UM1036
Board description
Doc ID 18293 Rev 1
19/48
Configuration with a shunt resistor, where voltage amplified with an operational amplifier is
sensed, was chosen as current sensing networks. Single-shunt configuration requires
a single op amp, three-shunt configuration requires three op amps. For compatibility
purposes, one of them is common to both basic configurations.
The configuration jumpers W11, W12, W13, and W14 allow to set the common op amp to
achieve compatibility between single-shunt six-step configuration (suitable for scalar control)
and three-shunt or single-shunt FOC current reading configuration. The operational
amplifier TSV994 used on amplifying networks has a 20 MHz gain bandwidth and operates
with just a single positive supply of +5 V.
Three-shunt FOC or single-shunt FOC current reading configuration
Details of the FOC current-sensing reading configuration are shown in
Figure 11
. In this
configuration, the alternating signal on the shunt resistor, with positive and negative values,
must be converted to be compatible with the single positive input of the microcontroller A-D
converter used to read the current value.
The op amp is used in symmetrical follower mode: its gain is set by resistors r and R:
Equation 2
It is possible to calculate the voltage on the output of the op amp OP OUT -
V
OUT
as a sum
of a bias
V
BIAS
and a signal
V
SIGN
component equal to:
Equation 3
Total gain of the circuit including the resistor divider is equal to:
Equation 4
r
r1
R
+
L S
(
)
r2
×
r1
R
LS
r2
+
+
----------------------------------------
=
G
R
r
+
r
------------
=
V
OU T
V
SIGN
V
BIAS
+
=
V
BI AS
3.3
1
R1
--------
1
R2
--------
1
R3
--------
+
+
⎝
⎠
⎛
⎞
R3
×
----------------------------------------------------------
G
×
=
V
SIGN
I
R
HS
×
1
R1
--------
1
R2
--------
1
R3
--------
+
+
⎝
⎠
⎛
⎞
R1
×
----------------------------------------------------------
G
×
=
G
TOT
V
SIGN
V
IN
----------------
V
SI GN
R
H S
I
×
--------------------
=
=
