ADS7862YB Burr-Brown Corporation, ADS7862YB Datasheet - Page 10

• Manufacturer Part Number: ADS7862YB
• Description: Dual 500kHz/ 12-Bit/ 2 2 Channel Simultaneous Sampling ANALOG-TO-DIGITAL CONVERTER
• Manufacturer: Burr-Brown Corporation

FIGURE 8. Conversion Mode.
TRANSITION NOISE
Figure 5 shows a histogram plot for the ADS7862 following
8,000 conversions of a DC input. The DC input was set at
output code 2046. All but one of the conversions had an
output code result of 2046 (one of the conversions resulted
in an output of 2047). The histogram reveals the excellent
noise performance of the ADS7862.
FIGURE 5. Histogram of 8,000 Conversions of a DC Input.
BIPOLAR INPUTS
The differential inputs of the ADS7862 were designed to
accept bipolar inputs (–V
reference voltage (2.5V), which corresponds to a 0V to 5V
input range with a 2.5V reference. By using a simple op amp
circuit featuring a single amplifier and four external resis-
tors, the ADS7862 can be configured to except bipolar
inputs. The conventional
ranges can be interfaced to the ADS7862 using the resistor
values shown in Figure 7.
TIMING AND CONTROL
The ADS7862 uses an external clock (CLOCK, pin 19)
which controls the conversion rate of the CDAC. With an
8MHz external clock, the A/D sampling rate is 500kHz
which corresponds to a 2 s maximum throughput time.
8000
7000
6000
5000
4000
3000
2000
1000
0
®
2044
ADS7862
CONVERSION
MODE
NOTE: The ADS7862 will switch from the sample to the hold mode the instant CONVST goes LOW regardless of
the state of the external clock. The conversion process is initiated with the first rising edge of the external clock
following CONVST going LOW.
CONVST
CLOCK
2045
REF
Code (decimal)
and +V
2.5V,
SAMPLE
2046
REF
5V, and
) around the internal
2047
t
3
t
CKH
10V input
HOLD
2048
t
CKP
t
CKL
10
FIGURE 7. Level Shift Circuit for Bipolar Input Ranges.
FIGURE 6. Test Circuits for Timing Specifications.
Three timing diagrams are used to explain the operation of
the ADS7862. Figure 8 shows the timing relationship be-
tween the CLOCK, CONVST (pin 18) and the conversion
Bipolar Input
BIPOLAR INPUT
DATA
Voltage Waveforms for DATA Rise and Fall Times t
t
R
2.5V
10V
5V
DATA
20k
4k
CONVERT
1k
2k
4k
R
1
R
2
OPA132
1.4V
R
10k
20k
1
5k
R
3k
100pF
C
2
LOAD
Test Point
+IN
–IN
REF
2.5V
t
F
ADS7862
OUT
R
, and t
(pin 2)
V
V
OH
OL
F
.