DRV8823-Q1_15 Datasheet, PDF (13/22 Pages) Texas Instruments – 4-BRIDGE SERIAL INTERFACE MOTOR DRIVER

DRV8823-Q1
www.ti.com
THERMAL INFORMATION
SLVSBH2B – JUNE 2012 – REVISED JANUARY 2013
Thermal Protection
The DRV8823-Q1 device has thermal shutdown (TSD) as described above. If the die temperature exceeds
approximately 150°C, the device is 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.
Power Dissipation
Power dissipation in the DRV8823-Q1 device 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 Equation 2.
P_TOT = 4 x R_DS(ON) x (I_OUT(RMS) )²
(2)
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 applied to each winding. I_OUT(RMS) is equal to approximately 0.7x the full-scale output current setting. The
factor of 4 is derived from the two motor windings, and at any instant two FETs are conducting winding current
for each winding (one high-side and one low-side). The DRV8823-Q1 device has two stepper motor drivers, so
the power dissipation of each must be added together to determine the total device power dissipation.
The maximum amount of power that can be dissipated in the DRV8823-Q1 device is dependent on ambient
temperature and heatsinking. The thermal dissipation ratings table in the datasheet can be used to estimate the
temperature rise for typical PCB constructions.
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 integrated circuit 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. Figure 5 shows
thermal resistance versus copper plane area for both a single-sided PCB with 2-oz copper heatsink area, and a
4-layer PCB with 1-oz copper and a solid ground plane. Both PCBs are 76 mm x 114 mm, and 1.6 mm thick. The
heatsink effectiveness increases rapidly to about 20 cm², then levels off somewhat for larger areas.
Six pins on the center of each side of the package are also connected to the device ground. A copper area can
be used on the PCB that connects to the PowerPAD integrated circuit package as well as to all the ground pins
on each side of the device, which is especially useful for single-layer PCB designs.
Copyright © 2012–2013, Texas Instruments Incorporated
Product Folder Links: DRV8823-Q1
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