A Comprehensive Guide to the Microchip TC7660COA Voltage Converter
In the world of electronics, generating a negative voltage from a single positive supply is a common and crucial requirement for powering various components like operational amplifiers, sensors, and interface circuits. The Microchip TC7660COA stands as a robust, industry-standard solution for this very purpose. This integrated circuit is a monolithic, CMOS-based voltage converter that efficiently performs voltage doubling and inverting, making it an indispensable component in countless designs.
Understanding the Core Functionality
At its heart, the TC7660COA is a switched-capacitor voltage converter. It does not rely on magnetic components like inductors, which can be bulky and introduce EMI. Instead, it uses an external capacitor to "pump" and transfer charge, creating an inverted output voltage.
The principle is elegantly simple: in the first phase of its internal oscillator's cycle, the flying capacitor is charged to the input voltage (V+). In the second phase, the capacitor is switched so that it is effectively in series with the input voltage and the ground. This action precisely inverts the polarity of the voltage across the capacitor, resulting in a negative output voltage with a magnitude approximately equal to the positive input voltage, i.e., Vout ≈ -Vin.
Key Features and Specifications
The TC7660COA is prized for its simplicity and performance. Its notable characteristics include:
Wide Input Voltage Range: It can operate from a supply voltage between 1.5V to 12V, making it versatile for both low-voltage modern microcontrollers and higher voltage systems.
High Voltage Conversion Efficiency: Typically greater than 99%, ensuring minimal energy is lost in the conversion process.
Low Power Consumption: As a CMOS device, it draws very little quiescent current (typically 50µA), which is critical for battery-powered applications.
Pin-Compatible Upgrade: It is a direct and improved replacement for the classic ICL7660, offering better performance over a wider voltage range.
Simple External Components: Requires only two inexpensive, external capacitors for operation—one for charge pumping and one for output filtering.
Available in 8-Pin SOIC Package: The "COA" suffix denotes the Chiplate™ (SOIC) package, which is easy to prototype with and suitable for automated assembly.
Application Circuits
The most common application is the voltage inverter. By connecting the flying capacitor between pins 2 (CAP+) and 4 (CAP-) and using a reservoir capacitor at the output (pin 5), the device generates -Vin from +Vin.
Furthermore, by slightly modifying the circuit configuration, the TC7660 can also function as a voltage doubler, generating an output of approximately 2 × Vin. It can even be used as a voltage multiplier by cascading multiple devices for higher output voltages.
Design Considerations and Best Practices
To ensure optimal performance, several factors must be considered:
Capacitor Selection: Low-ESR ceramic capacitors are highly recommended. Values between 10µF and 100µF are typical, with larger values helping to reduce output ripple, especially under higher load currents.
Output Impedance: The output resistance is a function of the oscillator frequency and the flying capacitor value. Higher load currents will cause a greater voltage drop from the ideal -Vin value.
Oscillator Frequency: The device has an internal oscillator (~10kHz), but an external clock can be applied to pin 1 (OSC) to drive it at a higher frequency. This allows for the use of smaller capacitor values but may slightly reduce conversion efficiency.
LV Pin: Pin 7 (LV) must be connected to ground for supply voltages below 3.5V to ensure proper operation. For voltages above 3.5V, it can be left floating.
The Microchip TC7660COA is a quintessential example of a simple, effective, and reliable integrated circuit that solves a fundamental design challenge. Its inductorless design, low cost, and ease of use have cemented its status as a go-to component for engineers needing efficient voltage conversion without the complexity of switching regulators. It remains a perfect solution for generating local negative supplies in a wide array of analog and mixed-signal circuits.
Keywords: Voltage Converter, Switched Capacitor, TC7660, Negative Voltage Generator, CMOS
