REF5045 datasheet(31/62 Pages) TI2

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œœ

D17

D16

DOUT-1

& DIN-2

SCLK

CONVST

1/fsample

tACQ

tconv-max

Acquiring

6DPSOH µQ¶

Converting

6DPSOH µQ¶

End-of-

Conversion

ADC

STATE

tconv-min

œœ

$FTXLULQJ 6DPSOH µQ+1¶

ADC 2

GDWD IRU VDPSOH µQ¶

ADC 1

GDWD IRU VDPSOH µQ¶

DOUT-2

œœ

D17

œœ

D17

D16

œœ

D16

DIN-1 = LOW

ADC 1 data

ADC 2 data

ADC 1 data

ADS8881

www.ti.com

SBAS547D – MAY 2013 – REVISED AUGUST 2015

Product Folder Links: ADS8881

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Device Functional Modes (continued)

As shown in Figure 61, the device DOUT pin is driven low when DIN and CONVST are low together. With DIN

low, a CONVST rising edge selects daisy-chain mode, samples the analog input, and causes the device to enter

a conversion phase. In this interface option, CONVST must remain high from the start of the conversion until all

data bits are read. When started, the conversion continues regardless of the state of SCLK, however SCLK must

be low at the CONVST rising edge so that the device does not generate a busy indicator at the end of the

conversion.

Figure 61. Interface Timing Diagram: For Two Devices in Daisy-Chain Mode

At the end of conversion, every ADC in the chain loads its own conversion result into the internal, 18-bit, shift

acquisition phase and power-down. On every subsequent SCLK falling edge, the internal shift register of each

ADC latches the data available on its DIN pin and shifts out the next bit of data on its DOUT pin. Therefore, the

digital host receives the data of ADC N, followed by the data of ADC N–1, and so on (in MSB-first fashion). A

total of 18 x N SCLK falling edges are required to capture the outputs of all N devices in the chain. Fast sampling

rates require high frequency SCLK and data must be read at SCLK falling edges. For slow sampling rates and

SCLK frequency

≤ 36 MHz, data can be read at either SCLK falling or rising edges. Note that with any SCLK

frequency, reading data at SCLK falling edge requires the digital host to clock in the data during the th_CK_DO-min

time frame.

REF5045 Datasheet(PDF) 31 Page - Texas Instruments

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