MAX1478 Datasheet, PDF (4/20 Pages) Maxim Integrated Products – 1% Accurate, Digitally Trimmed,Rail-to-Rail Sensor Signal Conditioner

1% Accurate, Digitally Trimmed,
Rail-to-Rail Sensor Signal Conditioner
Pin Description
PIN
1
2
3, 11,
16
4
5
6
7
8
9
10
12
13
14
15
NAME
SCLK
CS
I.C.
TEMP
FSOTC
DIO
WE
V_SS
ISRC
OUT
INP
BDRIVE
INM
V_DD
FUNCTION
Data Clock Input. Used only during programming/testing. Internally pulled to V_SS with a 1MΩ (typical) resis-
tor. Data is clocked in on the rising edge of the clock. The maximum SCLK frequency is 10kHz.
Chip-Select Input. The MAX1478 is selected when this pin is high. When low, OUT and DIO become high
impedance. Internally pulled to V_DD with a 1MΩ (typical) resistor. Leave unconnected for normal operation.
Internally Connected. Leave unconnected.
Temperature Sensor Output. An internal temperature sensor (a 100kΩ, 4600ppm/°C TC resistor) that can
provide a temperature-dependent voltage.
Buffered FSOTC DAC Output. An internal 75kΩ resistor (R_FTC) connects FSOTC to ISRC (see Functional
Diagram). Optionally, external resistors can be used in place of or in parallel with R_FTC and R_ISRC.
Data Input/Output. Used only during programming/testing. Internally pulled to V_SS with a 1MΩ (typical)
resistor. High impedance when CS is low.
Dual-Function Input Pin. Used to enable EEPROM erase/write operations. Also used to set the DAC refresh-
rate mode. Internally pulled to V_DD with a 1MΩ (typical) resistor. See the Chip-Select (CS) and Write-Enable
(WE) section.
Negative Power-Supply Input
Current-Source Reference. An internal 75kΩ resistor (R_ISRC) connects ISRC to V_SS (see Functional
Diagram). Optionally, external resistors can be used in place of or in parallel with R_FTC and R_ISRC.
PGA Output Voltage
Positive Sensor Input. Input impedance >1MΩ. Rail-to-rail input range.
Sensor Excitation Current Output. This current source drives the bridge.
Negative Sensor Input. Input impedance >1MΩ. Rail-to-rail input range.
Positive Power-Supply Input. Connect a 0.1µF capacitor from V_DD to V_SS.
_______________Detailed Description
The MAX1478 provides an analog amplification path for
the sensor signal. Calibration and temperature com-
pensation are achieved by varying the offset and gain
of a programmable-gain amplifier (PGA) and by varying
the sensor bridge current. The PGA uses a switched-
capacitor CMOS technology, with an input-referred
coarse offset trimming range of approximately ±63mV
(9mV steps). An additional output-referred fine offset
trim is provided by the Offset DAC (approximately
2.8mV steps). The PGA provides eight gain values from
+41V/V to +230V/V. The bridge current source is pro-
grammable from 0.1mA to 2mA.
The MAX1478 uses four 12-bit DACs and one 3-bit
DAC, with calibration coefficients stored by the user in
an internal 128-bit EEPROM. This memory contains the
following information as 12-bit-wide words:
• Configuration register
• Offset calibration coefficient
• Offset temperature error-compensation coefficient
• FSO (full-span output) calibration coefficient
• FSO temperature error-compensation coefficient
• 24 user-defined bits for customer programming of
manufacturing data (e.g., serial number and date)
Figure 1 shows a typical pressure-sensor output and
defines the offset, full-scale, and FSO values as a func-
tion of voltage.
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