MC3479FN Datasheet, PDF (8/10 Pages) ON Semiconductor – Stepper Motor Driver

MC3479
70
60
I_OD = 0
50
40
30
20
10
0
50 100 150 200 250 300 350
I_BS (mA)
Figure 8. Power Supply Current
0.8
0.6
0.4
0.2
0
0
100
200
300
I_OD (mA)
Figure 9. Maximum Saturation Voltage −
Driver Output Low
For example, assume an application where V_M = 12 V, the
motor requires 200 mA/coil, operating at room temperature
with no heatsink on the IC. From Figure 11, I_BS is
determined to be 95 mA.
R_B is calculated:
R_B = (12 − 0.7) V/95 mA
R_B = 118.9 kW
From Figure 8, I_M (max) is determined to be 22 mA. From
Figure 9, V_OLD is 0.46 V, and from Figure 10, (V_M − V_OHD)
is 1.4 volts.
P = (12  0.022) + (2  0.2) (1.4 + 0.46)
P = 1.01 W
T_J = (1.01 W  52°C/W) + 25°C
T_J = 77.5°C
This temperature is well below the maximum limit. If the
calculated T_J had been higher than 150°C, a heatsink such
as the Staver Co. V−7 Series, Aavid #5802, or Thermalloy
#6012 could be used to reduce R_qJA. In extreme cases,
forced air cooling should be considered.
The above calculation, and R_qJA, assumes that a ground
plane is provided under the MC3479 (either or both sides of
the PC board) to aid in the heat dissipation. Single nominal
width traces leading from the four ground pins should be
avoided as this will increase T_J, as well as provide
potentially disruptive ground noise and I_R drops when
switching the motor current.
2.0
1.5
1.0
0.5
0
0
100
200
300
I_OD (mA)
Figure 10. Maximum Saturation Voltage −
Driver Output High
140.00
120.00
100.00
80.00
60.00
40.00
20.00
0.00
0.00 50.00 100.00 150.00 200.00 250.00 300.00
I_OD (mA)
Figure 11. Bias/Set Current − Output Drive Current
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