MC33065 View Datasheet(PDF) - Motorola => Freescale
Part Name
Description
Manufacturer
MC33065 Datasheet PDF : 15 Pages
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MC34065 MC33065
Figure 21. Adjustable Reduction of Clamp Level
with Soft–Start
VCC
Vin
16
Vref
15
R
5.0 Vref
+
17 V
–+
Bias
_
R
+
1
20 k
+–
3
Osc
2
_
PWM
Latch 1
Q1
7
4
+
–
EA1
VClamp –
2R
+
0.5 V R
S
Q
R
R2 5
6 RS
C R1 MPSA63
Where: 0 ≤ VClamp ≤ 0.5 V
[ Ipk(max)
VClamp
RS
ǒ Ǔ [ ) VClamp
1.67
R2 1
R1
+ tSoft–Start
ln
1
1– VC
) C
R1R2
R1 R2
3 VClamp
Figure 22. MOSFET Parasitic Oscillations
VCC
Vin
16
5.0 Vref
+
+–
–
+
17 V
–+
_
Rg Q1
PWM
Latch 1
S
–
+
Q
R
7 D1
1N5819
6
RS
Series gate resistor Rg may be needed to damp high frequency
parasitic oscillations caused by the MOSFET input capacitance
and any series wiring inductance in the gate–source circuit. Rg
will decrease the MOSFET switching speed. Schottky diode
D1 is required if circuit ringing drives the output pin below
ground.
Figure 23. Current Sensing Power MOSFET
VCC
Vin
16
5.0 Vref
+
+–
_
+
17 V
–+
_
PWM
Latch 1
S
–
+
Q
R
Control Circuitry
Ground to Pin 8
D SENSEFET
S Power Ground to
G
Input Source Return
7
K
M
Drive Ground
to Pin 9
6 RS
1/4W
[ ) VPin 6
RS Ipk RDS(on)
RDM(on) RS
If: SENSEFET = MTP10N10M
RS = 200
Then: VPin 6 = 0.075 Ipk
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 19 and 21.
Figure 24. Current Waveform Spike Suppression
VCC
Vin
16
5.0 Vref
+
+–
–
+
17 V
–+
_
PWM
7
Latch 1
S
–
+
Q
R
Q1
R
6 C RS
The addition of the RC filter will eliminate instability caused by
the leading edge spike on the current waveform.
MOTOROLA ANALOG IC DEVICE DATA
11
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