DRV8461SPWPR datasheet(36/117 Pages) TI

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DRV8461

RSENSE

OP-AMP

Controller

(Motor Health

or FOC

)

Figure 7-16. Current Sensing with External Resistor

No current flows through the sense resistor during the slow decay, so the sense resistor conducts less than

the coil RMS current. Place the sense resistors as close as possible to the corresponding IC pins. Use a

symmetrical sense resistor layout to ensure good matching. Low-inductance sense resistors should be used

to prevent voltage spikes and ringing. For optimal performance, the sense resistor should be a surface-mount

resistor rated for high enough power.

7.3.11 Silent step decay mode

Conventional peak current mode control looks at instantaneous current in the sensing MOSFETs to determine

drive and decay durations. As a result, the motor driver reacts to instantaneous inaccuracies in the system.

These sudden changes in current cause audible noise from the motor.

To ensure noiseless stepper motor operation, the DRV8461 features the silent step decay mode. The silent step

is a voltage mode PWM regulation scheme to remove noise due to PWM switching at standstill and low speeds.

Thus, silent step operated stepper motor applications are highly suitable for applications such as 3D printer,

medical equipment and factory automation, where low noise operation is critical.

Note

When the device is operating with silent step decay mode -

• Open-load fault detection works only when the motor is in motion, but not if the motor is in

standstill.

• Stall detection is not supported.

• Spread spectrum feature is disabled.

The silent step loop is designed for low bandwidth operation, therefore at moderate to high motor speeds, the

decay mode can be switched back to one of the conventional current-mode decay schemes programmed by the

DECAY bits. Transition from silent step to another decay mode is immediate, whereas the transition from other

decay modes to silent step happens at the boundary of electrical half-cycles.

Figure 7-17 shows the block diagram of the silent step decay mode implementation -

DRV8461

SLOSE98 – DECEMBER 2022

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DRV8461SPWPR датащи(PDF) 36 Page - Texas Instruments