tc500a Microchip Technology Inc., tc500a Datasheet - Page 12

• Manufacturer Part Number: tc500a
• Description: Precision Analog Front Ends
• Manufacturer: Microchip Technology Inc.

TC500/A/510/514
7.0
7.1
The procedure outlined below allows the user to arrive
at values for the following TC5XX design variables:
1.
2.
3.
4.
7.2
Integration time must be picked as a multiple of the
period of the line frequency. For example, T
33 msec, 66 msec and 132 msec maximize 60 Hz line
rejection.
7.3
The duration of the DINT phase is a function of the
amount of voltage stored on the integrator during T
and the value of V
immediately following INT and terminated when an inte-
grator output zero-crossing is detected. In general, the
maximum number of counts chosen for DINT is twice
that of INT (with V
7.4
The desired full-scale input voltage and amplifier output
current capability determine the value of R
buffer and integrator amplifiers each have a full-scale
current of 20 A.
The value of R
following equation:
EQUATION 7-1:
7.5
C
polypropylene). The slower the conversion rate, the
larger the value C
capacitors for C
Larger values for C
limit rollover errors.
DS21428D-page 12
Where:
V
R
For loop stability, R
REF
IN(MAX)
INT
Integration Phase Timing.
Integrator Timing Components (R
Auto-zero and Reference Capacitors.
Voltage Reference.
and C
= Integrating Resistor (in M )
TYPICAL APPLICATIONS
Component Value Selection
Select Integration Time
DINT and IZ Phase Timing
Calculate Integrating Resistor
(R
Select Reference (C
zero (C
= Maximum input voltage (full count voltage)
AZ
INT
INT
must be low leakage capacitors (such as
R
)
INT
REF
REF
REF
is, therefore, directly calculated in the
AZ
AZ
INT
in M
. The DINT phase must be initiated
and C
) Capacitors
REF
chosen at V
and C
should be
must be. Recommended
AZ
=
REF
are shown in Table 7-1.
V
---------------------- -
IN MAX
IN(MAX)
may also be used to
20
REF
50 k .
INT
) and Auto-
, C
/2).
INT
INT
INT
).
times of
. The
INT
TABLE 7-1:
7.6
The integrating capacitor must be selected to maximize
integrator output voltage swing. The integrator output
voltage swing is defined as the absolute value of V
(or V
Using the 20 A buffer maximum output current, the
value of the integrating capacitor is calculated using the
following equation.
EQUATION 7-2:
It is critical that the integrating capacitor has a very low
dielectric absorption. Polypropylene capacitors are an
example of one such dialectic. Polyester and poly-
bicarbonate capacitors may also be used in less critical
applications. Table 7-2 summarizes recommended
capacitors for C
TABLE 7-2:
7.7
The reference de-integration voltage is calculated
using the following equation:
EQUATION 7-3:
* Manufactured by Evox Rifa, Inc.
* Manufactured by Evox Rifa, Inc.
Where:
T
V
V
Conversions
Per Second
INT
S
S
2 or less
= IV
= IV
SS
2 to 7
= Integration Period
>7
) less 0.9V (i.e., IV
DD
DD
Calculate Integrating Capacitor
(C
Calculate V
Value
V
I or IV
I (TC510, TC514)
0.22
0.33
0.47
INT
0.1
REF
C
)
INT
INT
SS
=
Typical Value of
C
RECOMMENDED CAPACITOR
FOR C
C
.
I, whichever is less (TC500/A)
---------------------------------------------------------- - V
REF
REF
=
V
S
-------------------------------------------- -
, C
0.22
0.47
–
0.1
T
© 2006 Microchip Technology Inc.
REF
AND C
INT
0.9
AZ
INT
DD
2 R
V
( F)
SMR5 104K50J01L4
SMR5 224K50J02L4
SMR5 334K50J03L4
SMR5 474K50J04L4
S
C
- 0.9VI or IV
20 10
–
INT
INT
0.9
AZ
Part Number*
SMR5 104K50J01L4
SMR5 224K50J02L4
SMR5 474K50J04L4
Suggested
SELECTION
R
Suggested* Part
6 –
INT
Number
SS
+ 0.9VI).
DD