Top layer copper area (cm2)

0

2

4

6

8

10

12

14

16

20

40

60

80

100

120

140

160

2L_R

2L 1oz

2L 2oz

Top layer copper area (cm2)

0

2

4

6

8

10

12

14

16

5

7.5

10

12.5

15

17.5

20

22.5

25

27.5

30

2L_P

2L 1oz

2L 2oz

Top layer copper area (cm2)

0

2

4

6

8

10

12

14

16

24

26

28

30

32

34

36

38

40

4L_R

4L 1oz

4L 2oz

Top layer copper area (cm2)

0

2

4

6

8

10

12

14

16

6.5

7

7.5

8

8.5

9

9.5

10

10.5

11

4L_P

4L 1oz

4L 2oz

24

DRV8874

SLVSF66A – AUGUST 2019 – REVISED DECEMBER 2019

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Figure 21. HTSSOP, 4-layer PCB junction-to-ambient

thermal resistance vs copper area

Figure 22. HTSSOP, 4-layer PCB junction-to-board

characterization parameter vs copper area

Figure 23. HTSSOP, 2-layer PCB junction-to-ambient

thermal resistance vs copper area

Figure 24. HTSSOP, 2-layer PCB junction-to-board

characterization parameter vs copper area

8.2.1.2.3.2

Transient Thermal Performance

The motor driver may experience different transient driving conditions that cause large currents to flow for a short

duration of time. These may include

•

Motor start-up when the rotor is not yet spinning at full speed.

•

Fault conditions when there is a supply or ground short to one of the motor outputs, and the device goes into

and out of overcurrent protection.

•

Briefly energizing a motor or solenoid for a limited time, then de-energizing.

For these transient cases, the duration of drive time is another factor that impacts thermal performance. In

transient cases, the thermal impedance parameter ZθJA denotes the junction-to-ambient thermal performance.

Figure 25 and Figure 26 show the simulated thermal impedances for 1-oz and 2-oz copper layouts for the

HTSSOP package. These graphs indicate better thermal performance with short current pulses. For short

periods of drive time, the device die size and package dominates the thermal performance. For longer drive

pulses, board layout has a more significant impact on thermal performance. Both graphs show the curves for

thermal impedance split due to number of layers and copper area as the duration of the drive pulse duration

increases. Long pulses can be considered steady-state performance.