Datasheet

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P = HS - R I LS - R I

TOT DS(ON) OUT(RMS) DS(ON) OUT(RMS)

( ) + ( )· ·

2 2

DRV8833

SLVSAR1C –JANUARY 2011–REVISED JANUARY 2013

www.ti.com

THERMAL INFORMATION

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.

(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™ packages (PWP and RTY) use 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.

It is important to note that the PW package option is not thermally enhanced and it is recommended to adhere to

the power dissipation limits.

Product Folder Links: DRV8833