SLYU055A January   2020  – November 2020 TMAG5124

 

  1. 1Trademarks
  2. 2Overview
    1. 2.1 TMAG5124EVM Kit Contents
    2. 2.2 Related Documentation From Texas Instruments
  3. 3Hardware
    1. 3.1 Features
  4. 4Quick Start
    1. 4.1 Option 1: Single 5-V Supply
    2. 4.2 Option 2: Separate VCC and 5-V Supply
    3. 4.3 Measurements
    4. 4.4 Standalone Measurements
  5. 5Circuitry
    1. 5.1 TMAG5124 Coupon Boards
    2. 5.2 Logic, Feedback, and Display
    3. 5.3 J5
  6. 6Schematic, PCB Layout, and Bill of Materials
    1. 6.1 Schematic
    2. 6.2 PCB Layout
    3. 6.3 Bill of Materials
  7. 7Revision History

5.2 Logic, Feedback, and Display

The control board portion of the TMAG5124EVM measures the current in the loop of the TMAG5124, and provides one of three LED feedbacks to the user based on the measured state.

INA303-Q1 is a 36-V common-mode, bidirectional, voltage output current shunt amplifier with integrated window comparator. The device is mainly used here for the window comparator feature, which allows the device to measure three separate states. Current is measured across R1, a precision 3-Ω shunt resistor.

R2, R3, and C10 form a low pass filter for the inputs, as the signal of interest here is mainly a DC signal, and this helps to remove noise on the common mode signal. Note that these resistors have bearing on the gain error of the shunt amplifier, and TI recommends using a value of less than 10 Ω.

R4 and R5 set the limits of the comparator window. The TMAG5124 data sheet explains that for the populated devices, a logic high corresponds to 6 mA, and a logic low corresponds to 12 mA. With this in mind, select resistors using the formula from section 7.3.3.1.1 of the INA303 data sheet:

Equation 2. RLIMIT=ITRIP*RSENSE*GAIN+VREFILIMIT
Equation 3. RLOW=.005*3*2080E-06=3.75kΩ
Equation 4. RHIGH=.015*3*2080E-06=11.25kΩ

Note that for the purposes of error margin, slightly smaller resistance values of 3 kΩ and 10.5 kΩ are used for R4 and R5, respectively.