Datasheet

IOCFG
AINx/GPIOx
ToAnalogMux
DIOWRITE
IODIR
DIOREAD
REFx0/GPIOx
ADS1246
ADS1247
ADS1248
SBAS426G –AUGUST 2008–REVISED OCTOBER 2011 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 or general-purpose digital inputs/outputs
of the actual power supply voltage.
(GPIOs).
Conversion Result = (V
SP
/4)/V
REF
(5)
Figure 65 shows a diagram of how these functions
are combined onto a single pin. Note that when the
Where V
SP
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 = (V
REX
/4)/V
REF
(6)
Where V
REX
is the external reference to be
monitored.
NOTE: The internal reference voltage must be
enabled when measuring an 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 65. Analog/Data Interface Pin
the ADC. Typically, the difference in diode voltage is
118mV at +25°C with a temperature coefficient of
405μV/°C.
SYSTEM MONITOR
Note that when the onboard temperature monitor is
The ADS1247 and ADS1248 provide a system
selected, the PGA is automatically set to '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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