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AD7813YNZ View Datasheet(PDF) - Analog Devices

Part NameAD7813YNZ ADI
Analog Devices ADI
Description2.7 V to 5.5 V, 400 kSPS 8-/10-Bit Sampling ADC
AD7813YNZ Datasheet PDF : 12 Pages
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AD7813
Typical Performance Characteristics
10
1
0.1
0.01
0 5 10 15 20 25 30 35 40 45 50
THROUGHPUT kSPS
Figure 10. Power vs. Throughput
0
AD7813
10
2048 POINT FFT
SAMPLING 357.142kHz
20
fIN 30.168kHz
30
40
50
60
70
80
90
100
0 17 35 52 70 87 105 122 140 157 174
FREQUENCY kHz
Figure 11. SNR
TIMING AND CONTROL
The AD7813 has only one input for timing and control, i.e.,
the CONVST (convert start signal). The rising edge of this
CONVST signal initiates a 1.5 µs pulse on an internally gener-
ated CONVST signal. This pulse is present to ensure the part
has enough time to power up before a conversion is initiated. If
the external CONVST signal is low, the falling edge of the
internal CONVST signal will cause the sampling circuit to go
into hold mode and initiate a conversion. If, however, the exter-
nal CONVST signal is high when the internal CONVST goes
low, it is upon the falling edge of the external CONVST signal
that the sampling circuitry will go into hold mode and initiate a
conversion. The use of the internally generated 1.5 µs pulse,
as previously described, can be likened to the configuration
shown in Figure 12. The application of a CONVST signal at
the CONVST pin triggers the generation of a 1.5 µs pulse. Both
the external CONVST and this internal CONVST are input to
an OR gate. The resulting signal has the duration of the longer
of the two input signals. Once a conversion has been initiated
the BUSY signal goes high to indicate a conversion is in progress.
At the end of conversion the sampling circuit goes back into its
tracking mode again. The end of conversion is indicated by the
BUSY signal going low. This signal may be used to initiate an
ISR on a microprocessor. At this point the conversion result is
latched into the output register where it may be read. The AD7813
has an 8-bit wide parallel interface. The 10-bit conversion result
is accessed by performing two successive read operations. The
first 8-bit read accesses the 8 MSBs of the conversion result and
the second read accesses the 2 LSBs, as illustrated in Figure 13,
where one performance of the two successive reads is highlighted
after the falling edge of BUSY. The state of the external CONVST
signal at the end of conversion also establishes the mode of opera-
tion of the AD7813.
Mode 1 Operation (High Speed Sampling)
If the external CONVST is logic high when BUSY goes low, the
part is said to be in Mode 1 operation. While operating in Mode
1, the AD7813 will not power down between conversions. The
AD7813 should be operated in Mode 1 for high speed sampling
applications, i.e., throughputs greater than 100 kSPS. Figure 13
shows the timing for Mode 1 operation. From this diagram one
can see that a minimum delay of the sum of the conversion time
and read time must be left between two successive falling edges
of the external CONVST. This is to ensure that a conversion is
not initiated during a read.
Mode 2 Operation (Automatic Power-Down)
At slower throughput rates the AD7813 may be powered down
between conversions to give a superior power performance.
This is Mode 2 Operation and it is achieved by bringing the
CONVST signal logic low before the falling edge of BUSY.
Figure 14, overleaf, shows the timing for Mode 2 Operation.
The falling edge of the external CONVST signal may occur
before or after the falling edge of the internal CONVST signal,
but it is the later occurring falling edge of both that controls
when the first conversion will take place. If the falling edge
of the external CONVST occurs after that of the internal
CONVST, it means that the moment of the first conversion is
controlled exactly, regardless of any jitter associated with the
internal CONVST signal. The parallel interface is still fully
operational while the AD7813 is powered down. The AD7813
is powered up again on the rising edge of the CONVST signal.
The gated CONVST pulse will now remain high long enough
for the AD7813 to fully power up, which takes about 1.5 µs. This
is ensured by the internal CONVST signal, which will remain high
for 1.5 µs.
CONVST
(PIN 4)
EXT
INT
1.5s
Figure 12.
GATED
8
REV. C
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GENERAL DESCRIPTION
The AD7813 is a high-speed, microprocessor-compatible, 8-/10-bit analog-to-digital converter with a maximum throughput of 400 kSPS. The converter operates off a single 2.7 V to 5.5 V supply and contains a 2.3 µs successive approximation A/D converter, track/hold circuitry, on-chip clock oscillator and 8-bit wide parallel interface. The parallel interface is designed to allow easy interfacing to microprocessors and DSPs. The 10-bit conversion result is read by carrying out two 8-bit read opera tions. The first read operation accesses the 8 MSBs of the ADC conversion result and the second read accesses the 2 LSBs. Using only address decoding logic the AD7813 is easily mapped into the microprocessor address space.

FEATURES
   8-/10-Bit ADC with 2.3 μs Conversion Time
   On-Chip Track and Hold
   Operating Supply Range: 2.7 V to 5.5 V
   Specifications at 2.7 V–3.6 V and 5 V  10%
   8-Bit Parallel Interface
      8-Bit + 2-Bit Read
   Power Performance
      Normal Operation
         10.5 mW, VDD = 3 V
      Automatic Power-Down
         34.6 μW @ 1 kSPS, VDD = 3 V
   Analog Input Range: 0 V to VREF
   Reference Input Range: 1.2 V to VDD

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