DRV8818_15 Datasheet, PDF (21/31 Pages) Texas Instruments – DRV8818 Stepper Motor Controller IC

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11.2 Layout Example
GND
GND
100 PŸ
VCC
100 PŸ
ISENA
HOMEn
DIR
AOUT1
DECAY
RCA
GND
VREF
RCB
VCC
BOUT1
USM1
USM0
ISENB
GND
GND
DRV8818
SLVSAX9D – SEPTEMBER 2011 – REVISED JANUARY 2015
VMA
SLEEPn
ENABLE
AOUT2
CP2
CP1
VCP
GND
VGD
STEP
BOUT2
RESETn
SRn
VMB
0.1 µF
VM
0.22 µF
0.22 µF
0.22 µF
GND
VM
0.1 µF
Figure 14. Layout Example Schematic
11.3 Thermal Considerations
The DRV8818 has thermal shutdown (TSD) as described previously. If the die temperature exceeds
approximately 150°C, the device will be disabled until the temperature drops to a safe level.
Any tendency of the device to enter thermal shutdown is an indication of either excessive power dissipation,
insufficient heatsinking, or too high an ambient temperature.
11.4 Power Dissipation
Power dissipation in the DRV8818 is dominated by the power dissipated in the output FET resistance, or R_DS(ON).
Average power dissipation when running a stepper motor can be roughly estimated by:
P = 4 · R · (I )²
TOT
DS(ON)
OUT(RMS)
(8)
where P_TOT is the total power dissipation, R_DS(ON) is the resistance of each FET, and I_OUT(RMS) is the RMS output
current being applied to each winding. I_OUT(RMS) is equal to the approximately 0.7x the full-scale output current
setting. The factor of 4 comes from the fact that there are two motor windings, and at any instant two FETs are
conducting winding current for each winding (one high-side and one low-side).
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