Charge Pump Voltage Converters: A Deep Dive into the Microchip TC7662BCOA
In the realm of electronic design, efficiently generating a required voltage rail from an existing supply is a fundamental challenge. While inductor-based switching regulators are powerful, they introduce complexity, cost, and potential EMI. For many applications, a simpler, cost-effective, and EMI-quiet solution is preferable. This is where the charge pump voltage converter excels, and the Microchip TC7662BCOA stands as a quintessential example of this robust and versatile technology.
What is a Charge Pump?
A charge pump is a type of DC-DC converter that uses capacitors, rather than inductors, to store and transfer energy. Its operation is elegantly simple: it works by first charging a "flying" capacitor to the input voltage and then reconfiguring the circuit to connect this capacitor in series with the input supply or ground, effectively doubling or inverting the input voltage. This switching action, controlled by an internal oscillator, happens thousands of times per second, providing a regulated output.
Introducing the Microchip TC7662BCOA
The TC7662BCOA is a monolithic, CMOS voltage converter IC designed to generate a negative output voltage from a positive input. Housed in a space-saving 8-pin SOIC package, it can also perform voltage doubling. Its key specifications include:
Wide Input Voltage Range: +1.5V to +12V, making it compatible with 3.3V, 5V, and 12V systems.
Output Current: Up to 20mA, suitable for powering op-amps, sensors, and other low-power circuitry.
High Voltage Conversion Efficiency: Typically >99%, as it primarily incurs losses from internal switch resistance.
Low Power Consumption: Typically 80µA, ideal for battery-powered devices.
Pin-for-Pin Compatible: A second-source replacement for the industry-standard ICL7662.
Key Features and Operational Modes
The strength of the TC7662BCOA lies in its flexibility and integrated features:
1. Voltage Inversion: This is its primary function. By connecting the V+ pin to a positive supply (e.g., +5V), the CAP- and CAP+ pins to an external capacitor, and using another capacitor to buffer the output, the device provides a regulated -5V output at the VOUT pin.
2. Voltage Doubling: By reconfiguring the external components, the same IC can double an input voltage. For example, a +5V input can be converted to +10V, showcasing its exceptional versatility.
3. Oscillator Control: The device features an internal oscillator (~10kHz) but also provides an OSC pin. This allows an external clock to be used for synchronization or to drive the device at a higher frequency, which reduces the required size of the external capacitors.
4. LV Pin (Low Voltage): For operation below 3.5V, tying the LV pin to V+ ensures proper functionality and improved efficiency in low-voltage scenarios, a critical feature for modern, low-power electronics.
Advantages and Practical Considerations
The TC7662BCOA offers distinct benefits:
Simplicity: Requires only two external capacitors—no inductors, no complex magnetics.
Low Cost: A highly economical solution for generating a secondary voltage.
Minimal Noise: The absence of an inductor eliminates magnetic radiated EMI, a significant advantage in noise-sensitive analog and RF circuits.
Small Footprint: The entire solution fits into a very small PCB area.
Designers must consider its limitations, primarily the limited output current. The output impedance is relatively high (typically ~50Ω), meaning the output voltage will droop as the load current increases. Careful selection of the flying and output capacitor values (typically 10µF) is crucial for optimal performance.
The Microchip TC7662BCOA is an ICGOODFIND for any engineer needing a simple, reliable, and cost-effective method for generating a negative or doubled voltage. Its inductorless design, low power consumption, and robust feature set make it an enduring and excellent choice for a vast array of applications, from portable instruments and audio equipment to industrial sensor interfaces. It perfectly embodies the principle that the most elegant solutions are often the simplest.
Keywords:
Charge Pump
Voltage Converter
DC-DC Converter
Microchip TC7662BCOA
Voltage Inversion
