TC520 MICROCHIP [Microchip Technology], TC520 Datasheet - Page 7

• Manufacturer Part Number: TC520
• Description: Serial Interface Adapter for TC500 A/D Converter Family
• Manufacturer: MICROCHIP [Microchip Technology]

4.0
4.1
The TC500/TC500A/TC510/TC514 data sheet details
the equations necessary to calculate values for integra-
tion resistor (R
(C
erence (V
TC520A, except Integration time (T
time (T
(timebase frequency and LOAD VALUE). Microchip
offers a ready-to-use TC5XX A/D converter design tool.
The TC500 Design Spreadsheet is an Excel-based
spreadsheet that calculates values for all components
as well as the TC520A LOAD VALUE. It also calculates
overall converter performance such as noise rejection,
converter speed, etc.
4.2
Initialization of the TC520A consists of:
1.
2.
4.3
The TC520A powers up with A,B = 00 (IZ Phase),
awaiting a high logic state on CMPTR, which must be
initiated by forcing the TC520A into the AZ phase. This
can be accomplished in one of two ways:
1.
2.
4.4
The LOAD VALUE is the preset value (high byte of the
SYSCLK timing counter) which determines the number
of counts allocated to the AZ and INT phases of
conversion. This value can be calculated using either
the TC520A spreadsheet within the TC500 Design
Spreadsheet software or can be setup as shown in the
following sections.
4.4.1
Choose the TC5XX A/D converter reference voltage
(V
voltage. For example, if V
1.25V. This forces the maximum de-integration time
(T
time (T
during DINT.
©
DEINT
2002 Microchip Technology Inc.
REF
AZ
Power-On RESET of the TC500/TC520A (forc-
ing the TC520A into an AZ phase).
Initializing the TC520A LOAD VALUE.
External hardware (processor or logic) can
momentarily pull LOAD or CE low for a minimum
of 100msec (T
A .01µF RESET capacitor can be connected
from CE to V
CE.
) and reference capacitors (C
) to be half of the maximum A/D converter input
AZ
INT
) to be equal to twice the maximum integration
TYPICAL APPLICATIONS
TC500 Series A/D Converter
Component Selection
Power-On RESET
LOAD VALUE Initialization
), which are functions of the SYSCLK period
TC520A Initialization
), ensuring a full count (maximum resolution)
REF
SELECT V
). All equations apply when using the
INT
CC
) and capacitor (C
AZI
to generate a power-on pulse on
) or;
REF
IN(
, T
MAX
DEINT
)
= 2.5V, choose V
REF
INT
) and voltage ref-
) and Auto zero
INT
), auto zero
REF
=
4.4.2
The TC520A counter length is 16-bits (65536), allowing
the full 65536 counts for T
T
4.4.3
SYSCLK frequency directly affects conversion time.
The faster the SYSCLK, the faster the conversion time.
The upper limit SYSCLK frequency is determined by
the worst case delay of the TC500 comparator (which
for the TC500 and TC500A is 3.2µsec). While a faster
value for SYSCLK can be used, operation is optimized
(error minimized) by choosing a SYSCLK period (1/
SYSCLK frequency) that is greater than 3.2µsec.
Choosing T
quency equal to 250kHz. This makes the external
crystal (or frequency source) equal to 1.0MHz, since
SYSCLK = crystal frequency/4). Calculating integration
time (in msec) using T
32768 = 131msec.
4.4.4
Plug the T
convert the resulting value to hexadecimal:
EQUATION 4-1:
In this example, LOAD VALUE = 128
fore, a LOAD VALUE of 10H is loaded into the TC520A.
If the desired T
the LOAD VALUE would be 9EH, and so on. The
TC520A LOAD VALUE must be initialized on power-up,
and can be re-initialized as often as desired thereafter.
This is accomplished by bringing the LOAD input low
while transmitting the appropriate LOAD VALUE to the
TC520A as shown in Figure 4-1 and Figure 4-2.
4.4.5
The TC520A can be accessed at any time by the host
processor. This makes operation in a polled environ-
ment especially easy since the most recently converted
data is available to the processor as needed. The
TC520A can also be used in an interrupt environment
by connecting DV to the IRQ line of the processor.
Since AZ is the first phase of a new conversion cycle,
the most recently converted data will be available as
soon as DV goes low. If so desired, the interrupt service
routine can also modify the LOAD VALUE during the
DV = low interval.
INT
= 65536/2 or 32768.
LOAD VALUE =
INT
SYSCLK
CALCULATE T
SELECT SYSCLK FREQUENCY
CALCULATE LOAD VALUE
POLLED VS. INTERRUPT
OPERATION
and T
INT
SYSCLK
was 100msec instead of 131msec,
= 4µsec makes the SYSCLK fre-
SYSCLK
[(65536 - (T
DEINT
values into the equation and
INT
= 4µsec, T
results in a maximum
256
TC520A
INT
(10)
/T
DS21431B-page 7
SYSCLK
= 10H. There-
INT
= 4µsec x
)]