EVAL-AD7723CBZ Analog Devices Inc, EVAL-AD7723CBZ Datasheet - Page 25

• Manufacturer Part Number: EVAL-AD7723CBZ
• Description: BOARD EVALUATION FOR AD7723
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7723CBZ

• Number Of Adc's: 1
• Number Of Bits: 16
• Sampling Rate (per Second): 1.2M
• Data Interface: Serial, Parallel
• Inputs Per Adc: 1 Differential
• Input Range: ±VREF
• Power (typ) @ Conditions: 475mW @ 1.2MSPS
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD7723
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

SERIAL INTERFACE
The AD7723’s serial data interface can operate in three modes,
depending on the application requirements. The timing
diagrams in Figure 4, Figure 5, and Figure 6 show how the
AD7723 may be used to transmit its conversion results. Table 3
shows the control inputs required to select each serial mode and
the digital filter operating mode. The AD7723 operates solely in
the master mode, providing three serial data output pins for
transfer of the conversion results. The serial data clock output,
SCO, serial data output, SDO, and frame sync output, FSO, are
all synchronous with CLKIN. FSO is continuously output at the
conversion rate of the ADC.
Serial data shifts out of the SDO pin synchronous with SCO.
The FSO is used to frame the output data transmission to an
external device. An output data transmission is either 16 or 32
SCO cycles in duration (see Table 3). Serial data shifts out of the
SDO pin, MSB first, LSB last, for a duration of 16 SCO cycles. In
Serial Mode 1, SDO outputs 0s for the last 16 SCO cycles of the
32-cycle data transmission frame.
The clock format pin, CFMT, selects the active edge of SCO.
With CFMT tied logic low, the serial interface outputs FSO and
SDO change state on the SCO rising edge and are valid on the
falling edge of SCO. With CFMT set high, FSO and SDO
change state on the falling SCO edge and are valid on the SCO
rising edge.
The frame sync input, FSI, can be used if the AD7723
conversion process must be synchronized to an external source.
FSI allows the conversion data presented to the serial interface
to be a filtered and decimated result derived from a known
point in time. A common frame sync signal can be applied to
two or more AD7723s to synchronize them to a common
master clock.
When FSI is applied for the first time, the digital filter
sequencer counter is reset to 0, the AD7723 interrupts the
current data transmission, reloads the output shift register,
resets SCO, and transmits the conversion result. Synchro-
nization starts immediately and the following conversions are
invalid while the digital filter settles. FSI can be applied once
after power-up, or it can be a periodic signal, synchronous to
CLKIN, occurring every 32 CLKIN cycles. Subsequent FSI
inputs applied every 32 CLKIN cycles do not alter the serial
data transmission and do not reset the digital filter sequencer
counter. FSI is an optional signal; if synchronization is not
required, FSI can be tied to a logic low and the AD7723
generates FSO outputs.
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In Serial Mode 1, the control input, SFMT, can be used to select
the format for the serial data transmission (see Figure 4). FSO is
either a pulse, approximately one SCO cycle in duration, or a
square wave with a period of 32 SCO cycles. With a logic low
level on SFMT, FSO pulses high for one SCO cycle at the
beginning of a data transmission frame. With a logic high level
on SFMT, FSO goes low at the beginning of a data transmission
frame and returns high after 16 SCO cycles.
Note that in Serial Mode 1, FSI can be used to synchronize the
AD7723 if SFMT is set to a logic high. If SFMT is set low, the
FSI input has no effect on synchronization.
In Serial Mode 2 and Serial Mode 3, SFMT should be tied high.
TSI and DOE should be tied low in these modes. The FSO is a
pulse, approximately one SCO cycle in duration, occurring at
the beginning of the serial data transmission.
TWO-CHANNEL MULTIPLEXED OPERATION
Two additional serial interface control pins, DOE and TSI, are
provided to allow the serial data outputs of two AD7723s, to
easily share one serial data line when operating in Serial
Mode 1. Figure 45 shows the connection diagram. Since a serial
data transmission frame lasts 32 SCO cycles, two ADCs can
share a single data line by alternating transmission of their 16-
bit output data onto one SDO pin.
The data output enable pin, DOE, controls the SDO output
buffer. When the logic level on DOE matches the state of the
TSI pin, the SDO output buffer drives the serial data line;
otherwise, the output of the buffer goes high impedance. The
serial format pin, SFMT, is set high to choose the frame sync
output format. The clock format pin, CFMT, is set low so that
serial data is made available on SDO after the rising edge of
SCO and can be latched on the SCO falling edge.
Figure 45. Serial Mode 1 Connection for Two-Channel Multiplexed Operation
DV
DGND
DGND
DD
DV
DD
SFMT
CFMT
TSI
FSI
CLKIN
FSI
CLKIN
SFMT
TSI
CFMT
AD7723
AD7723
MASTER
SLAVE
SDO
SCO
DOE
DOE
SDO
SCO
FSO
FSO
TO HOST
PROCESSOR
FROM
CONTROL
LOGIC
AD7723