Modern day microcontrollers are equipped with one or more dedicated PWM peripherals built-in that can be used to generate analog output voltages with varying range by just using a basic RC filter circuit. While this is a very simple and practical approach, it has some limitations such as it can only drive high impedance load and the processor should continuously output the PWM signal to maintain the output voltage constant, which prohibits the processor to be put into a low power shutdown state when required. This application note from Linear Technology describes the use of LTC644 and LTC2645 chips, which are dual and quad PWM-to-voltage output DACs, to overcome these problems by directly measuring the duty cycle of the incoming PWM signal and sending the appropriate 8-, 10- or 12-bit code to a precision DAC at each rising edge.
Improving PWM-to-Analog conversion
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