````

OPAMP1

DDS

R1

DAC 6bit

1MSPS

2

150KHz

LPF

R

R

2R

2R

External clock

REF

100K

100k

80k

80k

80k, 160k, 240k, 320k

80k, 160k, 240k, 320k

Current

DAC 6bit

VREF

+/-

6.5uA

A+

A-

BODY COMPOSITION METER

WEIGHT SCALE

ADC_REF_SEL

16[6:5]

PERIPHERAL_SEL

16[4:0]

5

5K

I/Q DEMODULATOR

OR

FULL-WAVE RECTIFIER

I

Q

Clock

Divider

1

0

WS_PDB

9[0]

BCM_PDB

9[1]

DAC_PD

9[3]

1

ISW_MUX

10[15:0]

VSW_MUX

11[15:0]

1

IQ_MODE_ENABLE

12[11]

IQ_DEMOD_CLK_DIV_FAC

15[13:11]

I/Q_DEMOD_CLK

WS_PGA_GAIN

13[14:13]

OFFSET_DAC_VALUE

13[5:0]

BCM_DAC_FREQ

14[9:0]

1

AVDD

LDO

AUX2

AUX1

BAT_MON_EN

15[0], 15[7]

1

0

BRIDGE_SEL

15[2:1]

BRIDGE_SEL

15[2:1]

11001

10001

01001

00000

00101

00011

AVSS

A1

A2

ADC_MEAS_MODE

1[13:11]

3

External clock

ADC

16b 860sps

ADC

REF

Clock

Divider

(

ADC_DATA_RATE

1[6:4]

16

3

1

ADC_PD

1[7]

1

ADC_CONV_MODE

1[15]

SPI

ADC_DATA_RESULT

0[15:0]

000

001

010

PDB

9[2]

D

e

c

im

a

tio

n

F

ilte

r

AVDD

VLDO

1

0

VLDO

5K

5K

5K

0.9V

1.5k +/- 15%

IOUT5

IOUT4

IOUT3

IOUT2

IOUT1

IOUT0

RP1

RP0

RN1

RN0

VSENSE5

VSENSE4

VSENSE3

VSENSE2

VSENSE1

VSENSE0

VSENSERP1

VSENSERP0

VSENSERN1

VSENSERN0

Decimation

Filter

INP_R

INM_R

optional

10uF

10uF

AFE4300

SBAS586A – JUNE 2012 – REVISED JUNE 2012

www.ti.com

OVERVIEW

The AFE4300 is a low-cost, integrated front-end designed for weight scales incorporating body-composition

measurements. The AFE4300 integrates all the components typically used in a weight scale. It has two signal

chains: one for weight scale measurements and the other for body composition measurements. Both signal

chains share a 16-bit, delta-sigma converter that operates at a data rate of up to 860 SPS. This device also

integrates a reference and a low-dropout regulator (LDO) that generates a 1.7-V supply that can be used as the

excitation source for the load cells, thus simplifying ratiometric measurements. Both the signal chains use a

single DAC. The DAC is used to generate the dc signal for load-cell offset cancellation in the weight-scale chain.

The same DAC is also used to generate the sine-wave modulation signal for the body-composition signal chain.

Therefore, only one of the two signal chains can be activated at a time (using the apprpriate register bits).

Two unique features of the AFE4300 are that it provides an option for connecting up to four separate load cells,

and supports tetrapolar measurements with I/Q measurements.

Figure 6. Block Diagram

10

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Product Folder Link(s): AFE4300