The horizontal scale is analog input voltage and the particular points labeled are in steps of 1 LSB As shown, the risers are ideal and have no width. Each tread the range of analog input voltage which provides the same digital output code is therefore 1 LSB wide. Next to each transfer function is shown the corresponding error plot. The 2 error plots always have a constant negative slope and the abrupt upside steps are always 1 LSB in magnitude, unless the device has missing codes.
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The horizontal scale is analog input voltage and the particular points labeled are in steps of 1 LSB As shown, the risers are ideal and have no width.
Each tread the range of analog input voltage which provides the same digital output code is therefore 1 LSB wide. Next to each transfer function is shown the corresponding error plot. The 2 error plots always have a constant negative slope and the abrupt upside steps are always 1 LSB in magnitude, unless the device has missing codes.
To ensure startup under all possible conditions, an external WR pulse is required during the first power-up cycle. A conversion-inprocess can be interrupted by issuing a second start command. Internal clock signals then transfer this 1 to the Q output of DFF1. This allows for asynchronous or wide CS and WR signals. After the 1 is clocked through the 8-bit shift register which completes the SAR operation it appears as the input to DFF2.
As soon as this 1 is output from the shift register, the AND gate, G2, causes the new digital word to transfer to the Three-State output latches. An inverting buffer then supplies the INTR output signal. The normal operation proceeds as follows. Conversion will start from 1 to 8 clock periods after at least one of these inputs makes a lowto-high transition. After the requisite number of clock pulses to complete the conversion, the INTR pin will make a high-to-low transition.
This can be used to interrupt a processor, or otherwise signal the availability of a new conversion. The Output Enable function is achieved by an active low pulse at the RD input pin 2.
Analog Operation The analog comparisons are performed by a capacitive charge summing circuit. Three capacitors with precise ratioed values share a common node with the input to an autozeroed comparator. The net charge corresponds to the weighted difference between the input and the current total value set by the ADC, ADC successive approximation register.
If input bypass capacitors are necessary for noise filtering and high source resistance is desirable to minimize capacitor size, the effects of the voltage drop across this input resistance, due to the average value of the input current, can be compensated by a full scale adjustment while the given source resistor and input bypass capacitor are both in place.
This is possible because the average value of the input current is a precise linear function of the differential input voltage at a constant conversion rate. The VlN - input pin 7 can be used to automatically subtract a fixed voltage value from the input reading tare correction. This is also useful in 4mA - 20mA current loop conversion. In addition, common-mode noise can be reduced by use of the differential input. The maximum error voltage due to this slight time difference between the input voltage samples is given by: 4.
If a lowpass filter is required in the system, use a low-value series resistor 1k for a passive RC section or add an op amp RC active low-pass filter. For low-source-resistance applications 1k , a 0. A series resistor can be used to isolate this capacitor both the R and C are placed outside the feedback loop from the output of an op amp, if used.
Both EMI and undesired digital-clock coupling to these inputs can cause system errors. The source resistance for these inputs should, in general, be kept below 5k. Larger values of source resistance can cause undesired signal pickup.
This scale error depends on both a large source resistance and the use of an input bypass capacitor. An analog input voltage with a reduced span and a relatively large zero offset can be easily handled by making use of the differential input see Reference Voltage Span Adjust. Analog Input Current The internal switching action causes displacement currents to flow at the analog inputs. These current transients occur at the leading edge of the internal clocks. They rapidly decay and do not inherently cause errors as the on-chip comparator is strobed at the end of the clock perIod.
This has been achieved in the design of the IC as shown in Figure Alternatively, a voltage less than 2. Input Bypass Capacitors Bypass capacitors at the inputs will average these charges and cause a DC current to flow through the output resistances of the analog signal sources. If the analog input voltage were to range from 0.
With 0. The full 8 bits of resolution are therefore applied over this reduced analog input voltage range. The requisite connections are shown in Figure For expanded scale inputs, the circuits of Figures 14 and 15 can be used.
The differential analog voltage input has good commonmode-rejection and permits offsetting the analog zero-inputvoltage value. In addition, the voltage reference input can be adjusted to allow encoding any smaller analog voltage span to the full 8 bits of resolution. Conversion Time. Easy Interface to Most Microprocessors?
Dotaxe Adclcn datasheet step size can be adjusted by setting the reference voltage at pin9. That is for every increase of Adclcn datasheet obtained value is 1. Activates ADC; Adclcn datasheet low. It is a pin Single channel 8-bit ADC module. Analog inverting Afclcn normally ground. ADC needs a clock to operate. Clock Input pin; to give external clock.
ADC0804LCN/NOPB National Semiconductor, ADC0804LCN/NOPB Datasheet