Intel 8253 - Functional Description

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Typical Applications (Continued)

Functional Description

1.0 UNDERSTANDING A/D ERROR SPECS

A perfect A/D transfer characteristic (staircase waveform) is

shown in

Figure 1

. The horizontal scale is analog input volt-

age and the particular points labeled are in steps of 1 LSB

(19.53 mV with 2.5V tied to the V

REF

/2 pin). The digital out-

put codes that correspond to these inputs are shown as D−1,

D, and D+1. For the perfect A/D, not only will center-value

(A−1, A, A+1, ....)analog inputs produce the correct out-

put digital codes, but also each riser (the transitions between

adjacent output codes) will be located

⁄

LSB away from

each center-value. As shown, the risers are ideal and have

no width. Correct digital output codes will be provided for a

range of analog input voltages that extend

⁄

LSB from the

ideal center-values. Each tread (the range of analog input

voltage that provides the same digital output code) is there-

fore 1 LSB wide.

Sampling an AC Input Signal

DS005671-78

Note 11: Oversample whenever possible [keep fs

2f(−60)] to eliminate input frequency folding (aliasing) and to allow for the skirt response of the filter.

Note 12: Consider the amplitude errors which are introduced within the passband of the filter.

Power Savings by Clock Gating

DS005671-79

(Complete shutdown takes ≈ 30 seconds.)

Power Savings by A/D and V

REF

Shutdown

DS005671-80

*Use ADC0801, 02, 03 or 05 for lowest power consumption.

Note: Logic inputs can be driven to V

with A/D supply at zero volts.

Buffer prevents data bus from overdriving output of A/D when in shutdown mode.

ADC0801/ADC0802/ADC0803/ADC0804/ADC0805