DRV8317 datasheet(57/69 Pages) TI

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Table 9-2. Summary of Delay Times in DRV8317 Depending on Logic Inputs and Output Current Direction

(continued)

OUTx Current

Direction

INHx

INLx

Propagation Delay

(tPD)

Dead Time (tDEAD) Inserted MCU Dead Time (tDEAD(MCU))

tDEAD(MCU) ≤ tDEAD

tDEAD(MCU) > tDEAD

Into OUTx

Rising

Falling

≤ tPD (typ.)

≤ tDEAD (typ.)

Output dead time ≤ tDEAD

(typ.)

Output dead time < tDEAD(MCU)

Falling

Rising

≤ tPD (max)

≤ tDEAD (max)

Output dead time ≤ tDEAD

(max)

Output dead time = tDEAD(MCU)

9.2.1.3 Delay Compensation

Differences in delays of dead time and propagation delay can cause mismatch in the output timings of PWMs,

which can lead to duty cycle distortion. In order to accommodate differences in propagation delay between the

conditions mentioned in Table 9-2, DRV8317 integrates a delay compensation feature.

Delay compensation is used to match delay times for currents going into and out of phase (OUTx) by adding a

variable delay time (tvar) to match a preset target delay time equal to the propagation delay plus driver dead time

(tPD + tDRV_DEAD). This (tvar) setting is automatically configured by the DRV8317 when the DLYCMP_EN bit is set

to 1b.

9.2.1.4 Current Sensing and Output Filtering

The SOx pins are typically sampled by an analog-to-digital converter in the MCU to calculate the phase current.

Phase current information is used for closed-loop control such as Field-Oriented Control (FOC).

An example calculation for phase current is shown in Equation 3.

SOx = VREF/2 + GCSA * IOUTx

(3)

For example, in a system with VREF = 3-V, CSA gain = 0.5 V/A, and a SOx voltage of 1.2-V, phase current

(IOUTx) = -0.6A.

Sometimes high frequency noise can appear at the SOx signals based on voltage ripple at VREF, added

inductance at the SOx traces, or routing of SOx traces near high frequency components. It is recommended to

add a low-pass RC filter close to the MCU with cut-off frequency at least 10 times the PWM switching frequency

for trapezoidal commutation and 100 times the PWM switching frequency for sinusoidal commutation to filter

high frequency noise. A recommended RC filter is 330-ohms, 22-pF to add minimal parallel capacitance to the

ADC and current mirroring circuitry without increasing the settling time of the CSA output.

The cutoff frequency for the low-pass RC filter is in Equation 4.

fc= 12πRC

(4)

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DRV8317

SLVSGT3 – DECEMBER 2022

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