參數(shù)資料
型號(hào)： EVAL-AD7859CB
廠商： Analog Devices, Inc.
英文描述： 3 V to 5 V Single Supply, 200 kSPS 8-Channel, 12-Bit Sampling ADCs
中文描述： 3 V至5 V單電源，200 kSPS的8通道，12位采樣ADC
文件頁(yè)數(shù)： 14/28頁(yè)
文件大?。?/td> 535K
代理商： EVAL-AD7859CB
AD7859/AD7859L
REV. A
–14–
and 1.5 CLKIN periods are allowed for the acquisition time.
With a 1.8 MHz clock, this gives a full cycle time of 10
μ
s,
which equates to a throughput rate of 100 kSPS.
When using the software conversion start for maximum
throughput, the user must ensure the control register write op-
eration extends beyond the falling edge of BUSY. The falling
edge of BUSY resets the
CONVST
bit to 0 and allows it to be
reprogrammed to 1 to start the next conversion.
TYPICAL CONNECTION DIAGRAM
Figure 8 shows a typical connection diagram for the AD7859/
AD7859L. The AGND and the DGND pins are connected
together at the device for good noise suppression. The first
CONVST
applied after power-up starts a self-calibration
sequence. This is explained in the calibration section of this data
sheet. Note that after power is applied to AV
DD
and DV
DD
and
the
CONVST
signal is applied, the part requires (70 ms + 1/
sample rate) for the internal reference to settle and for the self-
calibration on power-up to be completed.
AV
DD
DV
DD
AIN(+)
AIN(–)
C
REF1
C
REF2
SLEEP
CAL
DB15
DB0
CONVST
AGND
DGND
CLKIN
REF
IN
/REF
OUT
AD7859/
AD7859L
ANALOG
SUPPLY
+3V TO +5V
0.1μF
0.1μF
10μF
0.1μF
0.01μF
CONVERSION
START SIGNAL
0.1nF EXTERNAL REF
0.1μF INTERNAL REF
0V TO 2.5V
INPUT
4MHz/1.8MHz
OSCILLATOR
OPTIONAL
EXTERNAL
REFERENCE
CS
RD
WR
W/B
BUSY
DV
DD
μC/μP
AD780/
REF192
Figure 8. Typical Circuit
For applications where power consumption is a major concern,
the power-down options can be exercised by writing to the part
and using the
SLEEP
pin. See the
Power-Down
section for more
details on low power applications.
CIRCUIT INFORMATION
The AD7859/AD7859L is a fast, 8-channel, 12-bit, single sup-
ply A/D converter. The part requires an external 4 MHz/1.8
MHz master clock (CLKIN), two C
REF
capacitors, a
CONVST
signal to start conversion and power supply decoupling capaci-
tors. The part provides the user with track/hold, on-chip refer-
ence, calibration features, A/D converter and parallel interface
logic functions on a single chip. The A/D converter section of
the AD7859/AD7859L consists of a conventional successive-ap-
proximation converter based around a capacitor DAC. The
AD7859/AD7859L accepts an analog input range of 0 to +V
REF.
V
REF
can be tied to V
DD
. The reference input to the part con-
nected via a 150 k
resistor to the internal 2.5 V reference and
to the on-chip buffer.
A major advantage of the AD7859/AD7859L is that a conver-
sion can be initiated in software, as well as by applying a signal
to the
CONVST
pin. The part is available in a 44-pin PLCC or a
44-pin PQFP package, and this offers the user considerable
spacing saving advantages over alternative solutions. The
AD7859L version typically consumes only 5.5 mW making it
ideal for battery-powered applications.
CONVERTER DETAILS
The master clock for the part is applied to the CLKIN pin.
Conversion is initiated on the AD7859/AD7859L by pulsing the
CONVST
input or by writing to the control register and setting
the CONVST bit to 1. On the rising edge of
CONVST
(or at
the end of the control register write operation), the on-chip
track/hold goes from track to hold mode. The falling edge of the
CLKIN signal which follows the rising edge of
CONVST
ini-
tiates the conversion, provided the rising edge of
CONVST
(or
WR
when converting via the control register) occurs typically at
least 10 ns before this CLKIN edge. The conversion takes 16.5
CLKIN periods from this CLKIN falling edge. If the 10 ns set-
up time is not met, the conversion takes 17.5 CLKIN periods.
The time required by the AD7859/AD7859L to acquire a signal
depends upon the source resistance connected to the AIN(+) in-
put. Please refer to the
acquisition time
section for more details.
When a conversion is completed, the BUSY output goes low,
and the result of the conversion can be read by accessing the
data through the data bus. To obtain optimum performance
from the part, read or write operations should not occur during
the conversion or less than 200 ns prior to the next
CONVST
rising edge. Reading/writing during conversion typically de-
grades the Signal-to-(Noise + Distortion) by less than 0.5 dBs.
The AD7859 can operate at throughput rates of over 200 kSPS
(up to 100 kSPS for the AD7859L).
With the AD7859L, 100 kSPS throughput can be obtained as
follows: the CLKIN and
CONVST
signals are arranged to give
a conversion time of 16.5 CLKIN periods as described above
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