
ADS -947
3
+25°C
TYP.
0 to +70°C
TYP.
–55 to +125°C
TYP.
DYNAMIC PERFORMANCE
(Cont.)
MIN.
MAX.
MIN.
MAX.
MIN.
MAX.
UNITS
S/H Acquisition Time
( to ±0.003%FSR, 4V step)
Overvoltage Recovery Time
A/D Conversion Rate
—
—
10
40
—
—
45
100
—
—
—
10
40
—
—
45
100
—
—
—
10
40
—
—
45
100
—
ns
ns
MHz
DIGITAL OUTPUTS
Logic Levels
Logic "1"
Logic "0"
Logic Loading "1"
Logic Loading "0"
Output Coding
+2.4
—
—
—
—
—
—
—
—
+0.4
–4
+4
+2.4
—
—
—
—
—
—
—
Offset Binary
—
+0.4
–4
+4
+2.4
—
—
—
—
—
—
—
—
+0.4
–4
+4
Volts
Volts
mA
mA
POWER REQUIREMENTS
Power Supply Ranges
+5V Supply
–5.2V Supply
Power Supply Currents
+5V Supply
–5.2V Supply
Power Dissipation
Power Supply Rejection
+4.75
–4.75
+5.0
–5.2
+5.25
–5.45
+4.75
–4.75
+5.0
–5.2
+5.25
–5.45
+4.9
–4.9
+5.0
–5.2
+5.25
–5.45
Volts
Volts
—
—
—
—
+250
–200
2.0
—
+260
–210
2.25
±0.1
—
—
—
—
+250
–200
2.0
—
+260
–210
2.25
±0.1
—
—
—
—
+250
–200
2.0
—
+260
–210
2.25
±0.1
mA
mA
Watts
%FSR/%V
Footnotes:
All power supplies should be on before applying a start convert pulse. All
supplies and the clock (start convert pulses) must be present during warmup
periods. The device must be continuously converting during this time.
TECHNICAL NOTES
1. Obtaining fully specified performance from the ADS-947
requires careful attention to pc card layout and power
supply decoupling. The device’s analog and digital ground
systems are connected to each other internally. For optimal
performance, tie all ground pins (14, 19 and 24) directly to a
large analog ground plane beneath the package.
Bypass all power supplies to ground with 4.7μF tantalum
capacitors in parallel with 0.1μF ceramic capacitors. Locate
the bypass capacitors as close to the unit as possible.
2. The ADS-947 achieves its specified accuracies without the
need for external calibration. If required, the device’s small
initial offset and gain errors can be reduced to zero using
the adjustment circuitry shown in Figures 2 and 3.
When using this circuitry, or any similar offset and gain
calibration hardware, make adjustments following warmup.
To avoid interaction, always adjust offset before gain.
3. Applying a start convert pulse while a conversion is in
progress (EOC = logic 1) will initiate a new and inaccurate
conversion cycle. Data for the interrupted and subsequent
conversions will be invalid.
4. A passive bandpass filter is used at the input of the A/D for
all production testing.
Figure 2. Optional ADS-947 Gain Adjust Calibration Circuit
Contact DATEL for other input voltage ranges.
A 10MHz clock with a 20ns positive pulse width is used for all production
testing. See Timng Diagram figure 4, for more details.
To Pin 21
of ADS-947
–5V
SIGNAL
INPUT
GAIN
ADJUST
1.98k
50
+5V
2k
This is the time required before the A/D output data is valid once the analog
input is back within the specified range. This time is only guaranteed if the
input does not exceed ±2.2V (S/H saturation voltage).
The mnimumsupply voltages of +4.9V and –5.1V for ±V
DD
are required for
–55°C operation only. The mnimumlimts are +4.75V and –4.95V when
operating at +125°C
Effective bits is equal to:
(SNR + Distortion) – 1.76 + 20 log
Full Scale Amplitude
Actual Input Amplitude
6.02