AD7190BRUZ-REEL Analog Devices Inc, AD7190BRUZ-REEL Datasheet - Page 34

• Manufacturer Part Number: AD7190BRUZ-REEL
• Description: 2ch UltraLow Noise 24Bit SD ADC IC.
• Manufacturer: Analog Devices Inc

Specifications of AD7190BRUZ-REEL

• Design Resources: Precision Weigh Scale Design Using AD7190 with Internal PGA (CN0102)
• Number Of Bits: 24
• Sampling Rate (per Second): 4.8k
• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP (0.173", 4.40mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7190
clock source is used, the clock source must be connected to the
MCLK2 pin and the MCLK1 pin must be left floating.
The internal clock can also be made available at the MCLK2
pin. This is useful when several ADCs are used in an application
and the devices need to be synchronized. The internal clock
from one device can be used as the clock source for all ADCs
in the system. Using a common clock, the devices can be syn-
chronized by applying a common reset to all devices, or the
SYNC pin can be pulsed.
BURNOUT CURRENTS
The AD7190 contains two 500 nA constant current generators,
one sourcing current from AV
current from AIN(−) to AGND, where AIN(+) is the positive
analog input terminal and AIN(−) is the negative analog input
terminal in differential mode and AINCOM in pseudo-
differential mode. The currents are switched to the selected
analog input pair. Both currents are either on or off, depending
on the burnout current enable (burn) bit in the configuration
register. These currents can be used to verify that an external
transducer remains operational before attempting to take
measurements on that channel. After the burnout currents are
turned on, they flow in the external transducer circuit, and a
measurement of the input voltage on the analog input channel
can be taken. It will take some time for the burnout currents to
detect an open circuit condition as the currents will need to
charge any external capacitors
There are several reasons why a fault condition can be detected.
The front-end sensor may be open circuit. It could also mean
that the front-end sensor is overloaded, or the reference may be
absent and the NOREF bit in the status register is set, thus
clamping the data to all 1s. The user needs to check these three
cases before making a judgment. If the voltage measured is 0 V,
it may indicate that the transducer has short circuited. The
current sources work over the normal absolute input voltage
range specifications when the analog inputs are buffered and
chop is disabled.
REFERENCE
The ADC has a fully differential input capability for the refer-
ence channel. In addition, the user has the option of selecting
one of two external reference options (REFIN1(x) or REFIN2(x)).
The reference source for the AD7190 is selected using the
REFSEL bit in the configuration register. The REFIN2(x) pins
are dual purpose: they can function as two general-purpose
output pins or as reference pins. When the REFSEL bit is set
to 1, these pins automatically function as reference pins.
The common-mode range for these differential inputs is from
AGND to AV
excessive R-C source impedances introduce gain errors. The
reference voltage REFIN (REFINx(+) − REFINx(−)) is AV
nominal, but the AD7190 is functional with reference voltages
from 1 V to AV
DD
DD
. The reference input is unbuffered; therefore,
. In applications where the excitation (voltage
DD
to AIN(+) and one sinking
DD
Rev. B | Page 34 of 40
or current) for the transducer on the analog input also drives
the reference voltage for the part, the effect of the low frequency
noise in the excitation source is removed because the application is
ratiometric. If the AD7190 is used in a nonratiometric applica-
tion, use a low noise reference.
Recommended 2.5 V reference voltage sources for the AD7190
include the
references. Also note that the reference inputs provide a high
impedance, dynamic load. Because the input impedance of each
reference input is dynamic, resistor/capacitor combinations on
these inputs can cause dc gain errors, depending on the output
impedance of the source driving the reference inputs.
Reference voltage sources like those previously recommended
(for example, ADR431) typically have low output impedances
and are, therefore, tolerant to having decoupling capacitors on
REFINx(+) without introducing gain errors in the system.
Deriving the reference input voltage across an external resistor
means that the reference input sees a significant external source
impedance. External decoupling on the REFINx pins is not
recommended in this type of circuit configuration.
REFERENCE DETECT
The AD7190 includes on-chip circuitry to detect whether the
part has a valid reference for conversions or calibrations. This
feature is enabled when the REFDET bit in the configuration
register is set to 1. If the voltage between the selected REFINx(+)
and REFINx(–) pins is between 0.3 V and 0.6 V, the AD7190
detects that it no longer has a valid reference. In this case, the
NOREF bit of the status register is set to 1. If the AD7190 is
performing normal conversions and the NOREF bit becomes
active, the conversion result is all 1s. Therefore, it is not
necessary to continuously monitor the status of the NOREF bit
when performing conversions. It is only necessary to verify its
status if the conversion result read from the ADC data register
is all 1s. If the AD7190 is performing either an offset or full-
scale calibration and the NOREF bit becomes active, the
updating of the respective calibration registers is inhibited to
avoid loading incorrect coefficients to these registers, and the
ERR bit in the status register is set. If the user is concerned
about verifying that a valid reference is in place every time a
calibration is performed, check the status of the ERR bit at the
end of the calibration cycle.
RESET
The circuitry and serial interface of the AD7190 can be reset
by writing consecutive 1s to the device; 40 consecutive 1s are
required to perform the reset. This resets the logic, the digital
filter, and the analog modulator, whereas all on-chip registers
are reset to their default values. A reset is automatically
performed on power-up. When a reset is initiated, the user
must allow a period of 500 μs before accessing any of the
on-chip registers. A reset is useful if the serial interface loses
synchronization due to noise on the SCLK line.
ADR421
and ADR431, which are low noise