AD7949 Analog Devices, AD7949 Datasheet - Page 27

• Manufacturer Part Number: AD7949
• Description: 14-Bit, 8-Channel, 250 kSPS PulSAR ADC
• Manufacturer: Analog Devices

Specifications of AD7949

• Resolution (bits): 14bit
• # Chan: 8
• Sample Rate: 250kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Adc Architecture: SAR
• Pkg Type: CSP

Data Sheet
READ/WRITE SPANNING CONVERSION WITH A
BUSY INDICATOR
This mode is used when the AD7949 is connected to any host
using an SPI, serial port, or FPGA with an interrupt input. The
connection diagram is shown in Figure 41, and the correspond-
ing timing is given in Figure 42. 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, t
conversion time, t
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 AD7949 enters the
acquisition phase and power-down. The host must enable the
MSB of the CFG register at this time (if necessary) to begin the
CONVERSION
NOTES:
1. THE LSB IS FOR CONVERSION RESULTS OR THE CONFIGURATION REGISTER CFG (n – 1) IF
CNV
14 SCK FALLING EDGES = LSB OF CONVERSION RESULTS.
28 SCK FALLING EDGES = LSB OF CONFIGURATION REGISTER.
ON THE 15TH OR 29TH SCK FALLING EDGE, SDO IS DRIVEN TO HIGH IMPEDANCE.
OTHERWISE, THE LSB REMAINS ACTIVE UNTIL THE BUSY INDICATOR IS DRIVEN LOW.
SCK
SDO
DIN
(n – 1)
CONV
t
SCKH
END DATA (n – 2)
t
, to generate the busy signal indicator.
SCKL
END CFG (n)
DATA
CONVERSION (n – 1)
t
13
DATA
X
t
SCK
, and then held low beyond the
14
LSB
X
+ 1
15/
29
X
LSB
Figure 42. Serial Interface Timing for the AD7949 with a Busy Indicator
Figure 41. Connection Diagram for the AD7949 with a Busy Indicator
t
DIS
(QUIET
TIME)
t
UPDATE (n)
EN
t
CFG/SDO
CYC
AD7949
BEIGN CFG (n + 1)
FOR SPI USE CPHA = 1, CPOL = 1.
MSB
CFG
MSB
SDO
CNV
SCK
1
DIN
t
SDIN
BEGIN DATA (n – 1)
MSB –1
Rev. C | Page 27 of 32
MSB
CFG
t
– 1
HDIN
ACQUISITION (n)
2
t
ACQ
VIO
t
t
HSDO
DSDO
MISO
IRQ
SS
MOSI
SCK
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 14 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 t
CFG[13:0] must be written or they are ignored. Also, if the 14-bit
conversion result is not read back before t
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 15
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 29 SCK falling edges is required
to return SDO to high impedance if this is enabled.
DIGITAL HOST
DATA
t
t
CNVH
EN
time elapses for the next conversion. All 14 bits of
t
DIS
END DATA (n – 1)
END CFG (n + 1)
t
CONVERSION (n)
13
X
DATA
t
CONV
LSB
14
NOTE 1
X
+ 1
NOTE 1
15/
29
LSB
X
t
DATA
DIS
th
(QUIET
(or 29
TIME)
UPDATE (n + 1)
elapses, it is lost.
t
EN
CFG/SDO
st
ACQUISITION
) SCK
AD7949
(n + 1)