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DAC1231LCJ-1 Datasheet(PDF) 10 Page - National Semiconductor (TI) |
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DAC1231LCJ-1 Datasheet(HTML) 10 Page - National Semiconductor (TI) |
10 / 18 page Application Hints (Continued) width If this does not provide a sufficient data hold time at the end of the write cycle a negative edge triggered one- shot can be included between the system write strobe and the WR pin of the DAC This is illustrated in Figure 6 for an exemplary system which provides a 250 ns WR strobe time with a data hold time of only 10 ns The proper data set-up time prior to the latching edge (low to high transition) of the WR strobe is insured if the WR pulse width is within spec and the data is valid on the bus for the duration of the DAC WR strobe 19 Digital Signal Feedthrough A typical microprocessor is a tremendous potential source of high frequency noise which can be coupled to sensitive analog circuitry The fast edges of the data and address bus signals generate frequency components of 10’s of mega- hertz and may cause fast transients to appear at the DAC output even when data is latched internally In low frequency or DC applications low pass filtering can reduce the magnitude of any fast transients This is most easily accomplished by over-compensating the DAC output amplifier by increasing the value of its feedback capacitor In applications requiring a fast output response from the DAC and op amp filtering may not be feasible In this event digital signals can be completely isolated from the DAC circuitry by the use of a DM74LS374 latch until a valid CS signal is applied to update the DAC This is shown in Figure 7 A single TRI-STATE data buffer such as the DM81LS95 can be used to isolate any number of DACs in a system Figure 8 shows this isolating circuitry and decoding hard- ware for a multiple DAC analog output card Pull-up resis- tors are used on the buffer outputs to limit the impedance at the DAC digital inputs when the card is not selected A unique feature of this card is that the DAC XFER strobes are controlled by the data bus This allows a very flexible update of any combination of analog outputs via a transfer word which would contain a zero in the bit position assigned to any of the DACs required to change to a new output value TLH5690-13 FIGURE 7 Isolating Data Bus from DAC Circuitry to Eliminate Digital Noise Coupling 10 |
Similar Part No. - DAC1231LCJ-1 |
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Similar Description - DAC1231LCJ-1 |
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