AFE4300 Datasheet, PDF (1/30 Pages) Texas Instruments – Low-Cost, Integrated Analog Front-End for Weight-Scale and Body Composition Measurement

AFE4300
www.ti.com
SBAS586A – JUNE 2012 – REVISED JUNE 2012
Low-Cost, Integrated Analog Front-End
for Weight-Scale and Body Composition Measurement
Check for Samples: AFE4300
FEATURES
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•2 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)
– 375-µArms, ±20% Excitation Source
– Dynamic Range : 0 Ω to 2.8 kΩ
– 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
APPLICATIONS
• Weight Scales with Body Composition
Measurements
DESCRIPTION
The AFE4300 is a low-cost analog front-end
incorporating two separate signal chains: one chain
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 an external
resistor, followed by a 6-bit digital-to-analog converter
(DAC) for offset correction, and a circuit to drive the
external bridge/load cell with a fixed 1.7 V for
ratiometric measurements.
The AFE4300 can also measure body composition by
applying a sinusoidal current into the body. The
sinusoidal current is generated with an internal
pattern generator and a 6-bit, 1-MSPS DAC. A
voltage-to-current converter applies this sinusoidal
current into the body, between two terminals. The
voltage created across these two terminals as a
result of the impedance of the body is measured back
with a differential amplifier, rectified, and its amplitude
is extracted and measured 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 available in a TQFP-80
package.
FUNCTIONAL BLOCK DIAGRAM
INPx
INMx
RG
VLDO
MUX
A1
+
A2
offset
OUTx_FILT
CLK
AVDD
y
Patient
VSENSEPx
&
ESD
VSENSEMx
MUX
A3
Protection
Full Wave
Rectifier
MUX
ADC
(16bit, 860SPS)
SPI
STE
SDIN
SDOUT
SCLK
RDY
IOUTPx
I/Q
Patient
Demodulator
&
Zs
ESD
MUX
Protection
IOUTMx
0.9V
VDAC_FILT_IN
1.5k +/- 20%
VDACOUT
DAC
(6bit)
CLK
DDS
(10bits)
Reference
LDO
AUXx
VREF VLDO
AVSS
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Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
SPI is a trademark of Motorola Inc..
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PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2012, Texas Instruments Incorporated