AD7770 datasheet(49/94 Pages) AD

49 / 94 page

Data Sheet

AD7770

Rev. A | Page 49 of 94

SAR DRIVER

CONTROL LOGIC

FIFO

ON-CHIP

DIAGNOSTICS

SPI

AUXAIN+

AUXAIN–

AVDD4

AVSS4

CONVST_SAR

MUX

DEGLITCH

SAR ADC

REF

Figure 105. SAR ADC Configuration and Control

Table 31. Σ-Δ Diagnostic

Input

Voltage

Recommended Voltage Reference

Notes/Result

Floating

Not applicable

Floating

Not applicable

280 mV differential signal

Internal/external

PGA gain calibration

External reference, positive/negative

External

Positive full scale

External reference, negative/positive

External

Negative full scale

External reference, negative/negative

External

Zero scale

Internal reference, positive/negative

Internal

Positive full scale

Internal reference, negative/positive

Internal

Negative full scale

Internal reference, positive/positive

Internal

Zero scale

External reference, positive/positive

External

Zero scale

Σ-Δ ADC DIAGNOSTICS (SPI CONTROL MODE)

The AD7770 Σ-Δ ADC diagnostic functions are accessible

through the SPI. The internal mux placed before the PGA has

different inputs, allowing the user to select a zero-scale, positive

full-scale, or negative full-scale input to the Σ-Δ ADC, which

can be converted to verify the correct operation of the

Σ-Δ ADC channel.

The diagnostic mux control signals are shared across all the Σ-Δ

channels. Depending on the diagnostic selected, connect the

Σ-Δ ADC reference to a different reference source to guarantee

that the conversion is within the measurable range.

There are two different ways to enable the diagnostic mux, as

follows:



Setting the CHx_RX bit. This bit enables the input Σ-Δ

mux. The multiplexer inputs are described in Table 31. The

reference used during the conversions are controlled by the

REF_MUX_CTRL bits.



Setting CHx_REF_MONITOR. This bit has the same effect

as enabling the CHx_RX bit and selects the VDD1x/AVSSx

supplies as the main reference.

If the AINx± pin is connected to AVSSx, the input range is

outside the range of AVSSx + 100 mV; therefore, results may

differ slightly from the expected value.

Alternatively, the inputs can be used to calibrate gain and offset

errors.

AD7770 Datasheet(PDF) 49 Page - Analog Devices

AD7770 Datasheet(HTML) 49 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

Datasheet Download

Link URL