ADC0820CNED Philips Semiconductors, ADC0820CNED Datasheet - Page 13

• Manufacturer Part Number: ADC0820CNED
• Description: 8-Bit/ high-speed/ mP-compatible A/D converter with track/hold function
• Manufacturer: Philips Semiconductors

Philips Semiconductors Linear Products
therefore not necessary to filter out these transients by putting an
external cap on the V
within 600ns is used to drive the input. The NE530 is a suitable op
amp for driving the input of the ADC0820.
Inherent Sample-Hold
Another benefit of the ADC0820’s input mechanism is its ability to
measure a variety of high-speed signals without the help of an
external sample-and-hold. In a conventional SAR type converter,
regardless of its speed, the input must remain at least 1/2LSB
stable throughout the conversion process if full accuracy is to be
maintained. Consequently, for many high-speed signals, this signal
must be externally sampled, and held stationary during the
conversion.
Sampled data comparators, by nature of their input switching,
already accomplish this function to a large degree (Section 1.2).
Although the conversion time for the ADC0820 is 1.5 s, the time
through which V
the MS flash ADC uses V
uses V
WR is Low. Even though the two flashes are not done
simultaneously, the analog signal is measured at one instant. The
value of V
due to internal logic propagation delay) will be the measured value.
August 31, 1994
8-Bit, high-speed, P-compatible A/D converter with
track/hold function
IN
as its “zero” input, the ADC0820 only “samples” V
IN
approximately 100ns after the rising edge of WR (100ns
IN
must be 1/2LSB stable is much smaller. Since
IN
terminal, if an input amplifier that can settle
IN
as its “compare” input and the LS ADC
V
IN
(+4V
CC
, 3kHz MAX)
+5V
+5V
40k
27k
Figure 12. Telecom A/D Converter
0.1 F
IN
when
12k
–
+
25k
580
47 F
Input signals with slew rates typically below 100mV/ s can be
converted without error. However, because of the input time
constants, and charge injection through the opened comparator
input switches, faster signals may cause errors. Still, the ADC0820’s
loss in accuracy for a given increase in signal slope is far less than
what would be witnessed in a conventional successive
approximation device. An SAR type converter with a conversion
time as fast as 1 s would still not be able to measure a 5V, 1kHz
sine wave without the aid of an external sample-and-hold. The
ADC0820, with no such help, can typically measure 5V, 7kHz
waveforms.
+5V
+5V
V
V
V
V
GND
Figure 11. 8-Bit Resolution Configuration
IN
REF
DD
REF
(+)
(–)
0.1 F
MODE
47 F
DB7
DB0
WR
INT
CS
RD
V
V
REF
IN
V
V
V
MODE
V
GND
DD
REF
IN
REF
V
DD
(+)
(–)
RDY
INT
CS
RD
Product specification
ADC0820
DB7
DB0