The CO transimpedance amplifier is a low-offset, low-power op-amp with integrated input, gain, and output resistors. Each of these resistors can be disconnected using the COSW register bits if using external resistors. The input resistor limits amplifier current during a CO sensor connectivity test. The gain resistor amplifies the CO sensor signal. Adjust the gain resistor by changing the COGAIN register bits. Use the output resistor with an external capacitor to filter the CO amplifier output signal.

The CO amplifier has two integrated references. A programmable 1.25-mV to 5-mV reference COREF is internally connected to the op-amp positive terminal. A 300-mV reference is connected to the REF0P3 pin. When the millivolt reference is used, the CO sensor must be connected to GND. The millivolt reference is amplified to offset the amplifier output above GND. When the 300 mV reference is used, the reference offsets the CO amplifier output by 300 mV. In general, either reference can be used. The 300-mV reference offers better DC accuracy at the cost of extra power consumption. The 300 mV reference is generated with a reference and op-amp buffer for high precision. The REF0P3 pin must connect to a 1 nF capacitor for stability if it is enabled. The buffer is designed to source and sink small currents as required by the CO amplifier. The 300 mV reference and the 1.25 mV to 5mV reference cannot be enabled simultaneously.

A resistor connected in parallel with the CO sensor prevents charge from accumulating across its terminals. The output of the CO amplifier is connected to the COO pin for continuous monitoring and the AMUX for periodic sampling.