DRV8833_16 Datasheet, PDF (16/30 Pages) Texas Instruments – Dual H-Bridge Motor Driver

DRV8833
SLVSAR1E – JANUARY 2011 – REVISED JULY 2015
www.ti.com
10.3 Thermal Considerations
10.3.1 Maximum Output Current
In actual operation, the maximum output current achievable with a motor driver is a function of die temperature.
This, in turn, is greatly affected by ambient temperature and PCB design. Basically, the maximum motor current
will be the amount of current that results in a power dissipation level that, along with the thermal resistance of the
package and PCB, keeps the die at a low enough temperature to stay out of thermal shutdown.
The dissipation ratings given in the data sheet can be used as a guide to calculate the approximate maximum
power dissipation that can be expected to be possible without entering thermal shutdown for several different
PCB constructions. However, for accurate data, the actual PCB design must be analyzed through measurement
or thermal simulation.
10.3.2 Thermal Protection
The DRV8833 has thermal shutdown (TSD) as described above. If the die temperature exceeds approximately
150°C, the device will be disabled until the temperature drops by 45°C.
Any tendency of the device to enter TSD is an indication of either excessive power dissipation, insufficient
heatsinking, or too high an ambient temperature.
10.4 Power Dissipation
Power dissipation in the DRV8833 is dominated by the DC power dissipated in the output FET resistance, or
R_DS(ON). There is additional power dissipated due to PWM switching losses, which are dependent on PWM
frequency, rise and fall times, and VM supply voltages. These switching losses are typically on the order of 10%
to 30% of the DC power dissipation.
The DC power dissipation of one H-bridge can be roughly estimated by Equation 3.
    ³TOT ^{  +6 ± 5}DS(ON) ^{u ,}OUT(RMS)2 ^{ /6 ± 5}DS(ON) ^{u ,}OUT(RMS)2
where
• P_TOT is the total power dissipation
• HS - R_DS(ON) is the resistance of the high-side FET
• LS - R_DS(ON) is the resistance of the low-side FET
• I_OUT(RMS) is the RMS output current being applied to the motor
(3)
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.
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