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7.3.9.1 Slow Decay

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OFF

DRIVE

TRIP

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OFF

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TRIP

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OFF

Figure 7-12. Slow Decay Mode

During slow decay, both the low-side FETs of the H-bridge are turned on, allowing the current to be recirculated.

Here are the points to consider when selecting slow decay mode -

• Slow decay exhibits the least current ripple of the decay modes for a given tOFF.

• However on decreasing current steps, slow decay will take a long time to settle to the new ITRIP level because

the current decreases very slowly.

– If the current at the end of the off time is above the ITRIP level, slow decay will be extended for another off

time duration and so on, till the current at the end of the off time is below ITRIP level.

• In cases where current is held at the same level for a long time (no STEP input), or the target regulation

current level is low, or at very low stepping speeds, slow decay may not properly regulate current because

the back-EMF across the motor windings may be very small to discharge the current during the off time. In

this state, motor current can rise very quickly, and may require a large off time. In some cases this may cause

a loss of current regulation, and a more aggressive decay mode is recommended.

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DRV8461

SLOSE98 – DECEMBER 2022

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DRV8461SPWPR 数据表(PDF) 31 Page - Texas Instruments