AD7190
Temp (K) = (Conversion – 0x800000)/2815 K
Temp (°C) = Temp (K) – 273
SYSTEM SYNCHRONIZATION
SYNC
The
input allows the user to reset the modulator and the
digital filter without affecting any of the setup conditions on the
part. This allows the user to start gathering samples of the analog
input from a known point in time, that is, the rising edge of
Following the one point calibration, the internal temperature
sensor has an accuracy of 2 °C, typically.
BRIDGE POWER-DOWN SWITCH
SYNC SYNC
.
needs to be taken low for four master clock cycles
In bridge applications such as strain gauges and load cells, the
bridge itself consumes the majority of the current in the system.
For example, a 350 Ω load cell requires 15 mA of current when
excited with a 5 V supply. To minimize the current consumption
of the system, the bridge can be disconnected (when it is not
being used) using the bridge power-down switch. Figure 18
shows how the bridge power-down switch is used. The switch
can withstand 30 mA of continuous current, and it has an on
resistance of 10 Ω maximum.
to implement the synchronization function.
If multiple AD7190 devices are operated from a common master
clock, they can be synchronized so that their data registers are
SYNC
updated simultaneously. A falling edge on the
the digital filter and the analog modulator and places the AD7190
SYNC
pin resets
into a consistent, known state. While the
AD7190 is maintained in this state. On the
pin is low, the
SYNC
rising edge,
the modulator and filter are taken out of this reset state and, on
the next clock edge, the part starts to gather input samples again.
In a system using multiple AD7190 devices, a common signal to
LOGIC OUTPUTS
The AD7190 has four general-purpose digital outputs, P0, P1,
P2, and P3. These are enabled using the GP32EN and GP10EN
bits in the GPOCON register. The pins can be pulled high or
low using the P0DAT to P3DAT bits in the GPOCON register;
that is, the value at the pin is determined by the setting of the
P0DAT to P3DAT bits. The logic levels for these pins are
determined by AVDD rather than by DVDD. When the GPOCON
register is read, the bits P0DAT to P3DAT reflect the actual
value at the pins. This is useful for short-circuit detection.
SYNC
their
pins synchronizes their operation. This is normally
done after each AD7190 has performed its own calibration or
has had calibration coefficients loaded into its calibration
registers. The conversions from the AD7190s are then
synchronized.
The part is taken out of reset on the master clock falling edge
following the
multiple devices are being synchronized, the
be taken high on the master clock rising edge to ensure that all
devices begin sampling on the master clock falling edge. If the
SYNC
low to high transition. Therefore, when
SYNC
pin should
These pins can be used to drive external circuitry, for example,
an external multiplexer. If an external multiplexer is used to
increase the channel count, the multiplexer logic pins can be
controlled via the AD7190 general-purpose output pins. The
general-purpose output pins can be used to select the active
multiplexer pin. Because the operation of the multiplexer is
independent of the AD7190, the AD7190 modulator and filter
SYNC
pin is not taken high in sufficient time, it is possible to
have a difference of one master clock cycle between the devices;
that is, the instant at which conversions are available differs
from part to part by a maximum of one master clock cycle.
SYNC
The
In this mode, the rising edge of
RDY
pin can also be used as a start conversion command.
SYNC
starts conversion, and the
indicates when the conversion is complete.
SYNC
should be reset using the
pin each time that the multi-
falling edge of
plexer channel is changed.
The disadvantage of this scheme is that the settling time of the
filter has to be allowed for each data register update. This means
that the rate at which the data register is updated is reduced. For
example, if the ADC is configured to use the sinc4 filter, zero
latency is disabled and chop is disabled, the data register update
takes four times longer.
ENABLE PARITY
The AD7190 also has a parity check function on-chip that
detects 1-bit errors in the serial communications between the
ADC and the microprocessor. When the ENPAR bit in the
mode register is set to 1, parity is enabled. The contents of the
status register must be transmitted along with each 24-bit
conversion when the parity function is enabled. To append the
contents of the status register to each conversion read, the
DAT_STA bit in the mode register should be set to 1. For each
conversion read, the parity bit in the status register is
programmed so that the overall number of 1s transmitted in the
24-bit data-word is even. Therefore, for example, if the 24-bit
conversion contains eleven 1s (binary format), the parity bit is
set to 1 so that the total number of 1s in the serial transmission is
even. If the microprocessor receives an odd number of 1s, it
knows that the data received has been corrupted.
TEMPERATURE SENSOR
Embedded in the AD7190 is a temperature sensor. This is
selected using the CH2 bit in the configuration register. When
the CH2 bit is set to 1, the temperature sensor is enabled. When
the temperature sensor is selected and bipolar mode is selected,
the device should return a code of 0x800000 when the temper-
ature is 0 K. A one-point calibration is needed to get the opti-
mum performance from the sensor. Therefore, a conversion at a
known temperature should be recorded. Using this point along
with the 0 K point, the gain error can be calculated. The
sensitivity is 2815 codes/°C, typically. The equation for the
temperature sensor is
Rev. 0 | Page 3± of 40
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