AD5941 datasheet(32/143 Pages) AD

32 / 143 page

Data Sheet

AD5940/AD5941

LOW POWER DAC

analog.com

Rev. D | 32 of 143

Electrochemical Impedance Spectroscopy

In many electrochemical applications, there is significant value

in carrying out a diagnostic measurement. A typical diagnostic

technique is to carry out an impedance measurement on the

sensor. For some sensor types, the dc bias on the sensor must

be maintained during the impedance measurement. The AD5940/

AD5941 facilitates this dc bias. To perform this measurement, set

LPDACCON0, Bit 5 = 1. VZERO0 voltage is set to the input of the

high speed TIA and the high speed DAC generates an ac signal.

The level of the ac signal is set via the VBIAS0 voltage output of the

low power DAC, and the voltage on SE0 is maintained by VZERO0

voltage. The high speed DAC dc buffers must also be enabled by

setting AFECON, Bit 21.

Low Power DAC in 4-Wire Isolated Impedance

Measurements

For 4-wire isolated impedance measurements, such as body impe-

dance measurements, a high frequency sinusoidal waveform is

applied to the sensor via the high speed DAC. A common-mode

voltage is set across the sensor using the low power DAC 6-bit

output voltage, VZERO, and the low power TIA. This configuration

sets the common-mode voltage between AIN2 and AIN3 (see

Figure 20). To enable this common-mode voltage setup, SWMUX,

Bit 3, must be set to 1. The VBIAS0 voltage output of the low power

DAC also sets the common-mode voltage for the high speed DAC

excitation buffer.

Figure 20. Low Power DACs Used in a 4-Wire Impedance Measurement (HSTIA_P = Positive Output of High Speed TIA)

LOW POWER DAC CIRCUIT REGISTERS

Table 15. Low Power TIA and Low Power DAC Registers Summary

Address

Name

Description

Reset

Access

0x00002128

LPDACCON0

Low power DAC configuration register

0x00000002

R/W

0x00002124

LPDACSW0

Low power DAC switch control register

0x00000000

R/W

0x00002050

LPREFBUFCON

Low power reference configuration register

0x00000000

R/W

0x0000235C

SWMUX

Common-mode switch mux select register

0x00000000

R/W

0x00002120

LPDACDAT0

Low power DAC data output register

0x00000000

R/W

LPDACCON0 Register—LPDACCON0

Address 0x00002128, Reset: 0x00000002, Name: LPDACCON0

Table 16. Bit Descriptions for LPDACCON0 Register

Bits

Bit Name

Settings

Description

Reset

Access

[31:7]

Reserved

Reserved.

0x0

WAVETYPE

Low power DAC data source. This bit determines the DAC waveform type.

0x0

R/W

0 Direct from LPDACDAT0.

1 Waveform generator.

AD5941 Datasheet(PDF) 32 Page - Analog Devices

AD5941 Datasheet(HTML) 32 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL