MAX1253 Datasheet, PDF (27/29 Pages) Maxim Integrated Products – Stand-Alone, 10-Channel, 12-Bit System Monitors with Internal Temperature Sensor and VDD Monitor

Stand-Alone, 10-Channel, 12-Bit System Monitors
with Internal Temperature Sensor and V_DD Monitor
OUTPUT CODE
011....111
011....110
000....010
000....001
000....000
111....111
111....110
111....101
FS = ^VREF
2
ZS = 0
-FS = ^-VREF
2
1 LSB = ^VREF
4096
100....001
100....000
-FS
0
+FS - 1 LSB
INPUT VOLTAGE (LSB)
OUTPUT CODE
011....111
011....110
000....010
000....001
000....000
111....111
111....110
111....101
100....001
100....000
-256°C
0
TEMPERATURE °C
+255.875°C
Figure 11. Bipolar Transfer Function, Full Scale (±FS) = ±V_REF/2
Figure 12. Temperature Transfer Function
Transfer Function
Figure 10 shows the nominal transfer function for single-
ended or differential unipolar configured inputs, Figure
11 illustrates the transfer function for differential bipolar
conversions, and Figure 12 shows temperature conver-
sions. Code transitions occur halfway between succes-
sive-integer LSB values. Output coding is binary, with
1 LSB = 610µV (MAX1253) or 1mV (MAX1254) for unipo-
lar and bipolar operation, and 1 LSB = +0.125°C
(MAX1253/MAX1254) for temperature measurements.
For unipolar operation, the 0 code level transition is at
[1/2(V_REF / 4096)].
The FFF hex level transition is at [4094.5 (V_REF / 4096)].
1 LSB = V_REF / 4096.
Layout, Grounding, and Bypassing
For best performance, use PC boards. Do not use wire-
wrap boards. Board layout should ensure that digital
and analog signal lines are separated from each other.
Do not run analog and digital (especially clock) signals
parallel to one another or run digital lines underneath
the MAX1253/MAX1254 package. High-frequency
noise in the V_DD power supply can affect the
MAX1253/MAX1254 performance. Bypass the V_DD sup-
ply with a 0.1µF capacitor from V_DD to GND, close to
the V_DD pin. Minimize capacitor lead lengths for best
supply-noise rejection. If the power supply is very
noisy, connect a 10Ω resistor in series with the supply
to improve power-supply filtering.
Definitions
Integral Nonlinearity
Integral nonlinearity is the deviation of the values on the
actual transfer function from a straight line. This straight
line can be either a best-straight-line fit or a line drawn
between the end points of the transfer function, once off-
set and gain errors have been corrected. The static lineari-
ty parameters for the MAX1253/MAX1254 are measured
using the end-point-fit method. INL is specified as the
maximum deviation in LSBs.
Differential Nonlinearity (DNL)
Differential nonlinearity is the difference between an
actual step width and the ideal value of 1 LSB. A DNL
error specification of less than 1 LSB guarantees no
missing codes and a monotonic transfer function.
Offset Error
The offset error is the difference between the ideal and
the actual analog input value at the first transition of the
ADC, usually from digital code 0 to code 1 for straight
binary output. For the MAX1253/MAX1254, the transi-
tion between code 0 and code 1 should occur at an
input voltage of 1/2 LSB, or 305µV for the MAX1253
and 500µV for the MAX1254.
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