TC815 datasheet(11/26 Pages) MICROCHIP

11 / 26 page

DS21474B-page 11

TC815

4.0

CONVERSION TIMING

The TC815 analog-to-digital converter uses the con-

ventional dual slope integrating conversion technique

with an added phase that automatically eliminates zero

offset errors. The TC815 gives a zero reading with a

zero volt input.

The TC815 is designed to operate with a 32.768kHz

crystal. The 32kHz crystal is low cost and readily avail-

able; it serves as a time-base oscillator crystal in many

digital clocks. (See External Crystal Sources.)

The external clock is divided by two. The internal clock

frequency is 16.348kHz, giving a clock period of

61.04µsec. The total conversion — auto-zero phase,

signal integrate and reference deintegrate — requires

8000 clock periods or 488.3msec. There are approxi-

mately two complete conversions per second.

The integration time is fixed at 1638.5 clock periods or

100msec. This gives rejection of 50/60Hz AC line

noise.

The maximum reference de-integrate time, represent-

ing a full scale analog input, is 3000 clock periods or

183.1msec during manual extended resolution opera-

tion. The 3000 counts are available in Manual mode,

extended resolution operation only. In Auto-Ranging

mode, the maximum de-integrate time is 2000 clock

periods. The 1000 clock periods are added to the auto-

zero phase. An auto-ranging, or manual conversion

takes 8000 clock periods. After a zero crossing is

detected in the Reference De-integrate mode, the auto-

zero phase is entered. Figure 4-1 shows the basic

TC815 timing relationships.

FIGURE 4-1:

BASIC TC815

CONVERSION TIMING

External Crystal = 32.768kHz

Internal Clock Period = TP = 2/32.768 = 61.04µsec

Total Conversion Time = TCONV =8000(TP)

=488.3mec

≈ 2Conv/Sec.

Integration Time = TI = 1638.5 (TP) = 100.0msec.

Maximum Reference De-integration Time =

TDE =3000(TP) = 183.1msec

(Manual Extended Resolution)

Minimum Auto-Zero Time

= (8000-3000-1638.5) (TP)= 205.1msec

(Manual, Extended Resolution)

= (8000-2000-1638.5) (TP)= 266.2msec

(Auto-Range)

Auto-Zero

Phase

Min. Auto-Zero

Time

3361.5TP

TDE

To Input

Signal

TCONV 8000 TP

Fixed

1638.5 TP

*Max

3000.0 TP

Extended

Resolution

Zero Crossing

*In Auto-Range Operation

Maximum is 2000TP and

Minimum Auto-Zero time

i s 4361.5TP

Signal

Integrate

Phase

Reference

De-integrate

Phase

Next Conversion

Auto-Zero Cycle

TC815

TC815 датащи(PDF) 11 Page - Microchip Technology

TC815 датащи(HTML) 11 Page - Microchip Technology

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

датащи скачать

ссылки URL