ADS1258IPHPREP datasheet(28/57 Pages) TI

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DRDY

SCLK

DRDY with SCLK

DRDY without SCLK

DRDYPLS

DRDYPLS =

CLK

ADS1258-EP

SBAS445C – MARCH 2009 – REVISED DECEMBER 2009

www.ti.com

Data Ready Output (DRDY)

DRDY is usually connected to an interrupt of a

controller, DSP, or connected to a controller port pin

The DRDY pin is an output that asserts low to

for polling in a software loop. Channel data can be

indicate when new channel data is available to read

read without the use of DRDY. Read the data using

(the previous conversion data is lost). DRDY returns

the register format read and check the Status Byte

high after the first falling edge of SCLK during a data

when the NEW bit = 1, which indicates new channel

read operation. If the data is not read (no SCLK

data.

pulses), DRDY remains low until new channel data is

available once again. DRDY then pulses high, then

Output Data Scaling and Over-Range

low to indicate new data is available; see Figure 53.

The ADS1258 is scaled such that the output data

code resulting from an input voltage equal to ±VREF

has

margin

6.6%

before

clipping.

This

architecture allows operation of applied input signals

at or near full-scale without overloading the converter.

Specifically, the device is calibrated so that:

1LSB = VREF/780000h,

and the output clips when:

|VIN| ≥ 1.06 × VREF.

Table 8 summarizes the ideal output codes versus

input signals.

Figure 53. DRDY Timing

(See Figure 2 for the DRDY Pulse)

Table 8. Ideal Output Code vs Input Signal

INPUT SIGNAL VIN

(ADCINP – ADCINN)

IDEAL OUTPUT CODE(1)

DESCRIPTION

≥ +1.06 VREF

7FFFFFh

Maximum Positive Full-Scale Before Output Clipping

+VREF

780000h

VIN = +VREF

+1.06 VREF/(2

23 – 1)

000001h

+1LSB

000000h

Bipolar Zero

–1.06 VREF/(2

23 – 1)

FFFFFFh

–1LSB

–VREF

87FFFFh

VIN = –VREF

≤ –1.06 VREF × (2

23/223 – 1)

800000h

Maximum Negative Full-Scale Before Output Clipping

(1)

Excludes effects of noise, linearity, offset, and gain errors.

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ADS1258IPHPREP Datasheet(PDF) 28 Page - Texas Instruments

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