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ADS-944MM Datasheet(PDF) 5 Page - List of Unclassifed Manufacturers |
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ADS-944MM Datasheet(HTML) 5 Page - List of Unclassifed Manufacturers |
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5 / 8 page  ADS-944 5 ® ® 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 0 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 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. |
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