TC500 datasheet(14/28 Pages) MICROCHIP

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TC500/A/510/514

DS21428B-page 14

8.0

DESIGN EXAMPLE

(SEE FIGURES 8-1 TO 8-4)

Given:

Required Resolution: (16 Bits (65,536

counts).

Maximum VIN:±2V

Power Supply Voltage: +5V

60Hz System

Step 1: Pick integration time (tINT) as a multiple of the

line frequency:

1/60Hz = 16.6msec. Use 4x line frequency

=66msec

Step 2: Calculate RINT

RINT =VIN(MAX) /20µA2 /20µA = 100kΩ

Step 3: Calculate CINT for maximum (4V) integrator

output swing:

CINT =(tINT)(20 x10

–6)/(V

S -0.9)

= (.066) (20 x 10 –6)/ (4.1)

= .32µF (use closest value: 0.33µF)

Note:

Microchip recommended capacitor:

Evox-Rifa p/n: 5MR5 334K50J03L4.

Step 4: Choose CREF and CAZ based on conversion

rate:

Conversions/sec:

=1/(TAZ +TINT +2TINT +2msec)

= 1/(66msec +66msec

+132msec +2msec)

= 3.7 conversions/sec

From which CAZ =CREF =0.22µF

(see Table 6-1)

Note:

Microchip recommended capacitor:

Evox-Rifa p/n: 5MR5 224K50J02L4

Step 5: Calculate VREF

EQUATION 8-1:

(VS -0.9) (CINT)(RINT)

VREF =

2(TINT)

=(4.1) (0.33x1–6)(105) / 2(.066)

= 1.025V

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