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UC2842A View Datasheet(PDF) - Motorola => Freescale

Part NameDescriptionManufacturer
UC2842A HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER Motorola
Motorola => Freescale Motorola
UC2842A Datasheet PDF : 14 Pages
First Prev 11 12 13 14
UC3842A, 43A UC2842A, 43A
Figure 20. External Clock Synchronization
Vref
8(14)
RT
R
Bias
R
External
Sync
0.01
CT
4(7)
Input
47
2(3)
1(1)
Osc
+
+
EA
2R
R
5(9)
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.
Figure 21. External Duty Cycle Clamp and
Multi Unit Synchronization
RA
8
4
RB
6
5.0k
+
R
5
Q
3
2
+
S
7
C
5.0k MC1455
1
f=
1.44
(RA + 2RB)C
Dmax =
RB
RA + 2RB
8(14)
R
Bias
R
Osc
4(7)
+
+
2(3)
EA
2R
R
1(1)
To Additional
5(9)
UCX84XA’s
Figure 22. Adjustable Reduction of Clamp Level
VCC
7(12)
Vin
8(14)
4(7)
R2
2(3)
1(1)
R1
R
Bias
R
Osc
+
+
EA
1.0mA
2R
R
5.0Vref
+ +–
+
–+
VClamp
–+
1.0V
S
RQ
Comp/Latch
5(9)
7(11)
Q1
6(10)
5(8)
3(5)
RS
VClamp =
1.67
R2 + 1
R1
+ 0.33 x 10 – 3
R1 R2
R1 + R2
Ipk(max) =
VClamp
RS
Where: 0 VClamp 1.0 V
Figure 23. Soft–Start Circuit
8(14)
R
Bias
R
5.0Vref
+ +–
Osc
4(7)
+
2(3)
1.0M
C
1(1)
+
EA
1.0mA
2R
R
S
–+
RQ
1.0V
 tSoft–Start 3600C in µF
5(9)
Figure 24. Adjustable Buffered Reduction of
Clamp Level with Soft–Start
VCC
7(12)
Vin
8(14)
R
5.0Vref
+– +
Bias
R
+ +–
7(11)
Q1
Osc
4(7)
2(3)
R2
1(1)
+
+
1.0mA
EA
2R
R
VClamp
–+
1.0V
S
RQ
Comp/Latch
6(10)
5(8)
3(5)
RS
C
MPSA63
R1
1.67
VClamp =
R2 + 1
R1
5(9)
Ipk(max) =
VClamp
RS
tSoftstart = – In
Where: 0 VClamp 1.0 V
1–
VC
3VClamp
C
R1 R2
R1 + R2
Figure 25. Current Sensing Power MOSFET
5.0Vref
+ +–
VCC
(12)
+– +
(11)
Vin
VPin 5
=
RS Ipk rDS(on)
rDM(on) + RS
If: SENSEFET = MTP10N10M
RS = 200
Then: Vpin 5 = 0.075 Ipk
D SENSEFET
S
S
–+ R Q
Comp/Latch
Control CIrcuitry
Ground:
To Pin (9)
(10) G M
(8)
(5) RS
1/4 W
K
Power Ground
To Input Source
Return
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 Ipk(max) clamp level must be implemented. Refer to Figures 22 and 24.
MOTOROLA ANALOG IC DEVICE DATA
11
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