UC3842A View Datasheet(PDF) - Motorola => Freescale
Part Name
Description
Manufacturer
UC3842A Datasheet PDF : 14 Pages
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UC3842A, 43A UC2842A, 43A
Figure 26. Current Waveform Spike Suppression
VCC
7(12)
Vin
5.0Vref
+ +–
–
+
–+
–
S
–
+
Q
R
Comp/Latch
7(11)
Q1
6(10)
5(8)
R
3(5)
C
RS
The addition of the RC filter will eliminate instability caused by the leading
edge spike on the current waveform.
Figure 27. MOSFET Parasitic Oscillations
VCC
7(12)
Vin
5.0Vref
+
+–
–
+
–+
–
S
–+
RQ
Comp/Latch
7(11)
Rg
Q1
6(10)
5(8)
3(5)
RS
Series gate resistor Rg will damp any high frequency parasitic oscillations
caused by the MOSFET input capacitance and any series wiring inductance
in the gate–source circuit.
Figure 28. Bipolar Transistor Drive
IB
Vin
+
0
Base Charge
–
Removal
C1
Q1
6(1)
5(8)
3(5)
RS
The totem–pole output can furnish negative base current for enhanced
transistor turn–off, with the addition of capacitor C1.
Figure 29. Isolated MOSFET Drive
VCC
Vin
7(12)
5.0Vref
+ +–
–
+– +
–
S
–+ RQ
Comp/Latch
Isolation
Boundary
7(11)
6(1)
VGS Waveforms
Q1
+
ÉÉÉÉ 0
–
ÉÉÉÉÉ 50% DC
+
0
–
25% DC
5(8)
R
Ipk =
V(pin 1) – 1.4
3 RS
NP
NS
3(5) C
RS NS
Np
Figure 30. Latched Shutdown
MCR
2N
101
3905
8(14)
4(7)
2(3)
1(1)
2N
3903
R
Bias
R
Osc
+
+
–
EA
1.0mA
2R
R
5(9)
The MCR101 SCR must be selected for a holding of less than 0.5 mA at
TA(min). The simple two transistor circuit can be used in place of the SCR as
shown. All resistors are 10 k.
Figure 31. Error Amplifier Compensation
From VO
Ri
Rd CI
2.5V +
2(3)
+
1.0mA
–
Rf
EA
2R
R
1(1)
5(9)
Error Amp compensation circuit for stabilizing any current–mode topology except
for boost and flyback converters operating with continuous inductor current.
From VO
Rp Ri
Cp
Rd CI
2.5V +
2(3)
Rf
+–
EA
1.0mA
2R
R
1(1)
5(9)
Error Amp compensation circuit for stabilizing current–mode boost and flyback
topologies operating with continuous inductor current.
12
MOTOROLA ANALOG IC DEVICE DATA
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