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## DRV8889-Q1 Datasheet(PDF) 61 Page - Texas Instruments

 Part No. DRV8889-Q1 Description DRV8889-Q1, DRV8889A-Q1 Automotive Stepper Driver with Integrated Current Sense, 1/256 Micro-Stepping, and Stall Detection Download 88 Pages Scroll/Zoom 100% Maker TI [Texas Instruments] Homepage http://www.ti.com Logo

## DRV8889-Q1 Datasheet(HTML) 61 Page - Texas Instruments

 61 / 88 page 8.2.4 Thermal ApplicationThis section presents the power dissipation calculation and junction temperature estimation of the device.8.2.4.1 Power DissipationThe total power dissipation constitutes of three main components - conduction loss (PCOND), switching loss(PSW) and power loss due to quiescent current consumption (PQ).8.2.4.1.1 Conduction LossThe current path for a motor connected in full-bridge is through the high-side FET of one half-bridge and low-sideFET of the other half-bridge. The conduction loss (PCOND) depends on the motor rms current (IRMS) and high-side (RDS(ONH)) and low-side (RDS(ONL)) on-state resistances as shown in Equation 4.PCOND = 2 x (IRMS)2 x (RDS(ONH) + RDS(ONL))(4)The conduction loss for the typical application shown in Section 8.2.1 is calculated in Equation 5.PCOND = 2 x (IRMS)2 x (RDS(ONH) + RDS(ONL)) = 2 x (500-mA / √2)2 x (0.45-Ω + 0.45-Ω) = 225-mW(5)NoteThis power calculation is highly dependent on the device temperature which significantly effects thehigh-side and low-side on-resistance of the FETs. For more accurate calculation, consider thedependency of on-resistance of FETs with device temperature.8.2.4.1.2 Switching LossThe power loss due to the PWM switching frequency depends on the slew rate (tSR), supply voltage, motor RMScurrent and the PWM switching frequency. The switching losses in each H-bridge during rise-time and fall-timeare calculated as shown in Equation 6 and Equation 7.PSW_RISE = 0.5 x VVM x IRMS x tRISE_PWM x fPWM(6)PSW_FALL = 0.5 x VVM x IRMS x tFALL_PWM x fPWM(7)Both tRISE_PWM and tFALL_PWM can be approximated as VVM/ tSR. After substituting the values of variousparameters, and assuming 105 V/µs slew rate and 30-kHz PWM frequency, the switching losses in each H-bridge are calculated as shown below -PSW_RISE = 0.5 x 13.5-V x (500-mA / √2) x (13.5-V / 105 V/µs) x 30-kHz = 9.2-mW(8)PSW_FALL = 0.5 x 13.5-V x (500-mA / √2) x (13.5-V / 105 V/µs) x 30-kHz = 9.2-mW(9)The total switching loss (PSW) is calculated as twice the sum of rise-time (PSW_RISE) switching loss and fall-time(PSW_FALL) switching loss as shown below -PSW = 2 x (PSW_RISE + PSW_FALL) = 2 x (9.2-mW + 9.2-mW) = 36.8-mW(10)www.ti.comDRV8889-Q1SLVSEE9C – APRIL 2020 – REVISED AUGUST 2020Copyright © 2020 Texas Instruments IncorporatedSubmit Document Feedback61Product Folder Links: DRV8889-Q1