MAX1497 Maxim, MAX1497 Datasheet - Page 27

• Manufacturer Part Number: MAX1497
• Description: 3.5- and 4.5-Digit / Single-Chip ADCs with LED Drivers and C Interface
• Manufacturer: Maxim

The transfer function for the MAX1499 with AIN+ - AIN-
≥ 0, RANGE = 1 is:
The transfer function for the MAX1499 with AIN+ - AIN-
< 0, RANGE = 1 is:
The transfer function for the MAX1497 with AIN+ - AIN-
≥ 0, RANGE = 1 is:
Figure
Table 6. Segment Current Selection
COUNTS
COUNTS
- 1 - - -
LED
1 - - -
-1999
COUNTS
1999
COUNTS
- 0
- 1
- 2
19. MAX1497 Transfer Function, ±200mV Range
2
1
0
R
3.5- and 4.5-Digit, Single-Chip ADCs with LED
ADC RESULT
ISET
>2500
7CFh
7CFh
002h
001h
000h
FFFh
FFEh
FFDh
830h
<830h
100
500
25
50
=
(kΩ)
=
1 024
=
=
.
1 024
.
1 024
1 024
.
.
-200mV
______________________________________________________________________________________






V
V
REF
V
AIN
V






REF
AIN
V
V
V
V
REF
+
+
REF
AIN
AIN
+
+
−
−
ANALOG INPUT VOLTAGE
+
+
V
V
−
−
+
+
REF
AIN
-100µV 100µV
V
V
−
−
−
−
REF
AIN
V
V
LED driver disabled
V
V
REF
AIN
−
REF
−
AIN
−
0
−
−
−
×

 ×

I
−
SEG
−
×
20 000
21.6
10.8
×
5.4
1.1
,
2000
(mA)
20 000
2000
,

 ×


 ×

+200mV

 +

×
10
10
10
1
+
1
Drivers and µC Interface
The transfer function for the MAX1497 with AIN+ - AIN-
< 0, RANGE = 1 is:
Power up AVDD and DVDD (MAX1499) and VDD
(MAX1497) before applying an analog input and exter-
nal reference voltage to the device. If this is not possi-
ble, limit the current into these inputs to 50mA. When
the analog and digital supplies come from the same
source, isolate the digital supply from the analog sup-
ply with a low-value resistor (10Ω) or ferrite bead. For
best performance, ground the MAX1497/MAX1499 to
the analog ground plane of the circuit board.
Avoid running digital lines under the device, because
they may couple noise onto the die. Run the analog
ground plane under the MAX1497/MAX1499 to mini-
mize coupling of digital noise. Make the power-supply
lines to the MAX1497/MAX1499 as wide as possible to
provide low-impedance paths and reduce the effects of
glitches on the power-supply line.
Shield fast-switching signals, such as clocks, with digital
ground to avoid radiating noise to other sections of the
board. Avoid running clock signals near the analog
inputs. Avoid crossover of digital and analog signals.
Running traces that are on opposite sides of the board
at right angles to each other reduces feedthrough
effects. A microstrip technique is best, but is not always
Figure
COUNTS
- 1 - - -
LED
1 - - -
-1999
1999
- 0
- 1
- 2
20. MAX1497 Transfer Function, ±2V Range
2
1
0
ADC RESULT
>7CFh
7CFh
002h
001h
000h
FFFh
FFEh
FFDh
830h
<830h
=
Supplies, Layout, and Bypassing
1 024
.
-2V



V
V
REF
AIN
+
+
ANALOG INPUT VOLTAGE
−
−
V
V
-1mV
REF
AIN
0
−
−
1mV
×
2000

 ×

+2V
10
+
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