AFE4300 - Weigh Scale / Body Composition Analog Front End

The AFE4300 is a low-cost analog front-end incorporating two separate signal chains: onechain for weight-scale (WS) measurement and the other for body composition measurement (BCM)analysis. A 16-bit, 860-SPS analog-to-digital converter (ADC) is multiplexed between both chains.The weight measurement chain includes an instrumentation amplifier (INA) with the gain set by anexternal resistor, followed by a 6-bit digital-to-analog converter (DAC) for offset correction, anda circuit to drive the external bridge/load cell with a fixed 1.7 V for ratiometricmeasurements.

The AFE4300 can also measure body composition by applying a sinusoidal current into thebody. The sinusoidal current is generated with an internal pattern generator and a 6-bit, 1-MSPSDAC. A voltage-to-current converter applies this sinusoidal current into the body, between twoterminals. The voltage created across these two terminals as a result of the impedance of the bodyis measured back with a differential amplifier, rectified, and the amplitude is extracted andmeasured by the 16-bit ADC.

The AFE4300 operates from 2 V to 3.6 V, is specified from 0°C to +70°C, and is availablein a LQFP-80 package.

• Weight-Scale Front-End:
  • Supports up to Four Load Cell Inputs
  • On-Chip Load Cell 1.7-V Excitation Voltage for Ratiometric Measurement
  • 68-nVrms Input-Referred Noise
    (0.1 Hz to 2 Hz)
  • Best-Fit Linearity: 0.01% of Full-Scale
  • Weight-Scale Measurement : 540 µA
• Body Composition Front-End:
  • Supports Up To Three Tetra-Polar Complex Impedance Measurements
  • 6-Bit, 1-MSPS Sine-Wave Generation Digital-to-Analog Converter (DAC)
  • 247.5-µArms, ±20% Excitation Source
  • 0.1-Ω Measurement RMS Noise in 2-Hz BW
  • Body Composition Measurement : 970 µA
• Analog-to-Digital Converter (ADC):
  • 16 Bits, 860 SPS
  • Supply Current: 110 µA

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