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ADC0844 Просмотр технического описания (PDF) - National ->Texas Instruments

Номер в каталогеADC0844 National-Semiconductor
National ->Texas Instruments National-Semiconductor
Компоненты Описание8-Bit μP Compatible A/D Converters with Multiplexer Options
ADC0844 Datasheet PDF : 24 Pages
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grounding the Vinput and applying a small magnitude pos-
itive voltage to the V+ input. Zero error is the difference
between actual DC input voltage which is necessary to just
cause an output digital code transition from 0000 0000 to
0000 0001 and the ideal ½ LSB value (½ LSB=9.8 mV for
VREF=5.000 VDC).
4.2 Full-Scale
The full-scale adjustment can be made by applying a differ-
ential input voltage which is 1 ½ LSB down from the desired
analog full-scale voltage range and then adjusting the mag-
nitude of the VREF input for a digital output code changing from
1111 1110 to 1111 1111.
4.3 Adjusting for an Arbitrary Analog Input Voltage
Range
If the analog zero voltage of the A/D is shifted away from
ground (for example, to accommodate an analog input signal
which does not go to ground), this new zero reference should
be properly adjusted first. A VIN (+) voltage which equals this
desired zero reference plus ½ LSB (where the LSB is calcu-
lated for the desired analog span, 1 LSB = analog span/256)
is applied to selected “+” input and the zero reference voltage
at the corresponding “−” input should then be adjusted to just
obtain the 00HEX to 01HEX code transition.
a) Ratiometric
501616
b) Absolute with a Reduced Span
FIGURE 2. Referencing Examples
501617
The full-scale adjustment should be made [with the proper
VIN (−) voltage applied] by forcing a voltage to the VIN (+) input
which is given by:
where VMAX=the high end of the analog input range and
VMIN=the low end (the offset zero) of the analog range. (Both
are ground referenced.)
The VREF (or VCC) voltage is then adjusted to provide a code
change from FEHEX to FFHEX. This completes the adjustment
procedure.
13
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