PGA309_05 BURR-BROWN [Burr-Brown Corporation], PGA309_05 Datasheet - Page 15

no-image

PGA309_05

Manufacturer Part Number
PGA309_05
Description
Voltage Output PROFRAMMABLE SENSOR CONDITIONER
Manufacturer
BURR-BROWN [Burr-Brown Corporation]
Datasheet
ADC FOR TEMPERATURE SENSING
The
compensation for the sensor span and offset drift.
Either internal or external temperature sensing is
possible. The temperature can be sensed in one of the
following ways:
D
D
D
The temperature signal is digitized by the onboard
Temp ADC. The output of the Temp ADC is used by the
control digital circuit to read the data from the Lookup
Table in an external EEPROM, and set the output of the
Gain DAC and the Zero DAC to the calibrated values as
temperature changes.
An additional function provided through the Temp ADC
is the ability to read the V
ADC input mux. This provides flexibility for a digital
output through either One-Wire or Two-Wire interface,
as well as the possibility for an external microcontroller
to perform real-time custom calibration of the PGA309.
EXTERNAL EEPROM AND TEMPERATURE
COEFFICIENTS
The PGA309 uses an industry-standard Two-Wire
external EEPROM (typically, a SOT23-5 package). A
1k-bit (minimum) EEPROM is needed when using all 17
temperature coefficients. Larger EEPROMs may be
used to provide space for a serial number, lot code, or
other data.
The first part of the external EEPROM contains the
configuration data for the PGA309, with settings for:
D
D
D
D
This section of the EEPROM contains its own individual
checksum (Checksum1).
The second part of the external EEPROM contains up
to 17 temperature index values and corresponding
temperature coefficients for the Zero DAC and Gain
DAC adjustments with measured temperature, and
also contains its own checksum (Checksum2).
Bridge impedance change (excitation current
sense, in the positive or negative part of the bridge),
for sensors with large temperature coefficient of
resistance (TCR > 0.1%/°C).
On-chip PGA309 temperature, when the chip is
located sufficiently close to the sensor.
External diode, thermistor, or RTD placed on the
sensor membrane. An internal 7µA current source
may be enabled to excite these types of
temperature sensors.
Register 3—Reference Control and Linearization
Register 4—PGA Coarse Offset and Gain/Output
Amplifier Gain
Register 5—PGA Configuration and Over/Under-
Scale Limit
Register 6—Temp ADC Control
www.ti.com
temperature
sense
OUT
pin back through the Temp
circuitry
drives
the
The PGA309 lookup logic contains a linear interpolation
algorithm for accurate DAC adjustments between
stored temperature indexes. This approach allows for
a piecewise linear temperature compensation of up to
17 temperature indexes and associated temperature
coefficients.
If either Checksum1, Checksum2, or both are incorrect,
the output of the PGA309 is set to high-impedance.
FAULT MONITOR
To detect sensor burnout or a short, a set of four
comparators are connected to the inputs of the
Front-End PGA. If any of the inputs are taken to within
100mV of ground or V
the
comparator sets a sensor fault flag that causes the
PGA309 V
or ground, depending upon the alarm configuration
setting
Over/Under-Scale Limit). This will be well above the set
Over-Scale Limit level or well below the set
Under-Scale Limit level. The state of the fault condition
can be read in digital form in Register 8—Alarm Status
Register. If the Over/Under-Scale Limit is disabled, the
PGA309 output voltage will still be driven within 100mV
of either V
configuration setting.
There are five other fault detect comparators that help
detect subtle PGA309 front-end violations that could
otherwise result in linear voltages at V
interpreted as valid states. These are especially useful
during factory calibration and setup, and are configured
through
Over/Under-Scale Limit. Their status can also be read
back through Register 8—Alarm Status Register.
OVER-SCALE AND UNDER-SCALE LIMITS
The over-scale and under-scale limit circuitry combined
with the fault monitor circuitry provides a means for
system diagnostics. A typical sensor-conditioned
output may be scaled for 10% to 90% of the system
ADC range for the sensor normal operating range. If the
conditioned pressure sensor is below 4%, it is
considered under-pressure; if over 96%, it is
considered over-pressure.
The PGA309 over/under-scale limit circuit can be
programmed
over-scale values that clip or limit the PGA309 output.
From a system diagnostic view, 10% to 90% of ADC
range is normal operation, < 4% is under-pressure, and
> 96% is over-pressure. If the fault detect circuitry is
used, a detected fault will cause the PGA309 output to
be driven to positive or negative saturation. If this fault
Front-End
(Register
OUT
Register
SA
SBOS292B − DECEMBER 2003 − REVISED JANUARY 2005
or ground, depending upon the alarm
to be driven within 100mV of either V
individually
PGA,
EXC,
5—PGA
5—PGA
then
or violate the input CMR of
for
Configuration
Configuration
the
under-scale
OUT
corresponding
that would be
PGA309
and
and
and
SA
15

Related parts for PGA309_05