EVAL-AD7612CB Analog Devices Inc, EVAL-AD7612CB Datasheet - Page 27

• Manufacturer Part Number: EVAL-AD7612CB
• Description: BOARD EVALUATION AD7612
• Manufacturer: Analog Devices Inc
• Series: PulSAR®r

Specifications of EVAL-AD7612CB

• Number Of Adc's: 1
• Number Of Bits: 16
• Sampling Rate (per Second): 750k
• Data Interface: Serial, Parallel
• Inputs Per Adc: 1 Single Ended
• Input Range: ±5 V, ±10 V
• Power (typ) @ Conditions: 205mW @ 750kSPS
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD7612
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

SLAVE SERIAL INTERFACE
The pins multiplexed on D[11:4] used for slave serial
interface are: EXT/ INT , INVSCLK, SDIN, SDOUT,
SDCLK and RDERROR.
External Clock (SER/ PAR = High, EXT/ INT = High)
Setting the EXT/ INT = high allows the AD7612 to accept an
externally supplied serial data clock on the SDCLK pin. In this
mode, several methods can be used to read the data. The exter-
nal serial clock is gated by CS . When CS and RD are both low,
the data can be read after each conversion or during the following
conversion. A clock can be either normally high or normally low
when inactive. For detailed timing diagrams, see Figure 42 and
Figure 43.
While the AD7612 is performing a bit decision, it is important
that voltage transients be avoided on digital input/output pins,
or degradation of the conversion result may occur. This is par-
ticularly important during the last 475 ns of the conversion phase
because the AD7612 provides error correction circuitry that can
correct for an improper bit decision made during the first part
of the conversion phase. For this reason, it is recommended that
any external clock provided, is a discontinuous clock that transi-
tions only when BUSY is low, or, more importantly, that it does not
transition during the last 475 ns of BUSY high.
External Discontinuous Clock Data Read After
Conversion
Though the maximum throughput cannot be achieved using
this mode, it is the most recommended of the serial slave modes.
Figure 42 shows the detailed timing diagrams for this method.
After a conversion is complete, indicated by BUSY returning low,
the conversion result can be read while both CS and RD are low.
Data is shifted out MSB first with 16 clock pulses and, depending
on the SDCLK frequency, can be valid on the falling and rising
edges of the clock.
One advantage of this method is that conversion performance is
not degraded because there are no voltage transients on the digital
interface during the conversion process. Another advantage is
the ability to read the data at any speed up to 40 MHz, which
accommodates both the slow digital host interface and the fastest
serial reading.
Daisy-Chain Feature
Also in the read after convert mode, the AD7612 provides a daisy-
chain feature for cascading multiple converters together using
the serial data input, SDIN, pin. This feature is useful for reduce-
ing component count and wiring connections when desired, for
instance, in isolated multiconverter applications. See Figure 42
for the timing details.
An example of the concatenation of two devices is shown in
Figure 41. Simultaneous sampling is possible by using a common
CNVST signal. Note that the SDIN input is latched on the opposite
Rev. 0 | Page 27 of 32
edge of SDCLK used to shift out the data on SDOUT (SDCLK
falling edge when INVSCLK = low). Therefore, the MSB of the
upstream converter follows the LSB of the downstream con-
verter on the next SDCLK cycle. In this mode, the 40 MHz
SDCLK rate cannot be used since the SDIN to SDCLK setup
time, t
SDOUT delay, t
taneously sampled). For proper operation, the SDCLK edge for
latching SDIN (or ½ period of SDCLK) needs to be:
Or the max SDCLK frequency needs to be:
If not using the daisy-chain feature, the SDIN input should be
tied either high or low.
External Clock Data Read During Previous Conversion
Figure 43 shows the detailed timing diagrams for this method.
During a conversion, while both CS and RD are low, the result
of the previous conversion can be read. Data is shifted out MSB
first with 16 clock pulses and, depending on the SDCLK frequency,
can be valid on the falling and rising edges of the clock. The
16 bits have to be read before the current conversion is complete;
otherwise, RDERROR is pulsed high and can be used to interrupt
the host interface to prevent incomplete data reading.
To reduce performance degradation due to digital activity, a fast
discontinuous clock of at least 40 MHz is recommended to ensure
that all the bits are read during the first half of the SAR
conversion phase.
The daisy-chain feature should not be used in this mode since
digital activity occurs during the second half of the SAR
conversion phase likely resulting in performance degradation.
CNVST IN
SCLK IN
t
f
CS IN
Figure 41. Two AD7612 Devices in a Daisy-Chain Configuration
33
1
RDC/SDIN
SDCLK
2 /
, is less than the minimum time specified. (SDCLK to
SDCLK
(UPSTREAM)
AD7612
=
BUSY
#2
=
( 2
32
t
t
, is the same for all converters when simul-
SDOUT
32
CNVST
32
SCLK
1
+
+
CS
t
t
33
33
)
RDC/SDIN
(DOWNSTREAM)
AD7612
BUSY
#1
SDOUT
CNVST
SCLK
CS
AD7612
BUSY
OUT
DATA
OUT