MAX1367 Maxim Integrated Products, MAX1367 Datasheet - Page 16

• Manufacturer Part Number: MAX1367
• Description: (MAX1365 / MAX1367) Digit Panel Meters
• Manufacturer: Maxim Integrated Products

During these 6s, the MAX1365 displays 1.2V to 1.5V
when a stable reference is detected. If a valid refer-
ence is not found, the MAX1365 times out after 6s and
begins enhanced offset calibration. Enhanced offset
calibration typically lasts 2s. The MAX1365 begins con-
verting after enhanced offset calibration.
The MAX1365/MAX1367 reference sets the full-scale
range of the ADC transfer function. With a nominal
2.048V reference, the ADC full-scale range is ±2V with
RANGE = GND. With RANGE = DV
range is ±200mV. A decreased reference voltage
decreases full-scale range (see the Transfer Functions
section).
The ADC of the MAX1365/MAX1367 can accept either
an external reference or an internal reference (INTREF).
The INTREF logic selects the reference mode. For inter-
nal-reference operation, set INTREF to DV
REF- to GND, and bypass REF+ to GND with a 4.7µF
capacitor. The internal reference provides a nominal
2.048V source between REF+ and GND. The internal-
reference temperature coefficient is typically
40ppm/°C.
For external-reference operation, set INTREF to GND.
REF+ and REF- are fully differential. For a valid exter-
nal-reference input, VREF+ must be greater than VREF-.
Bypass REF+ and REF- with a 0.1µF or greater capaci-
tor to GND in external-reference mode.
Figure 6 shows the MAX1365/MAX1367 operating with
an external differential reference. In this figure, REF- is
connected to the top of the strain gauge and REF+ is
connected to the midpoint of the resistor-divider of
the supply.
The DAC of the MAX1365/MAX1367 accept either an
external reference or an internal reference. The REFSELE
enables or disables the internal reference. For external-
reference operation, disable the DAC reference buffer by
setting REFSELE to DV
to REF_DAC.
For internal-reference operation, enable the DAC refer-
ence buffer by setting REFSELE to GND. In this mode,
leave REFDAC floating.
In either internal or external reference operation,
bypass REF_DAC with a 0.1µF capacitor to GND.
Choose a reference with output impedance (load regu-
lation equivalent) of 100mΩ or less, such as the
MAX6126. For best performance, use an external
reference source for the ADC and DAC.
Stand-Alone, 4.5-/3.5-Digit Panel Meters
with 4–20mA Output
16
______________________________________________________________________________________
DD
and connect a voltage source
DD,
ADC Reference
DAC Reference
the full-scale
Reference
DD,
connect
For the MAX1365/MAX1367, a voltage proportional to
the ADC input is available at DACVOUT. Connect
DACVOUT to CONV_IN for normal operation. See
Figure 11 for the DAC transfer function.
The MAX1365/MAX1367 offer on-chip offset calibration.
The device offset calibrates during every conver-
sion cycle.
Enhanced offset calibration is a more accurate calibra-
tion method that is needed in the case of the ±200mV
range and 4.5-digit resolution. In addition to enhanced
offset calibration at power-up, the MAX1365/MAX1367
perform enhanced calibration on demand by connect-
ing HOLD to AV
The MAX1365/MAX1367 feature peak-detection circuitry.
When activated, the devices display only the highest
voltage measured to the LED. First, the current ADC
result is displayed. The new ADC conversion result is
compared to the current result. If the new value is larg-
er than the previous peak value, the new value is dis-
played. If the new value is less than the previous peak
value, the display remains unchanged. Connect PEAK
to GND to clear the peak value and disable the peak
function. See Table 1 for LED Display priority.
The MAX1365/MAX1367 feature data-hold circuitry.
When activated, the device holds the current reading
on the LED.
Connect the differential inputs of the MAX1365/
MAX1367 to the bridge network of the strain gauge. In
Figure 6, the analog supply voltage powers the bridge
network and the MAX1365/MAX1367, along with the
reference voltage. The MAX1365/MAX1367 handle an
analog input voltage range of ±200mV and ±2V full
scale. The analog/reference inputs of the parts allow
the analog input range to have an absolute value of
anywhere between -2.2V and +2.2V.
DD
Enhanced Offset Calibration
for > 2s.
Strain-Gauge Measurement
Offset Calibration
DAC Operation
Peak
Hold