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Topic 5 The Analog Subsystem Slide 12

This portion of the presentation will review the Concerto pin connections, beginning on this slide with the details of ADC-1. Starting at the top, there are six analog only input pins; A0, B0, A3, B3, A7, and B7. As can be seen in the diagram, on the left side are the pin connections and on the right side is the converter. Inputs A0, B0, A3, B3, A7 and B7 are shown going directly into the converter. There is no analog connected to these six pins, no DAC or comparator is connected to them. Therefore these pins are typically the quietest pins, the ones that would be best suited to the most critical signals, the inputs used for the best conversions. The device is designed to allow simultaneous sample-and-hold with three pairs of signals, such as three voltages, maybe three currents, and so forth. In this simultaneous sample-and-hold mode A0 and B0 would be ADC1 channel zero, channel three would be A3 and B3, and A7 and B7 would be channel seven. The four shared pins, A2, A4, B4, and A6 are shared by the AIO and comparators. Each of the four pins has an AIO connected to it, a comparator connection and is also connected to the converter, giving these pins considerable functionality. A possible application would be to choose a MUX connection to keep any analog input from coming in, to use this as a digital output. To do a comparison it is not necessary to use a converter on these devices, the comparators are truly analog comparators, just like on Piccolo. These are very fast, analog comparators capable of tripping the PWMs in 20 to 25 nS. The analog comparators can also be used to compare with the DAC inputs. Three DAC outputs are connected to the ADC inputs. Two of these, B2 and B6, have no pin connection at all. B2 and B6 are each connected to their own DAC, which is connected to a comparator and is also connected to B2 and B6 on ADC1. This could be used to verify that the ADC is truly functional, which is important in a safety application. The DAC could be used to exercise the B2 input over the full voltage rail and to check that the ADC is tracking the voltage from 0 to 3.3 V. There are creative things that can be done as part of a safety plan to make sure that the ADC is functioning correctly. B4 can be connected to a DAC, but it is also connected to a pin and can be used as a standard analog signal input. Comparator 2 is different from Comparator 1 and Comparator 3. It actually has the ability to not only compare an analog signal into a DAC value but it can compare two analog signals, the analog signals on A4 and B4. At reset the four AIO lines are configured as inputs and they are disabled. If it is necessary to use them as outputs, the user will to have to change the MUX for them to an output and for the MUX not to use the analog signal but to use the AIO mode, and then enable it. Another detail to note is that VREFLO is connected to B5. This is important from the standpoint that when the part is shipped from TI, it is shipped as a zero offset device. When it is actually populated on a board, there is going to be a different offset value, and measuring VREFLO with B5 gives the user the capability to measure the offset for their particular board. Also, there is a temperature sensor connected to A5 that can be used for temperature compensation in the system, or calibrating the onboard oscillators over temperature, or calibrating high resolution PWMs.

PTM Published on: 2012-02-23