ZHCSOY8B September 2021 – February 2022 DRV8311
PRODUCTION DATA
Power Dissipation
The power loss in DRV8311 include standby power losses, LDO power losses, FET conduction and switching losses, and diode losses. The FET conduction loss dominates the total power dissipation in DRV8311. 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 12-1 for trapezoidal control and field-oriented control.
| Loss type | Trapezoidal control | Field-oriented control |
|---|---|---|
| Standby power | Pstandby = VVM x IVM_TA | |
| LDO (from VM) | PLDO = (VVIN_AVDD - VAVDD) x IAVDD | |
| FET conduction | PCON = 2 x (IPK(trap))2 x RDS,ON(TA) | PCON = 3 x (IRMS(FOC))2 x RDS,ON(TA) |
| 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 |
Junction Temperature Estimation
To calculate the junction temperature of the die from power losses, use Equation 17. Note that the thermal resistance RθJA depends on PCB configurations such as the ambient temperature, numbers of PCB layers, copper thickness, and the PCB size.
Refer BLDC integrated MOSFET thermal calculator for estimating the approximate device power dissipation and junction temperature at different use cases.