REF5045 datasheet(25/62 Pages) TI2

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D17

D16

D15

Acquiring

Sample N

Converting

Sample N

Conversion Result of Sample N Clocked-out

while Acquiring Sample N+1

End-of-Conversion

ADC

STATE

DOUT

SCLK

CONVST

1/fsample

tACQ

tconv-max

tconv-min

DIN = HIGH

CONVST = 1

CONVST

SCLK

DOUT

CNV

CLK

SDI

DIN

ADC

Digital Host

DVDD

ADS8881

www.ti.com

SBAS547D – MAY 2013 – REVISED AUGUST 2015

Product Folder Links: ADS8881

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Device Functional Modes (continued)

10.4.1.1 3-Wire CS Mode Without a Busy Indicator

This interface option is most useful when a single ADC is connected to an SPI-compatible digital host. In this

interface option, DIN can be connected to DVDD and CONVST functions as CS (as shown in Figure 50). As

shown in Figure 51, a CONVST rising edge forces DOUT to 3-state, samples the input signal, and causes the

device to enter a conversion phase. Conversion is done with the internal clock and continues regardless of the

state of CONVST. As a result, CONVST (functioning as CS) can be pulled low after the start of the conversion to

select other devices on the board. However, CONVST must return high before the minimum conversion time

(tconv-min) elapses and is held high until the maximum possible conversion time (tconv-max) elapses. A high level on

CONVST at the end of the conversion ensures the device does not generate a busy indicator.

Figure 50. Connection Diagram: 3-Wire CS Mode Without a Busy Indicator (DIN = 1)

Figure 51. Interface Timing Diagram: 3-Wire CS Mode (DIN = 1)

When conversion is complete, the device enters an acquisition phase and powers down. CONVST (functioning

as CS) can be brought low after the maximum conversion time (tconv-max) elapses. On the CONVST falling edge,

DOUT comes out of 3-state and the device outputs the MSB of the data. The lower data bits are output on

subsequent SCLK falling edges. 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. DOUT goes to 3-state after the 18th SCLK falling

edge or when CONVST goes high, whichever occurs first.

REF5045 Datasheet(PDF) 25 Page - Texas Instruments

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