TC500/A/510/514
TABLE 6-1:
C
AND C SELECTION
AZ
6.0
6.1
TYPICAL APPLICATIONS
Component Value Selection
REF
Conversions Typical Value of
Per Second
Suggested* Part
Number
C
REF, CAZ (µF)
The procedure outlined below allows the user to arrive
at values for the following TC5XX design variables:
>7
0.1
SMR5 104K50J01L4
SMR5 224K50J02L4
SMR5 474K50J04L4
2 to 7
0.22
0.47
1. Integration Phase Timing
2 or less
2. Integrator Timing Components (R , C
)
INT INT
Note:
Manufactured by Evox-Rifa, Inc.
3. Auto Zero and Reference Capacitors
4. Voltage Reference
6.6
Calculate Integrating Capacitor
(CINT
)
6.2
Select Integration Time
The integrating capacitor must be selected to maximize
integrator output voltage swing. The integrator output
Integration time must be picked as a multiple of the
period of the line frequency. For example, T times of
33msec, 66msec and 132msec maximize 60Hz line
rejection.
INT
voltage swing is defined as the absolute value of V
DD
(or V ) less 0.9V (i.e., IV - 0.9VI or IV + 0.9VI).
SS
DD
SS
Using the 20µA buffer maximum output current, the
value of the integrating capacitor is calculated using the
following equation.
6.3
DINT and IZ Phase Timing
The duration of the DINT phase is a function of the
amount of voltage stored on the integrator during T
EQUATION 6-2:
INT
and the value of V
. The DINT phase must be initi-
-6
REF
(T ) (20 x 10
)
INT
ated immediately following INT and terminated when
an integrator output zero-crossing is detected. In gen-
eral, the maximum number of counts chosen for DINT
µF
C
=
INT
(V - 0.9)
S
Where:
is twice that of INT (with V
chosen at V
/2).
REF
IN(MAX)
T
= Integration Period
INT
6.4
Calculate Integrating Resistor
(RINT
V
V
= IV I or IV I, whichever is less (TC500/A
DD SS
S
S
)
= IV I (TC510, TC514)
DD
The desired full scale input voltage and amplifier output
It is critical that the integrating capacitor has a very low
dielectric absorption. Polypropylene capacitors are an
example of one such dielectic. Polyester and Polybicar-
bonate capacitors may also be used in less critical
applications. Table 6-2 summarizes recommended
current capability determine the value of R . The
INT
buffer and integrator amplifiers each have a full-scale
current of 20µA.
The value of R
is therefore directly calculated in the
INT
following equation:
capacitors for C
.
INT
EQUATION 6-1:
TABLE 6-2:
RECOMMENDED CAPACITOR
FOR C
V
INT
IN(MAX)
R
(in MΩ) =
INT
20
Value
Suggested Part Number*
0.1
SMR5 104K50J01L4
SMR5 224K50J02L4
SMR5 334K50J03L4
SMR5 474K50J04L4
Where:
0.22
0.33
0.47
V
= Maximum input voltage (full count voltage)
IN(MAX)
R
= Integrating Resistor (in MΩ)
INT
For loop stability, R
should be ≥ 50kΩ.
INT
Note:
Manufactured by Evox-Rifa, Inc.
6.5
Select Reference (CREF) and Auto
Zero (CAZ) Capacitors
6.7
Calculate VREF
The reference deintegration voltage is calculated using
the following equation:
C
and C must be low leakage capacitors (such as
REF
AZ
polypropylene). The slower the conversion rate, the
larger the value C must be. Recommended capac-
REF
EQUATION 6-3:
itors for C
and C are shown in Table 6-1. Larger
REF
AZ
(V – 0.9) (C ) (R )
INT
S
INT
values for C
rollover errors.
and C
may also be used to limit
REF
AZ
V
=
V
REF
2(R
)
INT
2002 Microchip Technology Inc.
DS21428B-page 11
MICROCHIP [ MICROCHIP ]
