DRV8317 datasheet(63/69 Pages) TI

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11.3 Thermal Considerations

The DRV8317 has thermal shutdown (OTS) as previously described. A die temperature in excess of 145°C

(min.) can disable the device until the temperature drops to a safe level.

Any tendency of the device to enter thermal shutdown is an indication of excessive power dissipation, insufficient

heatsinking, or too high an ambient temperature.

11.3.1 Power Dissipation and Junction Temperature Estimation

Power Dissipation

The power loss in DRV8317 include standby losses, LDO losses, FET conduction and switching losses, and

diode losses. The FET conduction loss dominates the total power dissipation in DRV8317. At start-up and fault

conditions, the output current is much higher than normal current; remember to take these peak currents and

their duration into consideration. The total device dissipation is the power dissipated in each of the three half

bridges added together. The maximum amount of power that the device can dissipate depends on ambient

temperature and heatsinking. Note that RDS,ON increases with temperature, so as the device heats, the power

dissipation increases. Take this into consideration when designing the PCB and heatsinking.

A summary of equations for calculating each loss is listed in Table 11-1 for trapezoidal control and field-oriented

control.

Table 11-1. DRV8317 Power Losses for Trapezoidal and Field-oriented Control

Loss type

Trapezoidal control

Field-oriented control

Standby power

Pstandby = VVM x IVMS

AVDD LDO

PLDO = (VVIN_AVDD - VAVDD) x IAVDD

FET conduction

PCON = 2 x (IPK(trap))2 x RDS,ON(TJ)

PCON = 3 x (IRMS(FOC))2 x RDS,ON(TJ)

FET switching

PSW = IPK(trap) x VPK(trap) x trise/fall x fPWM

PSW = 3 x IRMS(FOC) x VPK(FOC) x trise/fall x

fPWM

Diode (dead time)

Pdiode = 2 x IPK(trap) x VF(diode) x tDEAD x fPWM

Pdiode = 6 x IRMS(FOC) x VF(diode) x tDEAD x

fPWM

Note

RDS,ON (TJ) is the on-state resistance of a single FET at operating junction temperature.

Junction Temperature Estimation

To calculate the junction temperature of the die from power losses, use Equation 5. Note that the thermal

resistance RθJA depends on PCB configuration such as the numbers of PCB layers, copper thickness, ground

plane area and the PCB size.

TJ℃ =PLOSSW ×RθJA℃/W +TA℃

(5)

Refer to BLDC integrated MOSFET thermal calculator for estimating the approximate device power dissipation

and junction temperature at different use cases.

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DRV8317

SLVSGT3 – DECEMBER 2022

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