty cycle limiting as well as synchronizing several parts is
possible with the above circuitry.
6
Copyright © 1995
Rev. 1.2 12/95
MICROSEMI [ MICROSEMI CORPORATION ]
