EVAL-AD7689EDZ Datasheet, PDF (30/32 Pages) Analog Devices – 16-Bit, 4-Channel/8-Channel, 250 kSPS PulSAR ADC

AD7682/AD7689
Data Sheet
READ/WRITE SPANNING CONVERSION WITH A
BUSY INDICATOR
This mode is used when the AD7682/AD7689 are connected to
any host using an SPI, serial port, or FPGA with an interrupt
input. The connection diagram is shown in Figure 42, and the
corresponding timing is given in Figure 43. For the SPI, the
host should use CPHA = CPOL = 1. Reading/writing spanning
conversion is shown, which covers all three modes detailed in
the Digital Interface section.
A rising edge on CNV initiates a conversion, ignores data
present on DIN and forces SDO to high impedance. After the
conversion is initiated, it continues until completion irrespec-
tive of the state of CNV. CNV must be returned low before the
safe data transfer time, tDATA, and then held low beyond the
conversion time, tCONV, to generate the busy signal indicator.
When the conversion is complete, SDO transitions from high
impedance to low (data ready), and with a pull-up to VIO, SDO
can be used to interrupt the host to begin data transfer.
After the conversion is complete, the AD7682/AD7689 enter
the acquisition phase and power-down. The host must enable
the MSB of the CFG register at this time (if necessary) to begin
VIO
AD7682/
AD7689
SDO
CNV
DIN
SCK
the CFG update. While CNV is low, both a CFG update and a
data readback take place. The first 14 SCK rising edges are used to
update the CFG register, and the first 16 SCK falling edges clock
out the conversion results starting with the MSB. The restric-
tion for both configuring and reading is that they both occur
before the tDATA time elapses for the next conversion. All 14 bits of
CFG[13:0] must be written or they are ignored. Also, if the 16-bit
conversion result is not read back before tDATA elapses, it is lost.
The SDO data is valid on both SCK edges. Although the rising
edge can be used to capture the data, a digital host using the
SCK falling edge allows a faster reading rate, provided it has an
acceptable hold time. After the optional 17^th (or 31^st) SCK
falling edge, SDO returns to high impedance. Note that if the
optional SCK falling edge is not used, the busy feature cannot
be detected, as described in the General Timing with a Busy
Indicator section.
If CFG readback is enabled, the CFG register associated with
the conversion result is read back MSB first following the LSB of
the conversion result. A total of 31 SCK falling edges is required
to return SDO to high impedance if this is enabled.
DIGITAL HOST
MISO
IRQ
SS
MOSI
SCK
t_DATA
FOR SPI USE CPHA = 1, CPOL = 1.
Figure 42. Connection Diagram for the AD7682/AD7689 with a Busy Indicator
t_CYC
t_ACQ
t_CNVH
t_CONV
t_DATA
CNV
CONVERSION
(n – 1)
SCK
DIN
SDO
CONVERSION (n – 1)
t_SCKH
t_SCK
15
t_SCKL
16 ^17/
31
X
X
X
END CFG (n)
LSB
+1
LSB
END DATA (n – 2)
(QUIET
TIME)
ACQUISITION (n)
UPDATE (n)
CFG/SDO
t_DIS
t_EN
1
2
t_SDI^t_NHDIN
CFG CFG
MSB MSB –1
BEIGN CFG (n + 1)
MSB
MSB
–1
tt_HDSSDDOO
BEGIN DATA (n – 1)
NOTES:
1. THE LSB IS FOR CONVERSION RESULTS OR THE CONFIGURATION REGISTER CFG (n – 1) IF
16 SCK FALLING EDGES = LSB OF CONVERSION RESULTS.
30 SCK FALLING EDGES = LSB OF CONFIGURATION REGISTER.
ON THE 17TH OR 31st SCK FALLING EDGE, SDO IS DRIVEN TO HIGH IMPENDANCE.
OTHERWISE, THE LSB REMAINS ACTIVE UNTIL THE BUSY INDICATOR IS DRIVEN LOW.
CONVERSION (n)
SEE NOTE
15
16
17/
31
(QUIET ACQUISITION
TIME)
(n + 1)
UPDATE (n + 1)
CFG/SDO
t_EN
t_DIS
X
X
X
END CFG (n + 1)
t_DIS
LSB
+1
LSB
END DATA (n – 1) ^{SEE NOTE}
t_EN
Figure 43. Serial Interface Timing for the AD7682/AD7689 with a Busy Indicator
Rev. D | Page 30 of 32