Evaluate: MAX1282
MAX1282 Evaluation Kit/Evaluation System
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Detailed Description
MAX1282 Stand-Alone EV Kit
The MAX1282 EV kit provides a proven PCB layout to
evaluate the MAX1282. It must be interfaced to appropri-
ate timing signals for proper operation. Connect +5V to
VDD, and connect ground return to GND (Figure 1). Refer
to the MAX1282 IC data sheet for timing requirements.
MAX1282 EV System
The MAX1282 EV system operates from a user-supplied
7VDC to 20VDC power supply. Windows 98/2000/XP-
compatible software running on a PC interfaces to the
EV system board through the computer’s serial commu-
nications port (virtual COM port). See the
Quick Start
section for set-up and operating instructions.
Description of Software
The evaluation software’s main window controls the seri-
al clock speed and sample rate. It displays the voltage
and output code, as well as some input signal statistics.
A separate graph window shows the data changing in
real time. The update rate is limited to about 10 samples
per second, due to COM port bandwidth limitations.
Controls
The control word is divided into several fields. To
change the active control word, drop down the appro-
priate field’s combo box and select the desired option.
If the QSPI™ clock is set to STOP, then configuration
data will not be sent until the READ button is pressed.
Statistics
The Minimum and Maximum fields show the highest
and lowest readings acquired. The Average field shows
a running mean. The Clear button resets the statistics.
To remove offset errors, first apply 0V to the active input
channel, clear statistics, acquire some samples, and
then check Tare. This average offset voltage will now be
subtracted from all subsequent measurements.
Sampling
Choose the desired sampling rate (QSPI clock), sampling
size (Sample! menu item), and press Begin Sampling!
(in Sample! pop-up window). Sample size is restricted to a
power of two to permit FFT processing once the data is
saved to a file. After the samples have been collected, the
data is automatically uploaded to the host and is graphed.
Once displayed, the data can optionally be saved to a file.
Saving Graphs to Disk
Data in the real-time graph and in sampled data graphs
may be saved to a file. Only the raw output codes are
saved, but voltages may be inferred, based on the ref-
erence voltage and the maximum code value.
Scanning All Channels Input Signal
To scan through all channels, select SCAN from the
Input menu.
Evaluating Shutdown
The evaluation software configures the 68HC16’s QSPI
submodule to continuously read data from the
MAX1282 into the 68HC16. The sample rate is con-
trolled by the QSPI clock. To evaluate power-saving
modes, these automatic updates must be stopped.
First, set the QSPI clock control to STOP. This reconfig-
ures the 68HC16’s QSPI submodule to stop driving the
serial clock. Second, in the evaluation software’s main
window, uncheck the Read Every...msec check-box.
Next, choose the desired software power-down control
word, and press the Read button to send the new con-
figuration to the MAX1282. If evaluating the hardware
shutdown, move jumper JU2 to the 2-3 position.
Reference Voltage
The evaluation software assumes a 2.5V reference volt-
age, unless otherwise specified. Refer to the MAX1282
IC data sheet for more information. To override this
value, type the new reference voltage into the Vref edit
box and press the Set Vref button. Note: This new
V
REF
value is used only by the evaluation software and
does not physically change the reference voltage.
Description of Hardware
U1, the MAX1282, is a high-speed, multichannel, 12-bit
data-acquisition system. Resistors R1–R4 and capacitors
C1–C4 form single-pole, lowpass anti-aliasing filters with
a nominal 3µs time constant and a corner frequency of
approximately 50kHz. C9 and C10 bypass the ADC’s
voltage reference and reference buffer. When plugged
into the 68HC16MODULE, the VDD circuit is powered by
+5V. (See Figure 1 and refer to the MAX1282 data sheet.)
Troubleshooting
Problem: No output measurement. System seems to
report zero voltage or fails to make a measurement.
Check the VDD supply voltage. Check the reference
voltage using a digital voltmeter (DVM). Use an oscillo-
scope to verify that the conversion-start signal is being
strobed. Verify that SHDN is being driven high.
Problem: Measurements are erratic, unstable; poor
accuracy.
Check the reference voltage using a DVM. Use an
oscilloscope to check for noise. When probing for
noise, keep the oscilloscope ground return lead as
short as possible, preferably less than 1/2in (10mm).
QSPI is a trademark of Motorola, Inc.
