TC500ACPF datasheet(19/38 Pages) MICROCHIP

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DS21428E-page 19

TC500/A/510/514

9.0

DESIGN EXAMPLES

Refer to Figures 9-1 to 9-4.

EQUATION 9-1:

Given:

Required Resolution: 16 bits (65,536

counts).

Maximum VIN: ±2V

Power Supply Voltage: +5V

60 Hz System

Step 1.

Pick integration time (tINT) as a multiple

of the line frequency:

1/60 Hz = 16.6 ms. Use 4x line

frequency.

= 66 ms

Step 2.

Calculate RINT:

RINT = VIN(MAX) /20 μA 2 /20 μA

= 100 kΩ

Step 3.

Calculate CINT for maximum (4V)

integrator output swing.

CINT = (tINT) (20 x 10 –6) / (VS - 0.9)

= (.066) (20 x 10 –6) / (4.1)

= 0.32 μF (use closest value: 0.33 μF)

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 + 2 TINT + 2 ms)

= 1/(66 ms +66 ms +132 ms +2 ms)

= 3.7 conversions/sec

From which CAZ = CREF = 0.22 μF

(see Table 7-1)

Note:

Microchip recommended capacitor:

Evox Rifa p/n: 5MR5 224K50J02L4

Step 5.

Calculate VREF:

REF

0.9

–

() C

INT

() R

INT

()

INT

()

-----------------------------------------------------------

4.1

() 0.33 10

–

() 100 10

()

2 66

–

()

--------------------------------------------------------------------------

1.025 V

()

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