PGA309_05 BURR-BROWN [Burr-Brown Corporation], PGA309_05 Datasheet - Page 13

• Manufacturer Part Number: PGA309_05
• Description: Voltage Output PROFRAMMABLE SENSOR CONDITIONER
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

FUNCTIONAL DESCRIPTION
The PGA309 is a programmable analog signal
conditioner designed for resistive bridge sensor
applications. It is a complete signal conditioner with
bridge excitation, initial span and offset adjustment,
temperature
internal/external temperature measurement capability,
output over-scale and under-scale limiting, fault
detection, and digital calibration. The PGA309, in a
calibrated sensor module, can reduce errors to the level
approaching the bridge sensor repeatability. Figure 1
shows a block diagram of the PGA309. Following is a
brief overview of each major function.
SENSOR ERROR ADJUSTMENT RANGE
The
summarized in Table 1.
Table 1. PGA309 Adjustment Capability
GAIN SCALING
The core of the PGA309 is the precision low-drift and no
1/f noise Front-End PGA. The overall gain of the
Front-End PGA + Output Amplifier can be adjusted
from 2.7V/V to 1152V/V. The polarity of the inputs can
be switched through the 2x2 input mux to accommodate
sensors with unknown polarity output.
The Front-End PGA provides initial coarse signal gain
using a no 1/f noise, auto-zero instrumentation
amplifier. The fine gain adjust is accomplished by the
16-bit attenuating Gain Digital-to-Analog Converter
(Gain DAC). This Gain DAC is controlled by the data in
the Temperature Compensation Lookup Table driven by
the Temperature Analog-to-Digital Converter (Temp
ADC). In order to compensate for second-order and
higher drift nonlinearity, the span drift can be fitted to
FSS (full-scale sensitivity)
Span TC
Span TC nonlinearity
Zero offset
Zero offset TC
Zero offset TC nonlinearity
Sensor impedance
(1) Depends on the temperature sensing scheme
(2) Combined coarse and fine offset adjust
(3) Lower impedance possible by using a dropping resistor in series with the
bridge
www.ti.com
adjustment
adjustment
capability
1mV/V to 245mV/V
Over ±3300ppmFS/°C (1)
> 10%
±200%FS (2)
Over ±3000ppmFS/°C (2)
> 10%
Down to 200Ω (3)
of
of
span
the
and
PGA309
offset,
is
piecewise linear curves during calibration with the
coefficients stored in an external nonvolatile EEPROM
lookup table.
Following the fine gain adjust stage is the Output
Amplifier that provides additional programmable gain.
Two key output amplifier connections, V
brought out on the PGA309 for application flexibility.
These connections allow for an accurate conditioned
signal voltage while also providing a means for PGA309
output overvoltage and large capacitive loading for
RFI/EMI filtering required in many end applications.
OFFSET ADJUSTMENT
The sensor offset adjustment is performed in two
stages. The input-referred Coarse Offset Adjust DAC
has approximately a ±60mV offset adjustment range for
a selected V
are canceled by the 16-bit Zero DAC that sums the
signal with the output of the front-end instrumentation
amplifier. Similar to the Gain DAC, the input digital
values of the Zero DAC are controlled by the data in the
Temperature Compensation Lookup Table, stored in
external EEPROM, driven by the Temp ADC. The
programming range of the Zero DAC is 0V to V
an output range of 0.1V to V
VOLTAGE REFERENCE
The PGA309 contains a precision low-drift voltage
reference (selectable for 2.5V or 4.096V) that can be
used for external circuitry through the REF
pin. This same reference is used for the Coarse Offset
Adjust DAC, Zero DAC, Over/Under-Scale Limits and
sensor excitation/linearization through the V
When
REF
reference or to V
SENSOR EXCITATION AND LINEARIZATION
A dedicated circuit with a 7-bit + sign DAC for sensor
voltage excitation and linearization is provided on the
PGA309. This block scales the reference voltage and
sums it with a portion of the PGA309 output to
compensate the positive or negative bow-shaped
nonlinearity exhibited by many sensors over their
applied pressure range. Sensors not requiring
linearization can be connected directly to the supply
(V
DAC) set to zero.
SA
IN
) or to the V
/REF
the internal reference is disabled, the
SBOS292B − DECEMBER 2003 − REVISED JANUARY 2005
OUT
REF
EXC
of 5V. The fine offset and the offset drift
pin should be connected to an external
SA
for ratiometric-scaled systems.
pin with the Linearization DAC (Lin
SA
− 0.1V.
FB
and V
IN
PGA309
/REF
EXC
REF
SJ
, are
OUT
with
pin.
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