AN2378 datasheet(5/13 Pages) STMICROELECTRONICS

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AN2378

When does L9935 open-load checking occur?

Doc ID 12435 Rev 3

5/13

When does L9935 open-load checking occur?

The flyback pulse indicates the availability of an inductive load. The flyback pulse is checked

after reversing the polarity of the motor current (full step mode), namely 61% Ishunt

(a) or

100% Ishunt, or after changing the current from 61% Ishunt to 0% Ishunt (half step mode)

(please refer to L9935 datasheet; see A.1: Reference documents).

1.1

Full step mode

Figure 2.

Output current of L9935 in full step mode

●

1full: 61% Ishunt or 100% Ishunt, regulated with chopping at low-side and slow decay

mode; flyback using the high-side path.

●

2full: reversing the polarity of the motor coil A, using fast decay (as shown in Figure 4).

During this polarity reversal, the flyback pulse is used for the open-load detection.

The process described above is also valid for motor coil B.

The symbol “Ishunt” in this application note is equivalent to the symbol “IRX” in the device datasheet.

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