ADS-944

3

®

®

+25°C

0 to +70°C

–55 to +125°C

DYNAMIC PERFORMANCE cont.

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

UNITS

S/H Acquisition Time

( to ±0.003%FSR, 2.5V step)

—

85

90

—

85

90

—

85

90

ns

Overvoltage Recovery Time 

—

200

—

—

200

—

—

200

—

ns

A/D Conversion Rate

5

—

—

5

—

—

5

—

—

MHz

DIGITAL OUTPUTS

Logic Levels

Logic "1"

+2.4

—

—

+2.4

—

—

+2.4

—

—

Volts

Logic "0"

—

—

+0.4

—

—

+0.4

—

—

+0.4

Volts

Logic Loading "1"

—

—

–4

—

—

–4

—

—

–4

mA

Logic Loading "0"

—

—

+4

—

—

+4

—

—

+4

mA

Delay, Edge of ENABLE

to Output Data Valid/Invalid

—

—

10

—

—

10

—

—

10

ns

Output Coding

Offset Binary, Complementary Offset Binary, Two's Complement

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

+4.9

+5.0

+5.25

Volts

–5V Supply

–4.95

–5.2

–5.45

–4.95

–5.2

–5.45

–5.1

–5.2

–5.45

Volts

Power Supply Currents ’

+15V Supply

—

+36

+45

—

+36

+45

—

+36

+45

mA

–15V Supply

—

–55

–65

—

–55

–65

—

–55

–65

mA

+5V Supply

—

+155

+168

—

+155

+168

—

+155

+168

mA

–5.2V Supply

—

–167

–175

—

–167

–175

—

–167

–175

mA

Power Dissipation

—

2.95

3.3

—

2.95

3.3

—

2.95

3.3

Watts

Power Supply Rejection

—

—

±0.05

—

—

±0.05

—

—

±0.05

%FSR/%V

TECHNICAL NOTES

1. Obtaining fully specified performance from the ADS-944

requires careful attention to pc-card layout and power

supply decoupling. The device's analog and digital ground

systems are not connected to each other internally. For

optimal performance, tie all ground pins (4, 6, 11, and 15)

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 capaci-

tors. It is very important that the bypass capacitors be

located as close to the unit as possible. Inductors or

ferrite beads can also be used to improve the power supply

filtering. Refer to Figure 4, the ADS-944 Evaluation Board

Schematic, for more details.

2. The ADS-944 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. 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. Pin 8 (COMP. BITS) selects the ADS-944's digital output

coding. When a logic "1" is applied to pin 8, the output

coding is complementary offset binary. When pin 8 has a

logic "0" applied, the output coding becomes offset binary.

The MSB output (pin 31) may be used under these condi-

tions to achieve two's complement coding. Pin 8 is TTL-

compatible and can be driven with digital logic for those who

want dynamic control of its function. There is an internal

pull-up resistor on this pin, allowing pin 8 to be either

connected to +5V or left open when a logic "1" is needed.

4. To enable the three-state outputs, apply a logic "0" (low) to

OUTPUT ENABLE (pin 9). To disable, apply a logic "1"

(high) to pin 9.

Footnotes:

ΠAll 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.

 When COMP. BITS (pin 8) is low, logic loading "0" will be –350µA for this pin.

Ž An 80ns wide start convert pulse is used for all production testing. The start

convert pulse should be between 40 – 80ns or 130 – 160ns to ensure proper

operations. The latter range could be used for those applications requiring less

than a 5MHz sampling rate.

6.02

(SNR + Distortion) – 1.76 +

20 log

Full Scale Amplitude

Actual Input Amplitude

 Effective bits is equal to:

 This is the time required before the A/D output is valid after the analog input is

back within its range.

–55°C operations only. The minimum limits are +4.75V and –4.95V when

operating at +125°C.

’ Typical +5V and –5.2V current drain breakdowns are as follows: