ADS-945
3
®®
+25°C
0 to + 0°C
55 to +125°C
DYNAMIC PERFORMANCE
MIN.
TYP.
MAX.
MIN.
TYP.
MAX.
MIN.
TYP.
MAX.
UNITS
S/H Acquisition Time
( to ±0.003%FSR, 2.5V step)
—
40
—
—
40
—
—
40
—
ns
Overvoltage Recovery Time ➄
—
30
100
—
30
100
—
30
100
ns
A/D Conversion Rate
10
—
—
10
—
—
10
—
—
MHz
ANALOG OUTPUT
Reference Output
+9.95
+10
+10.05
+9.95
+10
+10.05
+9.95
+10
+10.05
Volts
Reference Temperature Drift
—
±40
—
—
±40
—
—
±40
—
ppm/°C
Reference Load Current
—
—
2.0
—
—
2.0
—
—
2.0
mA
DIGITAL OUTPUTS
Logic Levels
Logic "1"
+2.7
—
—
+2.7
—
—
+2.7
—
—
Volts
Logic "0"
—
—
+0.5
—
—
+0.5
—
—
+0.5
Volts
Logic Loading "1"
—
—
–0.4
—
—
–0.4
—
—
–0.4
mA
Logic Loading "0"
—
—
–8
—
—
–8
—
—
–8
mA
Delay, Rising Edge of Start Convert
to Output Data Valid
—
—
35
—
—
35
—
—
35
ns
Delay, Edge of ENABLE
to Output Data Valid/Invalid
—
—
18
—
—
18
—
—
18
ns
Output Coding
Complementary Offset Binary
POWER REQUIREMENTS
Power Supply Ranges
+15V Supply
+14.25
+15.0
+15.75
+14.25
+15.0
+15.75
+14.25
+15.0
+15.75
Volts
–15V Supply
–14.25
–15.0
–15.75
–14.25
–15.0
–15.75
–14.25
–15.0
–15.75
Volts
+5V Supply
+4.75
+5.0
+5.25
+4.75
+5.0
+5.25
+4.75
+5.0
+5.25
Volts
–5.2V Supply
–4.95
–5.2
–5.45
–4.95
–5.2
–5.45
–4.95
–5.2
–5.45
Volts
Power Supply Currents ➅
+15V Supply
—
+35
+45
—
+35
+45
—
+35
+45
mA
–15V Supply
—
–10
–20
—
–10
–20
—
–10
–20
mA
+5V Supply
—
+290
+320
—
+290
+320
—
+290
+320
mA
–5.2V Supply
—
–350
–390
—
–350
–390
—
–350
–390
mA
Power Dissipation
—
4.0
4.3
—
4.0
4.3
—
4.0
4.3
Watts
Power Supply Rejection
—
—
±0.04
—
—
±0.04
—
—
±0.04
%FSR/%V
Footnotes:
➀ 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.
➁ The input to the ADS-945 is internally clamped at ±2.3V.
➂ An 50ns wide start convert pulse is used for all production testing. For
applications requiring less than a 10MHz sampling rate, a wider start convert
can be used.
6.02
(SNR + Distortion) – 1.76 +
20 log
Full Scale Amplitude
Actual Input Amplitude
➃ Effective bits is equal to:
➄ This is the time required before the A/D output is valid after the analog input is
back within its range.
➅ Typical +5V and –5.2V current drain breakdowns are as follows:
+5VAnalog = +195mA
–5.2VAnalog = –170mA
+5VDigital
= + 95mA
–5.2VDigital = –180mA
+5VTotal
= +290mA
–5.2VTotal = –350mA
TECHNICAL NOTES
1. Obtaining fully specified performance from the ADS-945
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 perfor-
mance, tie all ground pins directly to a large analog ground
plane beneath the package.
Bypass all power supplies to ground with 10µF tantalum
capacitors in parallel with 0.1µF ceramic capacitors. The
bypass capacitors should be located as close to the
unit as possible.
2. The ADS-945 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 Figure 2. The typical
adjustment range is ±0.2%FSR for this circuitry.
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. To enable the three-state outputs, apply a logic "0" (low) to
OUTPUT ENABLE (pin 34). To disable, apply a logic "1"
(high) to pin 34.
4. A passive bandpass filter (Allen Avionics F4202 Series) is
used at the input of the A/D for all production testing.
5. The ADS-945's digital outputs should not be directly con-
nected to a noisy data bus. Drive the bus with 573 or 574
type latches and use "low-noise" logic, such as the 74ALS
series.
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