UC3842AN ON Semiconductor, UC3842AN Datasheet - Page 12

• Manufacturer Part Number: UC3842AN
• Description: IC CTRLR CURRENT MODE HP 8DIP
• Manufacturer: ON Semiconductor
• Type: High Performance Current Mode Controllersr

Specifications of UC3842AN

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 500kHz
• Duty Cycle: 96%
• Voltage - Supply: 11.5 V ~ 25 V
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 8-DIP (0.300", 7.62mm)
• Frequency-max: 500kHz
• Output Voltage Range: 4.9 V to 5.1 V
• Input Voltage Range: 30 V
• Operating Temperature Range: 0 C to + 70 C
• Mounting Style: Through Hole
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: UC3842ANOS

V
Clamp
C
R2
R1
External
Sync
Input
8(14)
R2
R1
4(7)
2(3)
1(1)
=
Figure 23. Adjustable Reduction of Clamp Level
Figure 21. External Clock Synchronization
8(14)
Figure 25. Adjustable Buffered Reduction of
V
4(7)
2(3)
1(1)
MPSA63
Clamp
R
R
The diode clamp is required if the Sync amplitude is large enough to
cause the bottom side of CT to go more than 300 mV below ground.
1.67
2
1
0.01
+
−
=
+ 1
EA
R
R
+
−
R
R
Clamp Level with Soft−Start
+
EA
+ 0.33 x 10 − 3
1.67
2
1
R
R
Osc
1.0mA
Bias
+
C
+ 1
R
47
T
Osc
1.0mA
T
Bias
2R
R
V
2R
ref
8(14)
I
4(7)
2(3)
1(1)
R
pk(max)
5(9)
V
t
Clamp
Softstart
R
5(9)
−
R
+
1.0V
V
1
=
5.0V
1
Clamp
+ R
−
R
+
1.0V
−
+
5.0V
UC3842A, UC3843A, UC2842A, UC2843A
+
−
2
+
−
ref
2
= − In
VClamp
−
+
EA
+
−
RS
Comp/Latch
R
R
ref
S
R
Comp/Latch
+
Q
Osc
S
R
Bias
Q
I
pk(max)
1 −
Where: 0 ≤ V
+
−
2R
Where: 0 ≤ V
+
−
R
+
3V
7(12)
−
=
+
V
Clamp
7(12)
−
C
5(9)
VClamp
Clamp
http://onsemi.com
RS
Clamp
V
CC
7(11)
6(10)
5(8)
3(5)
V
C
CC
≤ 1.0 V
7(11)
6(10)
5(8)
3(5)
≤ 1.0 V
R
R
1
1
+ R
R
12
2
Q1
Q1
R
2
V
R
V
S
in
f =
S
in
R
R
C
Virtually lossless current sensing can be achieved with the implementation of a
SENSEFET power switch. For proper operation during over current conditions, a
reduction of the I
B
(R
A
6
5
2
A
−
+
1.44
+ 2R
Figure 26. Current Sensing Power MOSFET
Figure 22. External Duty Cycle Clamp and
5.0V
−
+
+
−
B
ref
8
5.0k
1
)C
5.0k
+
−
+
−
Comp/Latch
C
S
R
pk(max)
MC1455
Q
Multi Unit Synchronization
1.0M
R
S
D
Control CIrcuitry
8(14)
Q
max
4(7)
2(3)
1(1)
+
To Pin (9)
4
−
t
Ground:
clamp level must be implemented. Refer to Figures 23 and 25.
Soft−Start
Figure 24. Soft−Start Circuit
=
+
(12)
−
R
A
 3600C in mF
R
+ 2R
+
−
B
EA
7
R
R
3
V
B
CC
(11)
(10)
(8)
(5)
+
Osc
1.0mA
Bias
G
1/4 W
R
8(14)
M
S
2R
D
4(7)
2(3)
1(1)
R
SENSEFET
V
To
Additional
UCX84XA’s
in
K
To Input Source
Power Ground
S
5(9)
If: SENSEFET = MTP10N10M
Return
V
Pin
+
−
−
+
1.0V
5.0V
Then: V
EA
5 =
R
R
−
+
+
−
+
ref
Osc
R
r
pin
Bias
S
DM(on)
R
S
R
I
S
5 = 0.075 I
pk
Q
= 200
2R
r
+ R
DS(on)
R
S
5(9)
pk