MAX1447 Datasheet, PDF (12/24 Pages) Maxim Integrated Products – 3.5- and 4.5-Digit, Single-Chip ADCs with LED Drivers

3.5- and 4.5-Digit, Single-Chip ADCs
with LED Drivers
0
-40
-80
-120
-160
-200
0
10 20 30 40 50 60
FREQUENCY (Hz)
Figure 2. Frequency Response of the SINC⁴ Filter (Notch at 50Hz
and 60Hz)
Filter Characteristics
Figure 2 shows the filter frequency response. The
SINC⁴ characteristic -3dB cutoff frequency is 0.228
times the first notch frequency (5Hz). The oversampling
ratio (OSR) for the MAX1496 is 128 and the OSR for the
MAX1447/MAX1498 is 1024.
The output data rate for the digital filter corresponds to
the positioning of the first notch of the filter’s frequency
response. The notches of the SINC⁴ filter are repeated
at multiples of the first notch frequency. The SINC⁴ filter
provides an attenuation of better than 100dB at these
notches. For example, 50Hz is equal to 10 times the
first notch frequency and 60Hz is equal to 12 times the
first notch frequency.
For large step changes at the input, allow a settling
time of 800ms before valid data is read.
Internal Clock
The MAX1447/MAX1496/MAX1498 contain an internal
oscillator. Using the internal oscillator saves board
space by removing the need for an external clock
source. The oscillator is optimized to give 50Hz and
60Hz power-supply and common-mode rejection.
Charge Pump
The MAX1447/MAX1496/MAX1498 contain an internal
charge pump to provide the negative supply voltage
for the internal analog input/reference buffers.
A
F
D
G
DIGIT 4
A
A
A
A
BF _G B F _G BF _G BF _G B
CE
CE
CE
CE
C
DP
DP
DP
DP
DP
D
D
D
D
DIGIT 3
DIGIT 2
DIGIT 1
DIGIT 0
Figure 3. Segment Connection for the MAX1447/MAX1498
(4.5 Digits)
A
F
D
G
DIGIT 3
A
A
A
BF _G B F _G BF _G B
CE
CE
CE
C
DP
DP
DP
DP
D
D
D
DIGIT 2
DIGIT 1
DIGIT 0
Figure 4. Segment Connection for the MAX1496 (3.5 Digits)
Table 1. LED Priority Table
HOLD
1
0
0
X = Don’t care.
PEAK
X
1
0
DISPLAY VALUES FORM
Hold value
Peak value
Latest ADC result
The bipolar input range of the analog input/reference
buffers allows this device to accept negative inputs
with high source impedances. Connect a 0.1µF capac-
itor from VNEG to GND.
LED Driver
The MAX1447/MAX1498 have a 4.5-digit common-cath-
ode display driver, and the MAX1496 has a 3.5-digit
common-cathode display driver. Figures 3 and 4 show
the connection schemes for a standard seven-segment
LED display. The LED update rate is 2.5Hz. The
MAX1447/MAX1496/MAX1498 automatically display the
results of the ADC, if desired (Table 1).
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