TC500_06 Datasheet, PDF (15/34 Pages) Microchip Technology – Precision Analog Front Ends

9.0 DESIGN EXAMPLES
Refer to Figures 9-1 to 9-4.
Given:
Step 1.
Step 2.
Step 3.
Note:
Step 4.
Note:
Step 5.
Required Resolution: 16 bits (65,536
counts).
Maximum V_IN: ±2V
Power Supply Voltage: +5V
60 Hz System
Pick integration time (t_INT) as a multiple
of the line frequency:
1/60 Hz = 16.6 msec. Use 4x line
frequency.
= 66 msec
Calculate R_INT:
R_INT = V_IN(MAX) /20 μA 2 /20 μA
= 100 kΩ
Calculate C_INT for maximum (4V)
integrator output swing.
C_INT = (t_INT) (20 x 10 ^–6) / (V_S - 0.9)
= (.066) (20 x 10 ^–6) / (4.1)
= 0.32 μF (use closest value: 0.33 μF)
Microchip recommended capacitor:
Evox Rifa p/n: 5MR5 334K50J03L4.
Choose C_REF and C_AZ based on
conversion rate.
Conversions/sec:
= 1/(T_AZ + T_INT + 2 T_INT + 2 msec)
= 1/(66 msec +66 msec
+132 msec +2 msec)
= 3.7 conversions/sec
From which C_AZ = C_REF = 0.22 μF
(see Table 7-1)
Microchip recommended capacitor:
Evox Rifa p/n: 5MR5 224K50J02L4
Calculate V_REF:
EQUATION 9-1:
V_REF
=
-⁽--^V----^S----–----⁰---^.--⁹---⁾--⁽---^C----^I--^N----^T---⁾--⁽--^R----^I--^N----^T---⁾
2(T_INT)
=-------(_--4_---._--1_---)_---(_--0_---._--3_---3_----×_-----1_---^–_---⁶_--)_---(_--1_---0_---⁵_----)
2 ( 0.66 )
= 1.025
TC500/A/510/514
© 2006 Microchip Technology Inc.
DS21428D-page 15