ADC0804LCWMXSLASHNOPB datasheet(26/56 Pages) TI1

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ADC0801, ADC0802, ADC0803, ADC0804, ADC0805

SNOSBI1C – NOVEMBER 2009 – REVISED JUNE 2015

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*Add if VREF/2

≤ 1 VDC with LM358 to draw 3 mA to ground.

Figure 34. Accommodating an Analog Input from 0.5V (Digital Out = 00HEX) to 3.5 V (Digital Out=FFHEX)

9.2.1.2.4

Errors and Reference Voltage Adjustments

9.2.1.2.4.1

Zero Error

The zero of the ADC does not require adjustment. If the minimum analog input voltage value, VIN(MIN), is not

ground, a zero offset can be done. The converter can be made to output 0000 0000 digital code for this minimum

input voltage by biasing the ADC VIN(−) input at this VIN(MIN) value (see Application Information). This uses the

differential mode operation of the ADC.

The zero error of the ADC converter relates to the location of the first riser of the transfer function and can be

measured by grounding the VIN(−) input and applying a small magnitude positive voltage to the VIN(+) input. Zero

error is the difference between the actual DC input voltage that is necessary to just cause an output digital code

transition from 0000 0000 to 0000 0001 and the ideal 1/2 LSB value (1/2 LSB = 9.8 mV for VREF/2=2.500 VDC).

9.2.1.2.4.2

Full-Scale

The full-scale adjustment can be made by applying a differential input voltage that is 11/2 LSB less than the

desired analog full-scale voltage range and then adjusting the magnitude of the VREF/2 input (pin 9 or the VCC

supply if pin 9 is not used) for a digital output code that is just changing from 1111 1110 to 1111 1111.

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