SLVSGV9 august 2023 DRV8213
PRODUCTION DATA
Large inrush current occurs during motor start up because motor speed is low. As the motor accelerates, the motor current drops to an average level because the back electromotive force (EMF) in the motor increases with speed. The inrush current should not be mistaken for a stall condition, so the DRV8213 integrates a timing circuit in the RTE package variant to ignore the inrush current during the startup time, tINRUSH. The timing circuit is configured using a capactior, CINRUSH, on the TINRUSH pin. Section 8.4.3 describes the overall details for using the stall detection feature.
When designing for the tINRUSH time, it is important to include enough margin to account for tolerances and variation in the DRV8213 and the system overall. Equation 4 defines the minimum tINRUSH time, tINRUSH_min. The timing tINRUSH_motor should be determined experimentally because it depends on motor parameters, supply voltage, temperature, and mechanical load response times. The ϵTINRUSH term accounts for tolerances in the TINRUSH timing circuit and the CINRUSH capacitor.
Equation 5 shows the expression for finding ϵTINRUSH. The tolerance of the 1-V reference on the TINRUSH pin is ϵVTINRUSH_trip. This tolerance is 3%, as defined by the minimum and maximum specifications for VTINRUSH_trip in the Electrical Characteristics table. The tolerance of the 10-µA current source on the TINRUSH pin is ϵITINRUSH. This tolerance is 20%, as defined by the minimum and maximum specifications for ITINRUSH in the Electrical Characteristics table. The tolerance of the CINRUSH capacitor is ϵCINRUSH. This is a percentage defined by the tolerance of the selected CINRUSH capacitor.
For example, assume tINRUSH_motor = 100 ms and a capacitor with 1% tolerance will be used for CINRUSH. In this case, it can be calculated that the CINRUSH capacitor should be larger than 18.5 nF, so a 22 nF capacitor will be sufficient in this application.