AD7864 Analog Devices, AD7864 Datasheet - Page 16

• Manufacturer Part Number: AD7864
• Description: High Speed, Low Power, 4-channel Simultaneous Sampling, 12-Bit ADC
• Manufacturer: Analog Devices

Specifications of AD7864

• Resolution (bits): 12bit
• # Chan: 4
• Sample Rate: 520kSPS
• Interface: Par
• Analog Input Type: SE-Bip,SE-Uni
• Ain Range: Bip 10V,Bip 2.5V,Bip 5.0V,Uni 2.5V,Uni 5.0V
• Adc Architecture: SAR
• Pkg Type: QFP

AD7864
logic high). The pointer is incremented to point to the next
register (next conversion result) when that conversion result is
available. Thus, FRSTDATA in Figure 9 is shown as going low
just prior to the second EOC pulse. Repeated read operations
during a conversion continue to access the data at the current
pointer location until the pointer is incremented at the end of
that conversion. Note that FRSTDATA has an indeterminate
logic state after initial power-up. This means that for the first
conversion sequence after power-up, the FRSTDATA logic
output may already be logic high before the end of the first
conversion (this condition is indicated by the dashed line in
Figure 9
high as a result of the previous read sequence, as is the case after
the fourth read in
resets the pointer to the first data location. Therefore, FRSTDATA
). Also, the FRSTDATA logic output may already be
Figure 9
SL1 TO SL4
FRSTDATA
FRSTDATA
CONVST
CONVST
H/S SEL
BUSY
DATA
BUSY
DATA
EOC
EOC
. The fourth read (rising edge of
RD
CS
RD
CS
t
2
t
2
t
1
t
1
t
CONV
t
3
Figure 10. Timing Diagram, Reading After the Conversion Sequence
100ns
100ns
t
BUSY
Figure 9. Timing Diagram for Reading During Conversion
t
8
V
t
12
IN1
t
t
10
CONV
t
6
t
4
V
RD)
IN1
Rev. D | Page 16 of 28
t
6
t
BUSY
t
t
11
V
5
IN2
V
IN2
t
t
3
3
t
8
t
CONV
t
t
is already high when the next conversion sequence initiates. See
the
Reading After the Conversion Sequence
Figure 10 shows the same conversion sequence as Figure 9. In
this case, however, the results of the four conversions (on V
V
BUSY goes logic low. The FRSTDATA signal goes logic high at
the end of the first conversion just prior to EOC going logic low.
As mentioned previously, FRSTDATA has an indeterminate
state after initial power-up, therefore FRSTDATA may already
be logic high. Unlike the case when reading between each
conversion, the output data register pointer is incremented on
the rising edge of RD because the next conversion result is
available. This means FRSTDATA goes logic low after the first
rising edge on RD.
7
7
IN4
V
IN3
Accessing the Output Data Registers
) are read after all conversions have finished, that is, when
V
t
4
IN3
V
IN4
t
CONV
t
10
QUIET
TIME
V
IN4
V
IN1
t
ACQ
QUIET
TIME
t
10
section.
IN1
to