The AD650 is a versatile monolithic voltage-to-frequency converter (VFC) that utilizes a charge-balanced architecture to obtain high performance in many applications. This application note discusses the F/V architecture and operation, component selection, a design example, and the fundamental trade-off between output ripple and circuit response time.
This application note explains the architecture and operation of using the AD650 monolithic voltage-to-frequency converter in reverse mode as a frequency-to-voltage (F/V) converter. It details the circuit components, including a comparator, one-shot, constant current source, and lossy integrator, and provides the theoretical basis for the conversion process.
The document provides a step-by-step design procedure for selecting component values such as the one-shot time constant, integration resistor, and integration capacitor. It includes a specific design example for monitoring an automobile engine's RPM and discusses the trade-off between output ripple and circuit response time.
The current source value for the AD650 is 1 mA.
An RC network needs six time constants to settle to eight bits of accuracy.
The calculated ripple is 6.25 mV at 300 rpm.