DRV8833 Datasheet, PDF (12/22 Pages) Texas Instruments – DUAL H-BRIDGE MOTOR DRIVER

DRV8833
SLVSAR1B – JANUARY 2011 – REVISED AUGUST 2011
THERMAL INFORMATION
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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 datasheet 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 via measurement or
thermal simulation.
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.
Power Dissipation
Power dissipation in the DRV8833 is dominated by the DC power dissipated in the output FET resistance, or
RDS(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 2.
P_TOT
=
(HS
-
R_DS(ON)
·
I )2
OUT(RMS)
+
(LS
-
R_DS(ON)
·
I )2
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, and I_OUT(RMS) is the RMS output current being applied to the motor.
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 PowerPAD™ package uses an exposed pad to remove heat from the device. For proper operation, this pad
must be thermally connected to copper on the PCB to dissipate heat. On a multi-layer PCB with a ground plane,
this can be accomplished by adding a number of vias to connect the thermal pad to the ground plane. On PCBs
without internal planes, copper area can be added on either side of the PCB to dissipate heat. 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.
For details about how to design the PCB, refer to TI application report SLMA002, " PowerPAD™ Thermally
Enhanced Package" and TI application brief SLMA004, " PowerPAD™ Made Easy", available at www.ti.com.
In general, the more copper area that can be provided, the more power can be dissipated.
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