AD7890BNZ-2 Analog Devices Inc, AD7890BNZ-2 Datasheet - Page 22

• Manufacturer Part Number: AD7890BNZ-2
• Description: IC,Data Acquisition System,8-CHANNEL,12-BIT,DIP,24PIN,PLASTIC
• Manufacturer: Analog Devices Inc
• Type: Data Acquisition System (DAS)r

Specifications of AD7890BNZ-2

• Resolution (bits): 12 b
• Sampling Rate (per Second): 117k
• Data Interface: Serial
• Voltage Supply Source: Single Supply
• Voltage - Supply: 0 V ~ 2.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 24-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7890
In the scheme outlined here, the user does not have to worry
about monitoring the end of conversion. Once conversion is
complete, the AD7890 takes care of transmitting back its
conversion result to the processor. Once the 16 bits of data have
been received by the processor into its serial shift register, it
generates an internal interrupt. Since the RFS pin and the TFS
pin are connected together, data is transmitted to the control
register of the AD7890 whenever the AD7890 transmits its
conversion result. The user just has to ensure that the word to
be written to the AD7890 control register is set up prior to the
end of conversion. As part of the interrupt routine, which
recognizes that data has been read in, the processor can set up
the data it is going to write to the control register next time around.
TMS320C25/C30
Figure 18. AD7890 to TMS320C25/30 Interface
CLKR
CLKX
FSR
FSX
DR
DX
SMODE
RFS
TFS
SCLK
DATA OUT
DATA IN
CLK INPUT
AD7890
CLK IN
Rev. C | Page 22 of 28
ANTIALIASING FILTER
The AD7890 provides separate access to the multiplexer and
ADC via the MUX OUT pin and the SHA IN pin. One of the
reasons for this is to allow the user to implement an antialiasing
filter between the multiplexer and the ADC. Inserting the
antialiasing filter at this point has the advantage that one
antialiasing filter can suffice for all eight channels rather than a
separate antialiasing filter for each channel if they were to be
placed prior to the multiplexer.
The antialiasing filter inserted between the MUX OUT pin and
the SHA IN pin is generally a low-pass filter to remove high
frequency signals which could possibly be aliased back in-band
during the sampling process. It is recommended that this filter
is an active filter, ideally with the MUX OUT pin of the AD7890
driving a high impedance stage and the SHA IN pin of the part
being driven from a low impedance stage. This removes any
effects from the variation of the part’s multiplexer on-resistance
with input signal voltage, and removes any effects of a high
source impedance at the sampling input of the track/hold. With
an external antialiasing filter in place, the additional settling
time associated with the filter should be accounted for by using
a larger capacitance on C
EXT
.