User Guide
26 of 44
Revision 1.1
2021-03-21
EVAL-M3-302F User Guide
iMOTION™ Modular Application Design Kit
Hardware description of EVAL-M3-302F
6.1.2
Motor external current feedback configuration and calculation
The shunt resistance R
sh
value can be found in the schematics or User Guide for the power board (for example,
the leg shunt resistors are 30 mΩ for EVAL-M3-CM615PN and 100 mΩ for EVAL-M3-TS6-606).
The current input value is a product of the shunt resistance in milliohms and gain of external current sense
amplifier as shown in Figure 13.
Figure 13
Current shunt feedback and sample timing
Figure 14 depicts IU+ current feedback sensing circuity on EVAL-M3-302F evaluation board. Please note that the
default external amplification gain is less than 1 for current sense in this evaluation board.
Figure 14
The current feedback section on the EVAL-M3-302F evaluation board
Based on the principle of Kirchhoff's voltage law,
𝑉
2
≈ 𝑉
1
≈
(
𝑉
𝐷𝐷
− 𝐼
𝑠ℎ
∗ 𝑅
𝑠ℎ
)
∗
𝑅
23
𝑅
22
+ 𝑅
23
+ 𝐼
𝑠ℎ
∗ 𝑅
𝑠ℎ
=
𝑅
23
𝑅
22
+ 𝑅
23
𝑉
𝐷𝐷
+
𝑅
22
𝑅
22
+ 𝑅
23
𝑅
𝑠ℎ
∗ 𝐼
𝑠ℎ
𝐶𝑢𝑟𝑟𝑒𝑛𝑡 𝑖𝑛𝑝𝑢𝑡 =
𝑅
22
𝑅
22
+ 𝑅
23
𝑅
𝑠ℎ
=
5
6
𝑅
𝑠ℎ
Based on this calculation, and the R
sh
in EVAL-M3-CM615PN is 30 mΩ, the current input for the MADK
combination of EVAL-M3-302F and EVAL-M3-CM615PN is 25 mV/A. Please use same procedure to calculate the
current input for other combinations of MADK boards and enter it into MCEWizard.
