Microchip TC9401CPD Precision Converter

The Microchip TC9401CPD is a monolithic CMOS frequency-to-voltage (F/V) and voltage-to-frequency (V/F) converter designed for precision measurement and signal conditioning applications. Housed in a 14-pin DIP (Dual In-line Package), this IC provides a full-scale frequency of 100 kHz with excellent linearity of 0.01% typical. It is suitable for instrumentation, analog data acquisition, frequency demodulation, and isolated signal transmission systems.

Technical Specifications

The TC9401 operates with a single supply voltage from +8V to +15V or dual supplies ±4V to ±7.5V. Quiescent current is typically 1.2 mA. Input voltage range for V/F conversion is 0 to +10V. Output frequency range is 0 to 100 kHz full scale. Gain drift is ±50 ppm/°C typical, and offset drift is ±10 µV/°C. Linearity error is 0.01% for 10 kHz full scale and 0.05% for 100 kHz full scale. The converter consumes 30 mW typical at 15V supply.

Key performance parameters: Charge balance architecture provides monotonic operation over entire temperature range. Input impedance is 10 MΩ typical. Output for F/V mode is a buffered voltage proportional to input frequency. The device includes an internal 2.5V reference (drift ±50 ppm/°C) and an operational amplifier for output signal conditioning. Operating temperature range is 0°C to +70°C (CPD suffix).

Key Features

• Dual mode: frequency-to-voltage or voltage-to-frequency

• Full scale frequency up to 100 kHz

• Linearity error: 0.01% (typ.) at 10 kHz FS, 0.05% at 100 kHz FS

• Wide supply range: +8V to +15V single or ±4V to ±7.5V dual

• Low quiescent current: 1.2 mA typical

• Internal precision voltage reference

• High input impedance (10 MΩ)

• Low drift: gain ±50 ppm/°C, offset ±10 µV/°C

• 14-pin PDIP package (through-hole)

• RoHS compliant

Functional Description

The TC9401 uses a charge-balance architecture. In V/F mode, the input voltage is converted to a pulse train with frequency linearly proportional to the analog input. The output is an open-collector transistor that requires a pull-up resistor (typically 2.2kΩ to 5V). In F/V mode, an external frequency is applied to the input, and the IC outputs a voltage proportional to that frequency. The conversion formula is Vout = Fin × (Vref × Rset × Cint). External resistor and capacitor values determine the scaling. Typical component values: Rset = 100kΩ, Cint = 0.01µF for 100 kHz full scale.

Applications

The TC9401CPD is widely used for:

• Frequency-to-voltage conversion for tachometers, flow meters, and speed sensors

• Voltage-to-frequency conversion for isolated analog signal transmission (e.g., optocoupler or transformer isolation)

• Analog data acquisition systems requiring noise immunity

• FM demodulation for communication systems

• Digital voltmeters and panel meters

• Low-cost analog-to-digital conversion (counting output pulses)

Pin Configuration and Circuit Design

The 14-pin DIP package provides separate inputs for V/F and F/V modes, reference voltage access, and output buffer connections. Pin 1 is output frequency, pin 2 and 3 for timing components, pin 4 ground, pin 5 input voltage, pin 6 reference, pins 7 and 8 for op-amp connections, pin 9 F/V input, pin 10 and 11 for F/V timing, pin 12 output voltage, pin 13 V+, pin 14 V-. Application circuits in the datasheet show typical connections for both modes with calibration procedures for offset and gain trimming. For optimal linearity, use precision metal-film resistors and NPO/C0G capacitors.

Absolute Maximum Ratings

Supply voltage: +18V (single) or ±9V (dual). Input voltage range: -0.3V to (V+ + 0.3V). Storage temperature: -65°C to +150°C. Lead temperature (soldering, 10 seconds): 300°C. Exceeding these ratings may cause permanent damage. Proper decoupling with 0.1µF ceramic capacitor close to supply pins is recommended.

Conclusion

The Microchip TC9401CPD offers a versatile, low-cost solution for precision frequency-to-voltage or voltage-to-frequency conversion. Its excellent linearity, wide frequency range, and simple external component requirements make it ideal for industrial and instrumentation applications. The 14-pin DIP package facilitates prototyping and through-hole PCB assembly.