DRV8802-Q1_15 Datasheet, PDF (17/26 Pages) Texas Instruments – DRV8802-Q1 Automotive DC Motor-Driver IC

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DRV8802-Q1
SLVSCI2A – JUNE 2014 – REVISED JUNE 2014
Thermal Information (continued)
10.3.2 Power Dissipation
Power dissipation in the DRV8802-Q1 device is dominated by the power dissipated in the output FET resistance,
or r_DS(on). Use Equation 4 to calculate the estimated average power dissipation of each H-bridge when running a
DC motor.
P_D = 2 ´ r_DS(on) ´ I_O2
where
• P_D is the power dissipation of one H-bridge
• r_DS(on) is the resistance of each FET
• I_O is the RMS output current being applied to each winding
(4)
I_O is equal to the average current drawn by the DC motor. Note that at startup and fault conditions this current is
much higher than normal running current; these peak currents and the current duration must also be considered.
The factor of 2 exists because at any instant two FETs are conducting winding current (one high-side and one
low-side).
The total device dissipation is the power dissipated in each of the two H-bridges added together.
The maximum amount of power that can be dissipated in the device is dependent on ambient temperature and
heatsinking.
NOTE
r_DS(on) increases with temperature, so as the device heats, the power dissipation
increases. This fact must be taken into consideration when sizing the heatsink.
10.3.3 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 connection can be accomplished by adding a number of vias to connect the thermal pad to the ground plane.
On PCBs without internal planes, a 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 the TI application report, PowerPAD™ Thermally Enhanced
Package (SLMA002), "" and the TI application brief, PowerPAD Made Easy™ (SLMA004), available at
www.ti.com.
In general, the more copper area that can be provided, the more power can be dissipated.
Copyright © 2014, Texas Instruments Incorporated
Product Folder Links: DRV8802-Q1
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