UM0432 datasheet(41/53 Pages) STMICROELECTRONICS

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UM0432

Motor control operations

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7.5.10

Detecting the BEMF using the internal reference

First of all, it is necessary to correctly size the value of the R39, R50 and R63 resistors using

the following formula.

Equation 4

Set the jumper as described in Table 14.

You must then configure the firmware. To do this, remove the comment in the following

define in the spec_settings.h file.

#define BEMF_SAMPLING_DURING_TON

To set the motor to run at 100% of the duty cycle, change the following defines in the

spec_settings.h file:

#define RV1_SEL 0

#define steady_duty

((u8)255)

#define Max_Duty ((u16)(((u16)(mem_MCPOH)<<16)+mem_MCPOL)+1)

This is the default configuration and the BEMF sampling is performed using the 2.5-V

internal reference.

7.5.11

Detecting the BEMF using the external reference VBus/2

The system can be set up to use VBus/2 as the external reference. In this case, in addition to

the settings described in Section 7.5.10, you must replace R74 using the formula:

Equation 5

Also set J21 between pins 2 and 3 and change the following define in the mtc.h file.

#define mem_MCRC_GE ((u8)71)

You must then calculate VBusth using the formula:

Equation 6

and modify the following define in the adc.c file replacing the calculated value:

#define HVBUS_THRESHOLD

VBusth

7.5.12

Detecting the BEMF using the external reference and reconstructed

neutral point of the motor

The system can also be configured to use the reconstructed neutral point of the motor as

reference.

To do this – in addition to the settings described in Section 7.5.10 – you must mount the R71

resistor with the same value as R39, R50 and R63, and set J21 between pins 1 and 2.

39 50 63

55000

Vbus

--------------

⎝⎠

⎛⎞

2.5

–

----------------------------------------

117500

Bus

2.5

–

---------------------------

busth

Bus

()

47000

--------------------------------

1024

-------------

⋅⋅

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