MC33981BHFK Freescale Semiconductor, MC33981BHFK Datasheet - Page 32

• Manufacturer Part Number: MC33981BHFK
• Description: HF 4.0MOHM RDSON SWITCH
• Manufacturer: Freescale Semiconductor

DC MOTOR 200W
frequency of 20 kHz, and an ambient temperature of 85 ºC
are chosen. The 33981 is evaluated using the following
board. The thermal impedance of the board is in the range of
15 ºC/W.
POWER DISSIPATION
The conditions are listed in
dissipation of 3.1 W is obtained with a duty of 95%.
32
33981
TYPICAL APPLICATIONS
POWER DISSIPATION
Figure 40. Power Dissipation (Pon and Pswitching) vs.
A concrete example is the 33981. A 200 W DC motor, a
Figure 40
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
10
Figure 39. 33981 Evaluation Board
illustrates the power dissipation in the 33981.
20
MC33981 Power Dissipation
30
Duty Cycle
Duty Cycle (%)
40
Figure
Pon_state
P switching
Ptotal
50
38. Maximum power
60
70
80
90
100
INFLUENCE OF SR CAPACITOR
losses.
losses versus the total power dissipation for the same load
conditions as
the higher the switching losses. They can be more than 50%
of the total power dissipation in the 33981 with a 4.7 nF
capacitor and is a basic applications trade-off. A compromise
should be found between the power dissipation and the
electromagnetic capability (EMC) performance.
RECIRCULATION PHASE
recirculation approaches, diode or low side MOSFET. The
power dissipation gain for the entire system when using the
low side instead of the diode can reach up to 1.5 W with a
duty cycle of 50%.
The SR capacitor value has an impact on these switching
Figure 42
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
6
6
5
5
4
4
3
3
2
2
1
1
0
0
0
Figure 41. Power Switching vs. SR Capacitor
Figure 41
Figure 42. Total Board Power Dissipation
10
Total Board Power Dissipation
20
0
0
illustrates the power dissipation for the two
Figure
30
Ratio PWM %
illustrates the percentage of the switching
40
38. The higher the SR capacitor value,
50
Analog Integrated Circuit Device Data
60
P switch in g
P switch in g
P o n
P o n
2 .2
2 .2
70
C s r (n F )
C s r (n F )
80
90
Freescale Semiconductor
100
3 .3
3 .3
Power HS
Power Diode
Power Total Board with Diode
Power LS
Power Total Board with LS
4 .7
4 .7