AD7880CRZ-REEL Analog Devices Inc, AD7880CRZ-REEL Datasheet - Page 5

• Manufacturer Part Number: AD7880CRZ-REEL
• Description: IC ADC 12BIT MONO LP 24-SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD7880CRZ-REEL

• Number Of Bits: 12
• Sampling Rate (per Second): 66k
• Data Interface: Parallel
• Number Of Converters: 1
• Power Dissipation (max): 50mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (0.300", 7.50mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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CIRCUIT INFORMATION
The AD7880 is a +5 V single supply 12-bit A/D converter. The
part requires no external components apart from a 2.5 MHz ex-
ternal clock and power supply decoupling capacitors. It contains
a 12-bit successive approximation ADC based on a fast-settling
voltage-output DAC, a high speed comparator and SAR, as well
as the necessary control logic. The charge balancing comparator
used in the AD7880 provides the user with an inherent track-
and-hold function. The ADC is specified to work with sampling
rates up to 66 kHz.
CONVERTER DETAILS
The AD7880 conversion cycle is initiated on the rising edge of
the CONVST pulse, as shown in the timing diagram of Figure
1. The rising edge of the CONVST pulse places the track/hold
amplifier into “HOLD” mode. The conversion cycle then takes
between 26 and 28 clock periods. The maximum specified con-
version time is 12 s. This corresponds to a conversion cycle
time of 28 clock periods with a CLKIN frequency of 2.5 MHz
and also includes internal propagation delays. During conver-
sion the BUSY output will remain low, and the output databus
drivers will be three-stated. When a conversion is completed,
the BUSY output will go to a high level, and the result of the
conversion can be read by bringing CS and RD low.
The track/hold amplifier acquires a 12-bit input signal in 3 s.
The overall throughput time for the AD7880 is equal to the
conversion time plus the track/hold acquisition time. For a
2.5 MHz input clock the throughput time is 15 s.
REFERENCE INPUT
For specified performance, it is recommended that the reference
input be tied to V
erence down to 2.5 V though with reduced performance specifi-
cations. Figure 3 shows a graph of signal-to-noise ratio (SNR)
versus V
V
100 mV.
ANALOG INPUT
The AD7880 has two analog input pins, V
4 shows the input circuitry to the ADC sampling comparator.
The on-board attenuator network, made up of equal resistors,
allows for various input ranges.
REF
must not be allowed to go above V
74
72
68
66
64
60
70
62
REF
2
.
F = 51.2kHz
F = 2.525kHz
T = 25 C
IN
A
S
DD
Figure 3. SNR vs. V
. The part, however, will operate with a ref-
3
V
REF
– Volts
DD
REF
4
INA
by more than
and V
INB
. Figure
5
–5–
The AD7880 accommodates three separate input ranges, 0 to
V
sponding to these ranges are shown in Figures 5, 6 and 7.
With V
ranges are 0 V to 5 V, 0 V to 10 V and +5 V, as shown in
Table II.
Analog Input
Range
0 V to +5 V
0 V to +10 V
5 V
REF
V
V
IN
IN
, 0 to 2 V
Figure 6. 0 to 2 V
Figure 5. 0 to V
= 0 TO V
= 0 TO 2V
V
V
REF
INA
INB
V
Figure 7.
IN
V
REF
= V
= V
V
V
±
REF
REF
REF
REF
REF
REF
DD
Figure 4. AD7880 Input Circuit
Table II. Analog Input Ranges
V
V
V
V
and V
and using a nominal V
DD
DD
DD
REF
V
V
AGND
V
AGND
V
V
V
V
INA
V
AGND
INA
INB
INB
REF
REF
REF
V
V
REF
INA
R
INB
R
REF
REF
REF
Bipolar Input Configuration
R
R
Input Connections
V
V
V
V
R
R
Unipolar Input Configuration
R
Unipolar Input Configuration
R
IN
IN
IN
INA
. The input configurations corre-
V
12-BIT DAC
0 TO V
DAC
V
V
AGND
V
12-BIT DAC
0 TO V
12-BIT DAC
0 TO V
DD
INB
IN
REF
REF
of +5 V, the input
SAMPLING
COMPARATOR
+
–
REF
REF
+
–
SAMPLING
COMPARATOR
SAMPLING
COMPARATOR
AD7880
+
–
+
–
Connection
Diagram
Figure 5
Figure 6
Figure 7