ADS1246 datasheet(30/66 Pages) TI

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IOCFG

AINx/GPIOx

ToAnalogMux

DIOWRITE

IODIR

DIOREAD

REFx0/GPIOx

ADS1246

ADS1247

ADS1248

SBAS426D – AUGUST 2008 – REVISED MARCH 2010

www.ti.com

Power-Supply Monitor

GENERAL-PURPOSE DIGITAL I/O

The system monitor can measure the analog or

The ADS1248 has eight pins and the ADS1247 has

digital power supply. When measuring the power

four pins that serve a dual purpose as either analog

supply, the resulting conversion is approximately 1/4

inputs

general-purpose

digital

inputs/outputs

of the actual power supply voltage.

(GPIOs).

Conversion Result = (VSP/4)/VREF

(5)

Figure 62 shows a diagram of how these functions

are combined onto a single pin. Note that when the

Where VSP is the selected supply to be measured.

pin is configured as a GPIO, the corresponding logic

is powered from AVDD and AVSS. When the

External Voltage Reference Monitor

ADS1247/8

are

operated

with

bipolar

analog

The ADS1246/7/8 can be selected to measure the

supplies, the GPIO outputs bipolar voltages. Care

external voltage reference. In this configuration, the

must be taken loading the GPIO pins when used as

monitored external voltage reference is connected to

outputs because large currents can cause droop or

the analog input. The result (conversion code) is

noise on the analog supplies.

approximately 1/4 of the actual reference voltage.

Conversion Result = (VREX/4)/VREF

(6)

Where

VREX is the external reference to be

monitored.

NOTE: The internal reference voltage must be

enabled

when

measuring

external

voltage

reference using the system monitor.

Ambient Temperature Monitor

On-chip

diodes

provide

temperature-sensing

capability. When selecting the temperature monitor

function, the anodes of two diodes are connected to

Figure 62. Analog/Data Interface Pin

the ADC. Typically, the difference in diode voltage is

118mV at +25°C with a temperature coefficient of

405mV/°C.

SYSTEM MONITOR

Note that when the onboard temperature monitor is

The ADS1247 and ADS1248 provide a system

selected,

the

PGA

automatically

set

'1'.

monitor function. This function can measure the

However, the PGA register bits in are not affected

analog power supply, digital power supply, external

and the PGA returns to its set value when the

voltage reference, or ambient temperature. Note that

temperature monitor is turned off.

the system monitor function provides a coarse result.

When the system monitor is enabled, the analog

inputs are disconnected.

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