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1/2 channel 4-20 mA to voltage converter boards using LMP8640 current sense monitor.

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2ch-4-20mA-converter

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This board converts two 4 - 20 mA signals to a voltage using a LMP8640 Current Shunt Monitor from Texas Instruments. To provide power to the 4 - 20 mA sensors a TEC2-0913 2W 15V Isolated DC-DC converter is used from Traco Power. Quick-connect terminals from Phoenix Contact are also used.

To allow for extensive testing three separate GND nets/planes and a lot of test points are used. They can be connected together using jumpers if necessary. The power supply can also be disabled and fully disconnected from the sensors using a jumper as well (wich can also be used to measure the in-line current given to the whole sensor circuit).

  • Click here to go to the schematic.

PCB front           PCB back


LMP8640 vs INA196

A lot of designs still use the INA196 Current Shunt Monitor from Texas Instruments. In the picture below is a comparison between the LMP8640 and the INA196. No real disadvantage was found to not use the LMP8640.


PCB front


BOM

Component Value Footprint Other Ordering
U1, U2 LMP8640 SOT-23-Thin-6 Texas Instruments Current Shunt Monitor Mouser.be
U3 TEC2-0913 SIP-8 Traco Power 2W 15V Isolated DC-DC converter Mouser.be
C1, C2 100 nF = 0,1 µF 0805 X7R, 16V, 10% Mouser.be
R1, R2 6,2 Ω 0805 0,1% Mouser.be
R1, R2 (alt) 4,99 Ω 0805 0,1% Mouser.be
J1, J2 PTSA_1,5/_2-3,5-Z_BK Pitch: 3,5 mm 2 contacts @ 45° (20-16 AWG), 250V 2A Mouser.be

UPDATE 03/2020 - 1 CH board without power supply

To better conduct tests with the LMP8640 chip a simple 1-CH board was layed out without a power supply and etched on a single sided board.

  • Click here to go to the schematic.
  • Click here to go to the board layout (mirrored).