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MAX40109

Precision Signal Conditioning AFE for Pressure

Sensor Applications

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Use External Resistor for Bridge Current Source

The MAX40109 can drive the sensor bridge with either voltage or current.

When driving with current, the current source is integrated into the device. The temperature coefficient of the current

source is dominated by the temperature drift of the internal resistor, which is 50ppm/°C (typ).

The user may use an external resistor with a lower temperature coefficient, as shown in the following diagram. The

external sense resistor (REXT) is connected to the input pin INT. Its nominal value should be 100kΩ. The internal

resistor (RINT) is 50kΩ nominally. In this case, it will not be possible to connect a thermistor to INT. However, the

temperature measurement from the bridge resistor (through DRV) is still allowed.

DRV

MAX40109

INT

RINT

REXT

CURRENT

MIRROR

EXTERNAL

CURRENT SET

RESISTOR

VREF

BRIDGE

SENSOR

Figure 24. External Resistor for Current Bridge Source

Ratio-metric Voltage Output

To create a 0-5V voltage output that is ratio-metric with the supply voltage, the following step is required:

• Program the MTP memory register Analog Output Stage to select option 0x1.

It is possible to drop VDDHV to a level below the internal LDO output voltage of VDD5V. In this case, the internal LDO is

in drop-out mode. See the Electrical Characteristics table for the drop-out voltage.

Sensor Offset Calibration

This section describes the procedure required to calibrate the sensor offset.

• User activates “pressure_cal_bypass” (configuration register, bit 13) to enter bridge offset calibration mode. Start at

room temp.

• Bypass the pressure PGA gain (see register Sensor Offset Cal Config).

• User measures offset with a default setting of gain = 2V/V.

• If preferred, for more accuracy, the user can adjust gain such that the signal at the input of the ADC is within ½ ADC

full-scale and ADC full-scale.

• User determines the correct offset calibration code based on the table below (to be added).

• Highly recommended: If the user wants to check offset calibration code accuracy without writing to MTP, they can load

trim code into a register “ZERO_PRESSURE_OFFSET<15:0>” and reconnect the internal trim resistor and the offset

calibration current source to measure the residue (set bits 2 and 1 of Sensor Offset Cal Config).

• Adjust trim code to achieve acceptable residue. It is highly recommended to confirm residue with the final trim code.

• User deactivates “pressure_cal_bypass”

• Write trim code into MTP.

MAX40109 Datasheet(PDF) 52 Page - Analog Devices

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