AD7819 Analog Devices, AD7819 Datasheet - Page 8

• Manufacturer Part Number: AD7819
• Description: +2.7 V to +5.5 V, 200 kSPS 8-Bit Sampling ADC
• Manufacturer: Analog Devices

Specifications of AD7819

• Resolution (bits): 8bit
• # Chan: 1
• Sample Rate: 200kSPS
• Interface: Par
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: DIP,SOIC,SOP

AD7819
Typical Performance Characteristics
TIMING AND CONTROL
The AD7819 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 in-
ternal CONVST signal will cause the sampling circuit to go into
hold mode and initiate a conversion. If, however, the external
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
–100
0.01
–10
–20
–30
–40
–50
–60
–70
–80
–90
0.1
10
1
0
0
0
5
7
10
13
15
20
THROUGHPUT – kSPS
FREQUENCY – kHz
20
27
33
25
AD7819
2048 POINT FFT
SAMPLING 136.054kHz
F
40
30
IN
= 29.961kHz
47
35
53
40
45
60
50
66
external CONVST and this internal CONVST are input to an
OR gate. The resultant 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 returns to its track-
ing mode. 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 AD7819 has
an 8-bit wide parallel interface. The state of the external CONVST
signal at the end of conversion also establishes the mode of
operation of the AD7819.
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 AD7819 will not power down between conversions. The
AD7819 should be operated in Mode 1 for high speed sam-
pling 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 succes-
sive 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 AD7819 may be powered down
between conversion 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. Fig-
ure 14 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 conver-
sion 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 AD7819 is
powered down. The AD7819 is powered up again on the rising
edge of the CONVST signal. The gated CONVST pulse will
now remain high long enough for the AD7819 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)
1.5 s
EXT
INT
GATED