HD64F36022 datasheet(254/384 Pages) RENESAS

254 / 384 page

Section 14 A/D Converter

Rev. 4.00 Sep. 23, 2005 Page 228 of 354

REJ09B0025-0400

14.6

Usage Notes

14.6.1

Permissible Signal Source Impedance

This LSI's analog input is designed such that conversion accuracy is guaranteed for an input signal

for which the signal source impedance is 5 k

Ω or less. This specification is provided to enable the

A/D converter's sample-and-hold circuit input capacitance to be charged within the sampling time;

if the sensor output impedance exceeds 5 k

Ω, charging may be insufficient and it may not be

possible to guarantee A/D conversion accuracy. However, for A/D conversion in single mode with

a large capacitance provided externally, the input load will essentially comprise only the internal

input resistance of 10 k

Ω, and the signal source impedance is ignored. However, as a low-pass

filter effect is obtained in this case, it may not be possible to follow an analog signal with a large

differential coefficient (e.g., 5 mV/

µs or greater) (see figure 14.6). When converting a high-speed

analog signal or converting in scan mode, a low-impedance buffer should be inserted.

14.6.2

Influences on Absolute Accuracy

Adding capacitance results in coupling with GND, and therefore noise in GND may adversely

affect absolute accuracy. Be sure to make the connection to an electrically stable GND.

Care is also required to ensure that filter circuits do not interfere with digital signals or act as

antennas on the mounting board.

20 pF

10 k

Ω

Cin =

15 pF

Sensor output

impedance

to 5 k

Ω

This LSI

Low-pass

filter

C to 0.1

µF

Sensor input

A/D converter

equivalent circuit

Figure 14.6 Analog Input Circuit Example

HD64F36022 Datasheet(PDF) 254 Page - Renesas Technology Corp

HD64F36022 Datasheet(HTML) 254 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL