Datasheet

MICROPROCESSOR

DSP

SCLK

SDATA

GND

ADC081S021

LP2950

1 PF

0.1 PF 0.1 PF1 PF

ADC081S021

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SNAS308G –APRIL 2005–REVISED MAY 2016

Product Folder Links: ADC081S021

9.2 Typical Application

The ADC081S021 is a low-power, single-channel CMOS 8-bit analog-to-digital converter that uses the supply

voltage as a reference, enabling the devices to operate with a full-scale input range of 0 to VA. An example low

power application with the LMT87 which is a wide range ±0.3°C (typical) accurate temperature sensor is shown

in Figure 24.

Figure 24. Typical Application Circuit

9.2.1 Design Requirements

A successful ADC081S021 and LMT87 design is contrained by the following factors:

• VIN range needs to be 0 V to VA where VA can range from 2.7 V to 5.25 V

• Output level of the LMT87 can range from 538 mV to 3277 mV (which satisfies the VIN condition)

9.2.2 Detailed Design Procedure

Designing for an accurate measurement requires careful attention to timing requirements for the ADC081S021.

Because the ADC081S021 uses the supply voltage as a reference, it is important to make sure that the supply

voltage is settled to its final level before exiting the shutdown mode and beginning a conversion. After the supply

voltage is settled, the CS is brought to a low level (ideally 0 V) to start a conversion.

It is also important to ensure that any noise on the power supply must be less than ½ LSB in amplitude. The

supply voltage must be regarded as a precise voltage reference.

After the CS is brought low, the user needs to wait for one complete conversion cycle (approximately 1 μs) for

meaningful data. The dummy conversion cycle can be considered the start-up time of the ADC081S021.

The ADC081S021 digital output can then be correlated to the LMT87 output level to get an accurate temperature

reading. At VDD = 2.7 V, 1 LSB of ADC081S021 is 10.54 mV. This information can be used to calculate the

output level of LMT87 which can then be correlated to temperature.