ADS1246IPWR datasheet(21/60 Pages) TI

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Settling Time for Channel Multiplexing

REFN1

REFP1

ADC

ADS1248 Only

REFN0

REFP0

REFN

REFP

VREFCOM

VREFOUT

ReferenceMultiplexer

Internal

Voltage

Reference

VOLTAGE REFERENCE INPUT

ADS1246

ADS1247

ADS1248

www.ti.com .................................................................................................................................................. SBAS426C – AUGUST 2008 – REVISED AUGUST 2009

ESD diodes protect the ADC inputs. To prevent these

As with the analog inputs, REFP0 and REFN0 can be

diodes from turning on, make sure the voltages on

configured as digital I/Os on the ADS1247/48.

the input pins do not go below AVSS by more than

100mV, and do not exceed AVDD by more than

100mV, as shown in Equation 2. Note that the same

caution is true if the inputs are configured to be

GPIOs.

AVSS – 100mV < (AINX) < AVDD + 100mV

(2)

The ADS1246/7/8 is a true single-cycle settling

ΔΣ

converter. The first data available after the start of a

conversion are fully settled and valid for use. The

time required to settle is roughly equal to the inverse

of the data rate. The exact time depends on the

specific data rate and the operation that resulted in

the start of a conversion; see Table 19 for specific

Figure 32. Reference Input Multiplexer

values.

The reference input circuit has ESD diodes to protect

the inputs. To prevent the diodes from turning on,

The voltage reference for the ADS1246/7/8 is the

make sure the voltage on the reference input pin is

differential voltage between REFP and REFN:

not less than AVSS – 100mV, and does not exceed

VREF = VREFP – VREFN

AVDD + 100mV, as shown in Equation 3:

In the case of the ADS1246, these pins are dedicated

AVSS – 100mV < (VREFP or VREFN) < AVDD + 100mV (3)

inputs. For the ADS1247 and ADS1248, there is a

multiplexer that selects the reference inputs, as

shown in Figure 32. The reference input uses a buffer

to increase the input impedance.

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