UM0900 datasheet(19/43 Pages) STMICROELECTRONICS

19 / 43 page

UM0900

Board description

Doc ID 17028 Rev 1

19/43

Figure 10.

Three-shunt configuration

Six-step (block commutation) current reading configuration

In the case of six-step (also called block commutation) current control, only two of the motor

phases conduct current at the same time. Therefore, it is possible to use only one shunt

resistor placed on the DC link to measure the motor phase current. Moreover, as the current

is always flowing in the same direction on the shunt resistor, only positive current must be

measured and in this case the amplifying network needs to be properly designed. The

details of single-shunt current sensing reading configuration are shown in Figure 11. In this

configuration, the current sampling is done only when the value on the shunt resistor is

positive. Only the positive value read on the shunt resistor allows the setting of a higher gain

for the op-amp than the one set in three-shunt reading mode.

The op-amp is used in follower mode with gain of the op-amp set by resistor r and R:

Equation 5

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