MAX1458 Datasheet, PDF (7/20 Pages) Maxim Integrated Products – 1%-Accurate, Digitally Trimmed Sensor Signal Conditioner

1%-Accurate, Digitally Trimmed
Sensor Signal Conditioner
V_DD
FSO
DAC
I_SRC
V_DD
I = I_ISRC AA ≈ 14I_ISRC = I_BDRIVE
BDRIVE
FSOTC
DAC
R_FTC
R_ISRC
EXTERNAL
SENSOR
FSOTC
Figure 3. Bridge Excitation Circuit
a V_DD of 5V. The output of the Offset DAC is fed into
the output summing junction where it is gained by
approximately 2.3, which increases the resulting out-
put-referred offset correction resolution to 2.8mV.
Both the Offset TC and FSOTC DACs take their refer-
ence from BDRIVE, a temperature-dependent voltage. A
nominal V_BDRIVE of 2.5V results in a step size of 0.6mV.
The Offset TC DAC output is fed into the output sum-
ming junction where it is gained by approximately 2.3,
thereby increasing the Offset TC correction range. The
buffered FSOTC DAC output is available at FSOTC and
is connected to ISRC via R_FTC to correct FSOTC errors.
Internal Resistors
The MAX1458 contains three internal resistors (R_ISRC,
R_FTC, and R_TEMP) optimized for common silicon PRTs.
R_ISRC (in conjunction with the FSO DAC) programs the
nominal sensor excitation current. R_FTC (in conjunction
with the FSOTC DAC) compensates the FSOTC errors.
Both R_ISRC and R_FTC have a nominal value of 75kΩ. If
external resistors are used, R_ISRC and R_FTC can be dis-
abled by resetting the appropriate bit (address 07h
reset to zero) in the configuration register (Table 3).
R_TEMP is a high-tempco resistor with a TC of
+4600ppm/°C and a nominal resistance of 100kΩ at
+25°C. This resistor can be used with certain sensor
types that require an external temperature sensor.
Table 3. Configuration Register
EEPROM
ADDRESS (hex)
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
0Bh
DESCRIPTION
Offset TC Sign Bit, SOTC
Offset Sign Bit, SOFF
PGA Gain (MSB), A2
PGA Gain, A1
PGA Gain (LSB), A0
Reserved “0”
Reserved “0”
Internal Resistor (R_FTC and R_ISRC)
Selection
Input-Referred Offset (IRO) Sign Bit
Input-Referred Offset (MSB)
Input-Referred Offset
Input-Referred Offset (LSB)
Internal EEPROM
The MAX1458 has a 128-bit internal EEPROM arranged
as eight 16-bit words. The four uppermost bits for each
register are reserved. The internal EEPROM is used to
store the following (also shown in the memory map in
Table 4):
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