UC3845AD Microsemi Analog Mixed Signal Group, UC3845AD Datasheet - Page 7

• 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

Copyright © 1995
Rev. 1.2a 10/25
From V
R
R
i
d
2N222A
Due to inherent instability of current mode converters running above 50% duty cycle, slope compensation should be added to either
the current sense pin or the error amplifier. Figure 6 shows a typical slope compensation technique.
High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be
connected to pin 5 in a single point ground. The transistor and 5k potentiometer are used to sample the oscillator waveform and apply an
adjustable ramp to pin 3.
O
R
C
SLOPE
F
C
T
ERROR AMP
ADJUST
8(14)
R
R
4(7)
2(3)
1(1)
T
F
4.7K
4.7K
1K
ERROR
OSCILLATOR
AMP
5V
ADJUST
100K
2N2222
2.5V
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
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
I
SENSE
5K
UVLO
C
U R R E N T
P
R O D U C T I O N
2R
FIGURE 7. — OPEN LOOP LABORATORY FIXTURE
R
T
5(9)
R
FIGURE 6. — SLOPE COMPENSATION
GOOD LOGIC
1
2
3
4
S
UCx84xA
R
COMP
V
I
R
M
1V
SENSE
V
T
FB
REF
C
T
O D E
REF
5V
UCx84xA
COMP
C.S.
C
GROUND
P W M C
T
OUTPUT
D
V
LATCH
V
PWM
REF
CC
A T A
8
7
6
5
INTERNAL
O N T R O L L E R
UC184xA/284xA/384xA
BIAS
S
0.1µF
H E E T
0.1µF
(continued)
7(12)
A
1K
7(11)
6(10)
5(8)
3(5)
V
CC
C
R
DC BUS
V
V
OUTPUT
GROUND
R
Q1
REF
CC
S
V
O
7