DRV8805 Datasheet, PDF (10/16 Pages) Texas Instruments – UNIPOLAR STEPPER MOTOR DRIVER IC

DRV8805
SLVSAW3A – JULY 2011 – REVISED JULY 2011
THERMAL INFORMATION
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Thermal Protection
The DRV8805 has thermal shutdown (TSD) as described above. 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 TSD is an indication of either excessive power dissipation, insufficient
heatsinking, or too high an ambient temperature.
Power Dissipation
Power dissipation in the DRV8805 is dominated by the power dissipated in the output FET resistance, or
RDS(ON). Average power dissipation of each FET when running a static load can be roughly estimated by
Equation 1:
P = R_DS(ON) · (I_OUT)²
(1)
where P is the power dissipation of one FET, R_DS(ON) is the resistance of each FET, and I_OUT is equal to the
average current drawn by the load. Note that at start-up and fault conditions this current is much higher than
normal running current; these peak currents and their duration also need to be taken into consideration. When
driving more than one load simultaneously, the power in all active output stages must be summed.
The maximum amount of power that can be dissipated in the device is dependent on ambient temperature and
heatsinking.
Note that R_DS(ON) increases with temperature, so as the device heats, the power dissipation increases. This must
be taken into consideration when sizing the heatsink.
Heatsinking
The DRV8805 package uses a standard SOIC outline, but has the center pins internally fused to the die pad in
order to more efficiently remove heat from the device. The two center leads on each side of the package should
be connected together to as large a copper area on the PCB as is possible to remove heat from the device. If the
copper area is on the opposite side of the PCB from the device, thermal vias are used to transfer the heat
between top and bottom layers.
In general, the more copper area that can be provided, the more power can be dissipated.
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