AD7985 Analog Devices, AD7985 Datasheet - Page 18

• Manufacturer Part Number: AD7985
• Description: 16-Bit, 2.5 MSPS PulSAR 11 mW ADC in QFN
• Manufacturer: Analog Devices

Specifications of AD7985

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 2.5MSPS
• Interface: Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: (Vref) p-p,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: CSP

AD7985
DATA READING OPTIONS
There are three different data reading options for the AD7985.
There is the option to read during conversion, to split the read
across acquisition and conversion (see Figure 28 and Figure 29),
and, in normal mode, to read during acquisition. The desired
SCK frequency largely determines which reading option to use.
Reading During Conversion, Fast Host (Turbo or
Normal Mode)
When reading during conversion (n), conversion results are for
the previous (n − 1) conversion. Reading should occur only up
to t
fast SCK.
The required SCK frequency is calculated by
To determine the minimum SCK frequency, follow these
examples to read data from conversion (n − 1).
For turbo mode (2.5 MSPS):
For normal mode (2.0 MSPS):
The time between t
which digital activity should not occur, or sensitive bit decisions
may be corrupted.
Split-Reading, Any Speed Host (Turbo or Normal Mode)
To allow for a slower SCK, there is the option of a split read,
where data access starts at the current acquisition (n) and spans
into the conversion (n). Conversion results are for the previous
(n − 1) conversion.
Similar to reading during conversion, split-reading should
occur only up to t
only time restriction is that split-reading take place during the
t
falling edge of SCK and CNV rising is an acquisition quiet
time, t
ACQ
DATA
(minimum) + (t
Number_SCK_Edges = 16; t
f
Number_SCK_Edges = 16; t
f
SCK
SCK
f
SCK
QUIET
and, because this time is limited, the host must use a
= 16/190 ns = 84.2 MHz
= 16/290 ns = 55.2 MHz
≥
.
Number
DATA
DATA
DATA
t
. For the maximum throughput, the
_
DATA
SCK
and t
− t
QUIET
_
CONV
Edges
) time. The time between the
DATA
DATA
is an I/O quiet time during
= 190 ns
= 290 ns
Rev. A | Page 18 of 28
To determine how to split the read for a particular SCK frequency,
follow these examples to read data from conversion (n − 1).
For turbo mode (2.5 MSPS):
Thirteen bits are read during conversion (n), and three bits are
read during acquisition (n).
For normal mode (2.0 MSPS):
Thirteen bits are read during conversion (n), and three bits are
read during acquisition (n).
For slow throughputs, the time restriction is dictated by the
throughput required by the user; the host is free to run at any
speed. Similar to reading during acquisition, data access for
slow hosts must take place during the acquisition phase with
additional time into the conversion.
Note that data access spanning conversion requires the CNV
pin to be driven high to initiate a new conversion, and data
access is not allowed when CNV is high. Thus, the host must
perform two bursts of data access when using this method.
Reading During Acquisition, Any Speed Host (Turbo or
Normal Mode)
When reading during acquisition (n), conversion results are
for the previous (n − 1) conversion. Maximum throughput is
achievable in normal mode (2.0 MSPS); however, in turbo
mode, 2.5 MSPS throughput is not achievable.
For the maximum throughput, the only time restriction is that
reading take place during the t
throughputs, the time restriction is dictated by the throughput
required by the user; the host is free to run at any speed. Thus,
for slow hosts, data access must take place during the acquisi-
tion phase.
f
Number_SCK_Edges = 70 MHz × 190 ns = 13.3
f
Number_SCK_Edges = 45 MHz × 290 ns = 13.05
SCK
SCK
= 70 MHz; t
= 45 MHz; t
DATA
DATA
= 190 ns
= 290 ns
ACQ
(minimum) time. For slow