MC33023 Motorola, MC33023 Datasheet - Page 13

• Manufacturer Part Number: MC33023
• Description: High Speed Single-Ended PWM Controller
• Manufacturer: Motorola

addition of a PNP transistor to buffer the clamp voltage, the Soft–Start current
is not affected by R 1 .
at the ramp input to end a cycle.
oscillation caused by the MOSFET’s input capacitance and any series wiring
inductance in the gate–source circuit. The series resistor will also decrease the
MOSFET switching speed. A Schottky diode can reduce the driver’s power
dissipation due to excessive ringing, by preventing the output pin from being
driven below ground. The Schottky diode also prevents substrate injection when
the output pin is driven below ground.
In voltage mode operation, the maximum duty cycle can be clamped. By the
In current mode operation, this circuit will limit the maximum voltage allowed
A series gate resistor may be needed to dampen high frequency parasitic
MOTOROLA ANALOG IC DEVICE DATA
The new equation for Soft–Start is
Figure 30. Buffered Maximum Clamp Level
Figure 32. MOSFET Parasitic Oscillations
R 1
R 2
V ref
C SS
15
14
12
1
2
8
V C
t
[
V clamp
Sense Input
9.0
To Current
)
+
A
0.6
MC34023 MC33023
V in
(
C
R S
SS
)
transistor turn–off, with the addition of the capacitor in series with the base.
is recommended when driving inductive loads at high frequencies. The diode
can reduce the driver’s power dissipation due to excessive ringing, by preventing
the output pin from being driven below ground.
+
0
–
The totem pole output can furnish negative base current for enhanced
The totem pole output can easily drive pulse transformers. A Schottky diode
I B
Figure 31. Bipolar Transistor Drive
Figure 33. Isolated MOSFET Drive
Base Charge
Removal
15
14
12
V C
15
14
12
V C
Sense Input
To Current
V in
13
R S