UM0723 datasheet(21/48 Pages) STMICROELECTRONICS

21 / 48 page

UM0723

Board description

Doc ID 15870 Rev 4

21/48

Figure 12.

Three-shunt configuration

For previously mentioned FOC configurations it is necessary to set the proper gain by

applying the W10 jumper and by applying the W11 jumper to the dash marked position.

Six-step (block commutation) current reading configuration

In 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 on the shunt resistor in the same direction, 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 13. In this

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

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

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

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

Equation 5

It is possible to calculate the voltage on the output of the op amp, OP OUT VOUT, as the sum

of a bias, VBIAS, and a signal, VSIGN, component equal to:

Equation 6

Shunt

resistor

Smart SD

VREF

COMPARATOR

VCC

L6390

OPAMP

OPOUT

OP+

CP+

GND

+3.3 V

R3 (R52, R78, R97)

(R53, R75, R99)

R2 (R54, R76, R100)

r (R48, R72, R94)

R (R46, R66, R92)

–

+5 V

–

AM00474

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

OU T

SIGN

BIAS

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