ADS944 datasheet(5/8 Pages) ETC

5 / 8 page

ADS-944

TIMING

The ADS-944 is an edge-triggered device. A conversion is

initiated by the rising edge of the start convert pulse and no

additional external timing signals are required. The device

does not employ "pipeline" delays to increase its throughput

rate. It does not require multiple start convert pulses to bring

valid digital data to its output pins.

Approximately 10ns after the rising edge of the start convert

signal, the ADS-944's internal sample-hold amplifier is driven

into the hold mode by the internal S/H control line. After a

35ns delay to allow for S/H output transient settling, the

conversion process begins, and the EOC line (pin 16) is driven

high. The complete A/D conversion requires approximately

150ns. The falling of EOC signals that the conversion is now

complete and digital output data is now valid.

This device actually guarantees that digital output data will be

valid for 10ns prior to the falling edge of EOC. Therefore, EOC

can be used to latch data into external registers that have

appropriate setup times. Any other available timing edges,

including a delayed EOC or the rising edge of the next EOC

pulse, can also be used for this purpose.

The falling edge of the start convert pulse, though irrelevant to

device timing, can cause conversion errors if it occurs at

certain times. Therefore, the recommended start convert

pulse width is between 40 and 80ns or between 130 and

160ns. DATEL performs ADS-944 production testing at the full

5MHz sampling rate using 80ns start convert pulses.

Table 1. Output Coding

OUTPUT CODING

INPUT RANGE

BIPOLAR

MSB

LSB

MSB

LSB

MSB

LSB

±1.25V

SCALE

OFF. BINARY

COMP. OFF. BIN.

TWO'S COMP.

11 1111 1111 1111

00 0000 0000 0000 01 1111 1111 1111

+1.249847

+FS –1 LSB

11 1000 0000 0000

00 1111 1111 1111

01 1000 0000 0000

+0.937500

+3/4 FS

11 0000 0000 0000

00 1111 1111 1111

01 0000 0000 0000

+0.625000

+1/2FS

10 0000 0000 0000 01 1111 1111 1111

00 0000 0000 0000

0.000000

01 0000 0000 0000 10 1111 1111 1111

11 0000 0000 0000

–0.625000

–1/2FS

00 1000 0000 0000 11 0111 1111 1111

10 1000 0000 0000

–0.937500

–3/4FS

00 0000 0000 0001 11 1111 1111 1110

10 0000 0000 0001

–1.249847

–FS +1 LSB

00 0000 0000 0000 11 1111 1111 1111

10 0000 0000 0000

–1.250000

–FS

Figure 3. ADS-944 Timing Diagram

THERMAL REQUIREMENTS

All DATEL sampling A/D converters are fully characterized and

specified over operating temperature (case) ranges of 0 to

+70°C and –55 to +125°C. All room-temperature (TA = +25°C)

production testing is performed without the use of heat sinks or

forced-air cooling. Thermal impedance figures for each device

are listed in their respective specification tables.

These devices do not normally require heat sinks, however,

standard precautionary design and layout procedures should

be used to ensure devices do not overheat. The ground and

power planes beneath the package, as well as all pcb signal

runs to and from the device, should be as heavy as possible to

help conduct heat away from the package.

Electrically-insulating, thermally-conductive "pads" may be

installed underneath the package. Devices should be

soldered to boards rather than "socketed", and of course,

minimal air flow over the surface can greatly help reduce the

package temperature.

In more severe ambient conditions, the package/junction

temperature of a given device can be reduced dramatically

(typically 35%) by using one of DATEL's HS Series heat sinks.

See Ordering Information for the assigned part number. See

page 1-183 of the DATEL Data Acquisition Components

Catalog for more information on the HS Series. Request

DATEL Application Note AN-8, "Heat Sinks for DIP Data

Converters", or contact DATEL directly, for additional

information.

START

CONVERT

OUTPUT

DATA

INTERNAL S/H

N+1

DATA (N-1) VALID

Acquisition Time

10ns typ.

DATA N VALID

Note: Scale is approximately 10ns per division.

EOC

Conversion Time

INVALID

DATA

35ns typ.

Hold

80ns typ.

115ns typ.

150ns typ., 160ns max.

60ns typ., ±10ns

Hold

140ns min., 150ns typ.

START CONVERT pulse width: 40 to 80ns or 130 to 160ns.

50ns typ., 60ns max.

90ns max.

ADS944 Datasheet(PDF) 5 Page - List of Unclassifed Manufacturers

ADS944 Datasheet(HTML) 5 Page - List of Unclassifed Manufacturers

Html Pages

1 2 3 4 5 6 7 8

Datasheet Download

Link URL