DRV8825

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SLVSA73F – APRIL 2010 – REVISED JULY 2014

Feature Description (continued)

Figure 7. Decay Mode

The DRV8825 supports fast decay, slow decay and a mixed decay mode. Slow, fast, or mixed decay mode is

selected by the state of the DECAY pin; logic low selects slow decay, open selects mixed decay operation, and

logic high sets fast decay mode. The DECAY pin has both an internal pullup resistor of approximately 130 k

Ω

and an internal pulldown resistor of approximately 80 k

Ω. This sets the mixed decay mode if the pin is left open

or undriven.

Mixed decay mode begins as fast decay, but at a fixed period of time (75% of the PWM cycle) switches to slow

decay mode for the remainder of the fixed PWM period. This occurs only if the current through the winding is

decreasing (per the indexer step table); if the current is increasing, then slow decay is used.

8.3.4 Blanking Time

After the current is enabled in an H-bridge, the voltage on the xISEN pin is ignored for a fixed period of time

before enabling the current sense circuitry. This blanking time is fixed at 3.75

μs. Note that the blanking time also

sets the minimum on time of the PWM.

8.3.5 Microstepping Indexer

Built-in indexer logic in the DRV8825 allows a number of different stepping configurations. The MODE0 through

MODE2 pins are used to configure the stepping format as shown in Table 1.

Table 1. Stepping Format

MODE2

MODE1

MODE0

STEP MODE

0

0

0

Full step (2-phase excitation) with 71% current

0

0

1

1/2 step (1-2 phase excitation)

0

1

0

1/4 step (W1-2 phase excitation)

0

1

1

8 microsteps/step

1

0

0

16 microsteps/step

1

0

1

32 microsteps/step

1

1

0

32 microsteps/step

1

1

1

32 microsteps/step

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