Rainbow Electronics MAX1499 User Manual
Page 15
MAX1497/MAX1499
3.5- and 4.5-Digit, Single-Chip ADCs with LED
Drivers and µC Interface
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15
Leading-Zero Suppression
The MAX1497/MAX1499 include a leading-zero sup-
pression circuitry to turn off unnecessary zeros. For
example, when DPSET1 and DPSET2 = [0,0], 0.0 is dis-
played instead of 000.0. This feature saves a substan-
tial amount of power from being wasted.
Interdigit Blanking
The MAX1497/MAX1499 also include an interdigit
blanking circuitry. Without this feature, it is possible to
see a faint digit next to a digit that is completely on. The
interdigit blanking circuitry prevents bleeding over into
the next digit for a short period of time. The typical
interdigit blanking time is 4µs.
Reference
The MAX1497/MAX1499 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
the RANGE bit equal to zero. With the RANGE bit set to
one, the full-scale range is ±200mV. A decreased refer-
ence voltage decreases full-scale range (see the
Transfer Functions section).
The MAX1497/MAX1499 accept either an external ref-
erence or an internal reference. The INTREF bit selects
the reference mode (see the Control Register
(Read/Write) section).
For internal reference operation, set the INTREF bit to
one, connect 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.
The default power-on state sets the MAX1497/
MAX1499 to use the external reference with the INTREF
bit cleared to zero. The external reference inputs, REF+
and REF-, are fully differential. For a valid external refer-
ence input, V
REF+
must be greater than V
REF-
. Bypass
REF+ and REF- with a 0.1µF or greater capacitor to
GND in external reference mode.
Figure 16 shows the MAX1497/MAX1499 operating with
an external single-ended reference. In this mode, REF-
is connected to GND and REF+ is driven with an exter-
nal 2.048V reference. Bypass REF+ to GND with a
0.47µF capacitor.
1
4
3
2
1
0
4
3
2
0
4
T
T
ON
DIGIT 4 (MSD)
DIGIT 3
DIGIT 2
DIGIT 1
DIGIT 0 (LSD)
DATA
MSD
LSD
Figure 6. LED Voltage Waveform—MAX1499
3
3
2
1
0
3
2
1
0
2
1
T
T
ON
DIGIT 3 (MSD)
DIGIT 2
DIGIT 1
DIGIT 0 (LSD)
DATA
MSD
LSD
Figure 7. LED Voltage Waveform—MAX1497