ADC20D1X00

ADC1xD1x00 Pin Compatibility ADC1xD1x00 Pin Compatibility In order to facilitate upgrading applications from a 10-bit Gig ADC to a 12-bit Gig ADC, the ADC10D1x00 (ADC10D1500/ ADC10D1000) is designed to be pin-compatible with the ADC12D1x00 (ADC12D1800/1600/1000). This means that a single board layout may be designed with both resolution ADCs in mind for more cost efficient and time-to-market product development. National Semiconductor Application Note 2128 Marjorie Plisch March 8, 2011 ADC10D1x00 vs. ADC12D1x00 The only difference on the pin-out between the ADC10D1x00 and the ADC12D1x00 is that the ADC12D1x00 has two additional data bits for each output data bank. Bits for the ADC12D1x00 correspond to Bits for the ADC10D1x00. The placeholders for the two additional bits for the ADC12D1x00 are labeled as RSV bits on the ADC10D1x00. The RSV bits on the ADC10D1x00 correspond to the two LSB, Bits, on the ADC12D1x00, see Table 1. TABLE 1. ADC1xD1x00 LSB Pins Ball No. V10/U10 Y10/W10 W19/W20 W18/V17 B19/B20 B18/C17 C10/D10 A10/B10 ADC10D1x00 Name ADC12D1x00 Name RSV7+/RSV6+/RSV5+/RSV4+/RSV3+/RSV2+/RSV1+/RSV0+/DQd1+/DQd0+/DQ1+/DQ0+/DI1+/DI0+/DId1+/DId0+/- 30153301 FIGURE 1. RSV Pin Termination Datasheet vs. Reference Board For a few exceptions, National’s Reference Board does not follow the datasheet recommendations for certain pin connections. These exceptions are listed below in Table 2 . Historically, the exceptions exist because the Reference Board was developed before silicon development was finalized. In every case, it is correct to follow the datasheet recommendation. ‘DNC’ stands for ‘Do Not Connect’ and ‘NC’ stands for ‘Not Connected.’ TABLE 2. Datasheet vs. RB Comparison Ball No. C6 C7 E3/F4 D1 D7 U7 W3 ADC1xD1x00 National Reference Board Datasheet Name Connection VA NC DNC/DNC DNC DNC DNC DNC POREN (from FPGA) WSS (from FPGA) VTEST+/- (to header) GND VNEGI (shorted to J4/K2) VNEGQ (shorted to L2/M4) CALFAIL (to FPGA) Terminating RSV pins on the ADC10D1x00 The RSV pins may be terminated in a way which makes one board usable for both ADC10D1x00 and ADC12D1x00, see Figure 1. On the ADC10D1x00, the RSV pins are high impedance, so only the 100Ω differential termination resistor for the LVDS driver from the ADC is necessary to be compatible with the ADC12D1x00. However, if these pins are terminated into an FPGA and it is necessary for them to be forced to a known voltage, then the additional 1kΩ resistors can be added to the design; the specific value of the 1kΩ resistors may be changed based upon the requirements of the specific FPGA. For a board which is populated with an ADC12D1x00, the 1kΩ resistors should be left unpopulated. AN-2128 © 2011 National Semiconductor Corporation 301533 www.national.com AN-2128 The following is an explanation of the differences: • C6 – This pin was used for an internal test function for preproduction silicon, but it is not bonded in production parts. • C7 – This pin was used for an internal test function; it is not bonded in production parts and may be connected to any potential or left floating. • E3/F4 – These pins are used for internal test functions; do not connect them. • D1 – This pin was used for an internal test function for preproduction silicon, but it is internally bonded in production parts. • D7 – On an earlier version of the silicon, J4/K2/D7 were shorted externally. On final silicon, D7 is connected to the other pins internally, so it is no longer necessary to do so externally. • U7 – On an earlier version of the silicon, L2/M4/U7 were shorted externally. On final silicon, U7 is connected to the other pins internally, so it is no longer necessary to do so externally. • W3 – This pin is used for an internal test function; do not connect it. Despite its name, note that the CALFAIL pin does not indicate that the execution of the calibration process has actually failed. Planning for Power Consumption In general, higher speed ADCs consume more power and the ADC12D1x00 family consumes more power than the ADC10D1x00. If a system will be upgraded from a 10-bit to 12-bit ADC, take care to design the power supply accordingly with margin, so that it can supply the maximum required power. 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