Data Sheet

T
J
= T
A
+ kP
D
× R
EJA
o = 35°C +
:
0.64 W × 47°C/W
;
= 65°C
15
DRV8835
www.ti.com SLVSB18G –MARCH 2012–REVISED MAY 2016
Product Folder Links: DRV8835
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Thermal Considerations (continued)
NOTE
R
DS(on)
increases with temperature, so as the device heats, the power dissipation
increases. Consider this increase when sizing the heatsink.
The power dissipation of the DRV8835 is a function of RMS motor current and the resistance of each FET
(R
DS(ON)
), see Equation 2.
Power ≈ I
RMS
2 × (High-Side R
DS(on)
+ Low-Side R
DS(on)
) (2)
For this example, the ambient temperature is 35°C, and the junction temperature reaches 65°C. At 65°C, the
sum of R
DS(on)
is about 1 Ω. With an example motor current of 0.8 A, the dissipated power in the form of heat will
be 0.8 A
2
× 1 Ω = 0.64 W.
The temperature that the DRV8835 reaches depends on the thermal resistance to the air and PCB. It is
important to solder the device PowerPAD to the PCB ground plane, with vias to the top and bottom board layers,
in order dissipate heat into the PCB and reduce the device temperature. In the example used here, the DRV8835
had an effective thermal resistance R
θJA
of 47 ° C/W, and as shown in Equation 3.
(3)
10.3.2 Heatsinking
The PowerPAD™ package uses an exposed pad to remove heat from the device. For proper operation, this pad
must thermally connect 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 more PCB design details, refer to PowerPAD™ Thermally Enhanced Package (SLMA002) and PowerPAD™
Made Easy (SLMA004), available at www.ti.com.
In general, the more copper area that is provided, the more power can be dissipated.