Mastering Power Supply Design with the Microchip TC7660EOA713 CMOS Voltage Converter

The Microchip TC7660EOA713 stands as a quintessential component in the realm of power management, offering designers a simple, efficient, and cost-effective solution for voltage conversion. This CMOS-based charge pump voltage converter is engineered to invert a positive input voltage in the range of +1.5V to +12V to a corresponding negative output voltage (-1.5V to -12V). It can also be configured to double an input voltage. Its inherent simplicity and low external part count make it an ideal choice for applications requiring a moderate current, negative supply rail.

Key Features and Electrical Characteristics

The TC7660EOA713 excels due to its core attributes. It operates with a high power conversion efficiency, typically exceeding 99%, thanks to its CMOS construction which minimizes quiescent power consumption. The device requires a minimal number of external components—typically just two flying capacitors and two reservoir capacitors—to form a complete voltage inverter circuit. It features a wide operating voltage range and can deliver output currents up to 20mA, with a output impedance of approximately 50Ω at room temperature. Furthermore, it includes an internal oscillator that typically runs at 10kHz, though an external clock can be used to drive it for specialized applications requiring a different frequency.

Application Circuit Design: A Standard Voltage Inverter

The most fundamental application of the TC7660EOA713 is the voltage inverter circuit. The design is remarkably straightforward:

1. Input Decoupling: A bypass capacitor (typically 10µF) is placed directly across the V+ and GND pins near the IC to suppress source impedance and noise.

2. Charge Pump Capacitors: Two identical capacitors are critical. The flying capacitor (C1), connected between pins 2 (CAP+) and 4 (CAP-), is responsible for transferring charge. Its value directly impacts the output impedance; a value of 10µF is standard for most applications.

3. Output Filtering: The output reservoir capacitor (C2), connected from VOUT to GND, smoothes the switched output to a stable DC voltage. A value equal to or larger than the flying capacitor (e.g., 10µF) is recommended.

For optimal performance, especially at higher currents or lower temperatures, a Schottky diode should be connected in series with the output. This diode prevents the device from latching up under certain conditions by blocking current flow back into the IC.

Expanding Functionality: Voltage Doubling and Regulation

Beyond inversion, the TC7660 can be configured as a voltage doubler. This is achieved by connecting pin 5 (LV) to GND, grounding pin 4 (CAP-), and driving the pump from pin 2 (CAP+). The input voltage is applied between V+ and GND, and the output, which is approximately twice the input voltage, is taken from V+ relative to pin 2.

While the TC7660 is an unregulated converter, its output voltage will droop as the load current increases due to its inherent output impedance. For applications requiring a highly stable voltage, a low-dropout linear regulator (LDO) can be placed at the output of the TC7660. This combination provides a clean, regulated negative voltage rail from a positive source.

ICGOODFIND Summary

The Microchip TC7660EOA713 is a highly versatile and fundamental building block for power supply design. Its primary strength lies in its exceptional simplicity, requiring only a handful of passive components to generate a negative voltage from a positive source. Designers value it for its high efficiency, low power consumption, and flexibility in applications ranging from op-amp power supplies and data acquisition systems to LCD bias generators. When a design calls for a simple, low-current, inverting or doubling power solution, the TC7660 remains a top contender and a testament to elegant, effective engineering.

Keywords:

CMOS Voltage Converter

Charge Pump

Negative Voltage Generator

Application Circuit

Power Conversion Efficiency