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TC530/TC534
DS21433C-page 12
2007 Microchip Technology Inc.
5.0
TYPICAL APPLICATIONS
5.1
Programming the TC530/TC534
5.1.1
AZ AND INT PHASE DURATION
These two phases have equal duration determined by
the crystal (or external) frequency and the timer initial-
ization byte (LOAD VALUE). Timing is selected as
follows:
1.
Select Integration Time
Integration time must be picked as a multiple of
the period of the line frequency. For example,
TINT times of 33 ms, 66 ms and 132 ms
maximize 60 Hz line rejection.
2.
Estimate Crystal Frequency
Crystal frequencies as high as 2 MHz are
allowed. Crystal frequency is estimated using:
EQUATION 5-1:
3.
Calculate LOAD VALUE
EQUATION 5-2:
FIN can be adjusted to a standard value during this
step. The resulting base, -10 LOAD VALUE, must be
converted to a hexadecimal number and then loaded
into the serial port prior to initiating A/D conversion.
5.2
DINT and IZ Phase Timing
The duration of the DINT phase is a function of the
amount of voltage stored on the integrator capacitor
during INT and the value of VREF. The DINT phase is
initiated immediately following INT and terminated
when an integrator output zero crossing is detected. In
general, the maximum number of counts chosen for
DINT is twice that of INT (with VREF chosen at
VIN(MAX)/2).
5.3
System RESET
The TC530/TC534 must be forced into the AZ state
when power is first applied. A .01 F capacitor
connected from RESET to VDD (or external system
reset logic signal) can be used to momentarily drive
RESET high for a minimum of 100 ms.
5.4
Design Example
application. Timing and component values are
calculated from equations and recommendations made
of this document. The EOC connection to the
processor INT input is for interrupt-driven applications
only. (In polled systems, the EOC output is available on
DOUT).
Given:
1.
Pick Integration time (TINT): 66 ms.
2.
Estimate crystal frequency.
EXAMPLE 5-1:
3.
Calculate LOAD VALUE
EXAMPLE 5-2:
4.
Calculate RINT.
EXAMPLE 5-3:
5.
Calculate CINT for maximum (4V) integrator out-
put swing:
2(RES)/TINT
Where:
RES
=
Desired Converter Resolution (in
counts)
FIN
=
Input Frequency (in MHz)
INT
=
Integration Time (in seconds)
[LOAD VALUE]10
256
TINT
() F
IN
()
1024
------------------------------
–
=
Required Resolution
(RES):
16-bits (65,536 counts.)
Maximum: VIN ±2V
Power Supply Voltage: +5V
60Hz System
FIN
2RES
TINT
------------
2 65536
66ms
----------------------- 2MHz
≈
==
LOAD VALUE
256
TINT
() F
IN
()
1024
------------------------------
–
128
[]
10
==
128
[]
10
80 hex
=
RINT
VINMAX
20
-------------------
2
20
------
100k
Ω
==
=