How to Use LMP91000: Examples, Pinouts, and Specs

The LMP91000 is a low-power, high-performance potentiostat designed by Texas Instruments for use in electrochemical sensor applications. It integrates a programmable gain amplifier (PGA), a reference voltage output, and configurable bias settings, making it highly versatile for interfacing with a wide range of electrochemical sensors, such as gas sensors, pH sensors, and amperometric sensors.

• Environmental monitoring (e.g., gas detection, air quality sensors)
• Medical diagnostics (e.g., blood glucose monitoring, lactate sensors)
• Industrial process control (e.g., chemical analysis, corrosion monitoring)
• Research and development in electrochemical sensing

The LMP91000 is particularly valued for its low power consumption, making it suitable for portable and battery-powered devices.

The LMP91000 is available in a 14-pin WSON package. Below is the pinout and description:

1. Power Supply: Connect the VDD pin to a regulated power supply (2.7V to 5.25V) and GND to the ground.
2. Sensor Connections:
   • Connect the CE, RE, and WE pins to the counter, reference, and working electrodes of the electrochemical sensor, respectively.
3. Reference Voltage: Use the VREF pin to provide a stable reference voltage to the sensor. This voltage can be programmed via the I²C interface.
4. External Capacitors: Connect capacitors to the C1 and C2 pins as specified in the datasheet for proper filtering.
5. I²C Communication: Use the SDA and SCL pins to communicate with the LMP91000 via an I²C master device (e.g., a microcontroller or Arduino).

• Sensor Bias Configuration: Configure the sensor bias voltage and gain settings via the I²C interface to match the requirements of your specific sensor.
• Power Consumption: The LMP91000 is optimized for low power consumption, but ensure proper power management in battery-powered applications.
• PCB Layout: Minimize noise by placing decoupling capacitors close to the VDD and GND pins. Keep traces to the sensor electrodes as short as possible.
• Startup Sequence: Ensure the power supply is stable before initializing the I²C communication.

Below is an example of how to interface the LMP91000 with an Arduino UNO using I²C communication:

#include <Wire.h> // Include the Wire library for I²C communication

#define LMP91000_I2C_ADDR 0x48 // Default I²C address of the LMP91000

void setup() {
  Wire.begin(); // Initialize I²C communication
  Serial.begin(9600); // Initialize serial communication for debugging

  // Configure the LMP91000
  Wire.beginTransmission(LMP91000_I2C_ADDR);
  Wire.write(0x10); // Write to the TIACN register (Transimpedance amplifier control)
  Wire.write(0x03); // Set gain to 7kΩ and RLOAD to 10Ω
  Wire.endTransmission();

  Serial.println("LMP91000 configured successfully.");
}

void loop() {
  // Example: Read a register from the LMP91000
  Wire.beginTransmission(LMP91000_I2C_ADDR);
  Wire.write(0x00); // Point to the STATUS register
  Wire.endTransmission();

  Wire.requestFrom(LMP91000_I2C_ADDR, 1); // Request 1 byte from the STATUS register
  if (Wire.available()) {
    byte status = Wire.read();
    Serial.print("STATUS Register: 0x");
    Serial.println(status, HEX);
  }

  delay(1000); // Wait for 1 second before the next read
}

1. No Output from the Sensor:

   • Ensure the sensor is properly connected to the CE, RE, and WE pins.
   • Verify that the sensor bias voltage and gain settings are correctly configured via I²C.

2. I²C Communication Fails:

   • Check the connections to the SDA and SCL pins.
   • Ensure pull-up resistors (typically 4.7kΩ) are connected to the SDA and SCL lines.
   • Verify the I²C address of the LMP91000 (default is 0x48).

3. High Noise in Output:

   • Ensure proper decoupling capacitors are placed near the VDD and GND pins.
   • Minimize the length of traces connecting the sensor electrodes to the LMP91000.

4. Incorrect Reference Voltage:

   • Verify the VREF configuration via I²C.
   • Ensure the power supply voltage (VDD) is stable and within the specified range.

Q: Can the LMP91000 be used with a 3.3V microcontroller?
A: Yes, the LMP91000 operates with a supply voltage as low as 2.7V, making it compatible with 3.3V systems.

Q: What types of sensors are compatible with the LMP91000?
A: The LMP91000 supports a wide range of electrochemical sensors, including amperometric, potentiometric, and voltammetric sensors.

Q: How do I change the I²C address of the LMP91000?
A: The I²C address can be modified by configuring the ADDR pin. Refer to the datasheet for specific address selection options.

This documentation provides a comprehensive guide to understanding, using, and troubleshooting the LMP91000 potentiostat. For further details, refer to the official Texas Instruments datasheet.