5
Current sensing amplifying network
The STEVAL-IPMM10B motor control demonstration board can be configured to run in three-shunt or single-shunt
configurations for field oriented control (FOC).
The current can be sensed thanks to the shunt resistor and amplified by using the on board operational amplifiers
or by the MCU (if equipped with op-amp).
Once the shunt configuration is chosen by setting solder bridge on SW5, SW6, SW7 and SW8 (as described in
Section 4.3.5 Single- or three-shunt selection), the user can choose to send the voltage shunt to the MCU
amplified or unamplified.
Single-shunt configuration requires a single op amp and three-shunt configuration requires three op amps;
therefore, in single-shunt configuration, the only voltage which is sent to the MCU to control the sensing is
connected to phase V through SW2.
SW1, SW2, SW4 can select which signals are sent to micro, as described below:
Table 3.
Op-amp sensing configuration
Symbol
Configuration
Bridge
Sensing
SW1
Single
Shunt
1-2
2-3
open
open
Three
Shunt
1-2
2-3
On-board op-amp
MCU op-amp
SW2
Single
Shunt
1-2
2-3
On-board op-amp
MCU op-amp
Three
Shunt
1-2
2-3
On-board op-amp
MCU op-amp
SW4
Single
Shunt
1-2
2-3
open
open
Three
Shunt
1-2
2-3
On-board op-amp
MCU op-amp
The operational amplifier TSV994 used on amplifying networks has a 20 MHz gain bandwidth and operates with a
single positive supply of 3.3 V.
The amplification network must allow bidirectional current sensing, so that an output offset VO = +1.65 V
represents zero current.
Referencing the
(IOCP = 9.8 A; RSHUNT = 0.08 Ω), the maximum measurable phase current,
considering that the output swings from +1.65 V to +3.3 V (MCU supply voltage) for positive currents and from
+1.65 V to 0 for negative currents is:
(6)
MaxMeasCurrent =
ΔV
rm
= 9.8A
(7)
r
m
=
ΔV
MaxMeasCurrent
=
1.65
9.8
= 0.168Ω
The overall trans-resistance of the two-port network is:
(8)
r
m
= R
SHUNT
⋅ AMP = 0.08 ⋅ AMP = 0.168Ω
(9)
UM2702
Current sensing amplifying network
UM2702
-
Rev 1
page 15/34