Datasheet

Bridge
Sensor
+VDD
AINP
AINN
VREFN
SW
GND
ADS1131
VREFP
AVDD
Z =500MW
EFF
VREFP VREFN
AVDD
ESD
Protection
C
BUF
Z =500MW
EFF
ADS1131
www.ti.com SBAS449C –JULY 2009–REVISED OCTOBER 2013
VOLTAGE REFERENCE INPUTS LOW-SIDE POWER SWITCH (SW)
(VREFP, VREFN)
The ADS1131 incorporates an internal switch for use
The voltage reference used by the modulator is with an external bridge sensor, as shown in Figure 3.
generated from the voltage difference between The switch can be used in a return path for the bridge
VREFP and VREFN: V
REF
= VREFP – VREFN. The power. By opening the switch, power dissipation in
reference inputs use a structure similar to that of the the bridge is eliminated.
analog inputs. In order to increase the reference input
The switch is controlled by the ADS1131 conversion
impedance, a switching buffer circuitry is used to
status. During normal conversions, the switch is
reduce the input equivalent capacitance. The
closed (the SW pin is connected to GND). During
reference drift and noise impact ADC performance. In
standby or power-down modes, the switch is opened
order to achieve best results, pay close attention to
(the SW pin is high impedance). When using the
the reference noise and drift specifications. A
switch, it is recommended that the negative reference
simplified diagram of the circuitry on the reference
input (VREFN) be connected directly to the bridge
inputs is shown in Figure 2. The switches and
ground terminal, as shown in Figure 3 for best
capacitors can be modeled approximately using an
performance.
effective impedance of:
Figure 2. Simplified Reference Input Circuitry
ESD diodes protect the reference inputs. To prevent
these diodes from turning on, make sure the voltages
Figure 3. Low-Side Power Switch
on the reference pins do not go below GND by more
than 100mV, and likewise, do not exceed AVDD by
100mV:
CLOCK SOURCE
GND – 100mV < (VREFP or VREFN) < AVDD +
The ADS1131 uses an internal oscillator. No external
100mV
clock circuitry is required.
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