UC3845AD Microsemi Analog Mixed Signal Group, UC3845AD Datasheet - Page 6

• Manufacturer Part Number: UC3845AD
• Description: IC CTRLR PWM CURRENT MODE 14SOIC
• Manufacturer: Microsemi Analog Mixed Signal Group

Specifications of UC3845AD

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 500kHz
• Duty Cycle: 50%
• Voltage - Supply: 8.2 V ~ 25 V
• Buck: Yes
• Boost: Yes
• Flyback: Yes
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• Frequency-max: 500kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

UC184xA/284xA/384xA
6
The RC low pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.
UCx84xA
FIGURE 3. — CURRENT SENSE SPIKE SUPPRESSION
7
6
5
3
V
CC
FIGURE 5. — EXTERNAL DUTY CYCLE CLAMP AND MULTI-UNIT SYNCHRONIZATION
CHANGE
f =
f =
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
R
(R
A
B
A
DC BUS
A
+ 2R
R
1.44
+ 2R
B
C
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
Q1
R
B
U R R E N T
P
S
B
)C
7
6
2
0.01
R O D U C T I O N
Precision duty cycle limiting as well as synchronizing several parts is
possible with the above circuitry.
I
PK(MAX)
8
5
TIMER
=
555
M
1.0V
R
4
I
O D E
S
PK
1
P W M C
UCx84xA devices
3
D
A resistor (R
& 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.)
To other
A T A
O N T R O L L E R
8
4
FIGURE 4. — MOSFET PARASITIC OSCILLATIONS
1
S
) in series with the MOSFET gate will reduce overshoot
H E E T
UCx84xA
UCx84xA
5
5
7
6
V
CC
R
1
DC BUS
Q1
R
S
Copyright © 1995
Rev. 1.2a 10/25