TC530 Datasheet, PDF (13/22 Pages) TelCom Semiconductor, Inc – 5V PRECISION DATA ACQUISITION SUBSYSTEMS

5.0 SELECTING COMPONENT
VALUES FOR THE
TC530/TC534
1. Calculate Integrating Resistor (R_INT)
The desired full scale input voltage and amplifier
output current capability determine the value of
R_INT. The buffer and integrator amplifiers each
have a full scale current of 20µA. The value of R_INT
is therefore directly calculated as follows:
EQUATION 5-1:
where:
V_INMAX
R_INT = ₂₀
mΩ
V_IN(MAX) = Maximum Input Voltage (full count voltage)
R_INT = Integrating Resistor (in mΩ)
For loop stability, R_INT should be ≥ 50kΩ.
2. Select Reference (C_REF) and Auto Zero (C_AZ)
Capacitors
C_REF and C_AZ must be low leakage capacitors
(such as polypropylene). The slower the conver-
sion rate, the larger the value C_REF must be. Rec-
ommended capacitors for C_REF and C_AZ are
shown in Table 5-1. Larger values for C_AZ and
C_REF may also be used to limit rollover errors.
TABLE 5-1: C_REF AND C_AZ SELECTION
Conversion Typical Value of
Per Second C_REF, C_AZ (µF)
Suggested* Part
Number
>7
0.1
SMR5 104K50J0IL
2 to 7
0.22
SMR5 224K50J2L
2 or less
0.47
SMR5 474K50J04L
Note: *Manufactured by Evox-Rifa, Inc.
5.1 Calculate Integrating Capacitor
(C_INT)
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_DD
(or V_SS) less 0.9V (i.e.,IV_DD – 0.9VI or IV_SS +0.9VI).
Using the 20µA buffer maximum output current, the
value of the integrating capacitor is calculated using the
following equation.
EQUATION 5-2:
C_INT =(T^{INT) (20 x 10 -6) µF}
(V_S - 0.9)
where: T_INT = Integration Period
V_S = IV_DDI
C_INT = Integrated Capacitor Value (µF).
TC530/TC534
It is critical that the integrating capacitor have a very
low dielectric absorption. PPS capacitors are an exam-
ple of one such dielectric. Table 5-2 summarizes
various capacitors suitable for C_INT.
TABLE 5-2:
RECOMMENDED CAPACITOR
FOR C_INT
Value (µF)
Suggested Part Number*
Note:
0.1
SMR5 104K50J0IL
0.22
SMR5 224K50J2L
0.33
SMR5 334K50J03L4
0.47
SMR5 474K50J04L
*Manufactured by Evox-Rifa, Inc.
5.2 Calculate V_REF
The reference de-integration voltage is calculated
using the following equaton:
EQUATION 5-3:
V_REF = ^{(VS – 0.9) (CINT) (RINT)} _V
2(R_INT)
5.3 Serial Port
Communication with the TC530/TC534 is accom-
plished over a 3 wire serial port. Data is clocked into
D_IN on the rising edge of D_CLK and clocked out of D_OUT
on the falling edge of D_CLK. R/W must be HIGH to read
converted data from the serial port and LOW to write
the LOAD VALUE to the TC530/TC534.
5.4 Data Read Cycle
Data is shifted out of the serial port in the following
order: End of Conversion (EOC), Overrange (OVR),
Polarity (POL), conversion data (MSB first). When R/W
is high, the state of the EOC bit can be polled by simply
reading the state of D_OUT. This allows the processor to
determine if new data is available without connecting
an additional wire to the EOC output pin (this is espe-
cially useful in a polled environment). See Figure 5-1.
FIGURE 5-1:
SERIAL PORT DATA
READ CYCLE
R/W
D_CLK
DOUT
EOC OVR POL MSB LSB
© 2002 Microchip Technology Inc.
DS21433B-page 13