5V PRECISION DATA ACQUISITION
SUBSYSTEMS
1
2
3
4
5
6
7
8
TC530
TC534
(2) Improper sequencing of the power supply inputs
(VDD vs. VCCD) can potentially cause an improper power-up
sequence to occur in the internal state machines. It is
recommended that the digital supply, VCCD, be powered up
first. Onemethodofinsuringthecorrectpower-upsequence
is to delay the analog supply using a series resistor and a
capacitor. See Figure 6, TC530/534 Typical Application.
(6) Circuit assemblies should be scrupulously clean to
prevent the presence of contamination from assembly,
handling, or the cleaning itself. Minutely conductive trace
contaminates, easily ignored in most applications, can ad-
versely affect the performance of high impedance circuits.
The input and integrator sections should be made as com-
pact and close to the TC53x as possible.
(3) Decoupling capacitors, preferably a higher value elec-
trolytic or tantulum in parallel with a small ceramic or
tantalum, should be used liberally. This includes bypassing
the supply connections of all active components and the
voltage reference.
(7) Digital and other dynamic signal conductors should be
keptasfarfromtheTC53x’sanalogsectionaspossible. The
microcontroller or other host logic should be kept quiet
during a measurement cycle. Background activites such as
keypad scanning, display refreshing, and power switching
can introduce noise.
(4) Critical components should be chosen for stability and
low noise. The use of a metal-film resistor for RINT and
Polypropylene or Polyphenelyne Sulfide (PPS) capacitors
for CINT, CAZ, and CREF is highly recommended.
TC530EV Evaluation Kit
TheTC530EVconsistsofa4"x6"pre-assembledcircuit
board that connects to the serial port of any PC or dumb
terminal. Also included is a WindowsTM* ExcelTM*-based
design utility that calculates component and LOAD values
based on user input, and prints a finished circuit schematic.
Please contact your local TelCom representative for more
information,orpointyourwebbrowsertohttp://www.telcom-
semi.com.
(5) The inputs and integrator section are very high imped-
ance nodes. Leakage to or from these critical nodes can
contributemeasurementerror. Aguard-ringshouldbeused
to protect the integrator section from stray leakage.
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TELCOM SEMICONDUCTOR, INC.
3-59
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
