ad7886kp Analog Devices, Inc., ad7886kp Datasheet - Page 6

• Manufacturer Part Number: ad7886kp
• Description: Lc2mos 12-bit, 750 Khz/1 Mhz, Sampling Adc
• Manufacturer: Analog Devices, Inc.

AD7886
this amplifier typically by 20 MHz which is much greater than
the Nyquist limit of the ADC; as a result, it can be used for
undersampling applications. The track-and-hold amplifier ac-
quires the input signal to 12-bit accuracy in less than 333 ns.
The overall throughput time is equal to the conversion time
plus the track/ hold amplifier acquisition time, which is 1.333 s
for the AD7886.
The operation of the track/hold amplifier is essentially transpar-
ent to the user. The track-to-hold transition occurs at the start
of conversion on the falling edge of CONVST. The conversion
procedure does not start until the rising edge of CONVST. The
width of the CONVST pulse low time determines the track-to
hold settling time. The track/hold reverts back to the track
mode at the end of conversion when BUSY has returned high.
ANALOG INPUT RANGES
The AD7886 has three user selectable analog input ranges: 0 V
to 5 V, 0 V to 10 V and 5 V. Figure 3 shows how to configure
the two analog inputs (VIN1 and VIN2) for these ranges.
UNIPOLAR OPERATION
Figure 4 shows a typical unipolar circuit for the AD7886. The
ideal input/output characteristic is shown in Figure 5. The
designed code transitions occur on integer multiples of 1 LSB.
The output code is natural binary with 1 LSB = FS/4096. FS is
either +5 V or +10 V, depending on how the analog inputs are
configured.
Figure 3. Analog Input Range Configurations
0 TO 10V
0 TO 5V
+5V
5V
VIN1
VIN2
VIN1
VIN2
VIN1
VIN2
0 TO 10V ANALOG INPUT RANGE
0 TO 5V ANALOG INPUT RANGE
10k
10k
10k
10k
10k
10k
5V ANALOG INPUT RANGE
–
+
–
+
–
+
3.5k
3.5k
3.5k
COMPARATORS
COMPARATORS
COMPARATORS
TO
TO
TO
–6–
Figure 5. Ideal Input/Output Transfer Characteristic for
Unipolar Operation
11...110
11...100
00...010
00...000
11...111
11...101
00...011
00...001
OUTPUT
CODE
AD586
GND
Figure 4. Unipolar Operation
+V
+V
**0 TO 5V RANGE: CONNECT VIN2 TO VIN1
*ADDITIONAL PINS OMITTED FOR CLARITY
VIN, INPUT VOLTAGE (LSBS)
IN
0 TO 10V RANGE: CONNECT VIN2 TO AGND
V
OUT
1
10 F
C1
+
5V
2
AD707
0 TO 10V
0 TO 5V
–
+
AIN
OR
0.1 F
3
C2
–
3.5V
1LSB =
VIN1
VIN2**
AGND
+
SUM
V
REF
5REF
AD7886*
–
V
SS
5V
FS – 1LSB
+
V
4096
5V
DD
FS
FS
REV. B