Charge Pump Voltage Conversion with the Microchip TC7660COA713

Voltage inversion and doubling are fundamental requirements in many electronic systems, particularly where a negative supply rail is needed for operational amplifiers, sensors, or interface circuits but only a single positive source is available. While switched-mode power supplies (SMPS) offer high efficiency, their complexity, cost, and potential for noise can be prohibitive for simpler applications. A more straightforward and cost-effective solution is the charge pump voltage converter, exemplified by the Microchip TC7660COA713.

The TC7660COA713 is a monolithic, CMOS-based voltage converter IC designed to generate an output voltage that is the inverse of its input. Its primary function is to efficiently convert a positive input voltage in the range of +1.5V to +12V to a corresponding negative output (e.g., +5V in becomes –5V out). It can also be configured as a voltage doubler. Housed in a robust 8-pin SOIC package, this device is ideal for space-constrained PCB designs.

The core principle behind its operation is a switched-capacitor technique. The internal oscillator controls a set of four MOSFET switches that form a double-pole, double-throw (DPDT) switch. This network alternately connects an external flying capacitor (`C1`) between the input voltage for charging and the output reservoir capacitor (`C2`) for discharging in the inverted polarity. This "pumping" action efficiently transfers charge from the input to the output, creating the negative supply. The device features a typical power conversion efficiency of 99% and a voltage conversion efficiency of 99.9%, making it highly effective for low-to-medium current applications.

Key advantages of the TC7660COA713 include its exceptional simplicity and low external component count. Only two inexpensive, non-critical capacitors—the flying capacitor (`C1`) and the output reservoir capacitor (`C2`)—are required for basic operation, dramatically reducing the bill of materials and board space compared to an inductive SMPS. Furthermore, it eliminates the magnetic fields and associated electromagnetic interference (EMI) typical of inductor-based regulators, making it a cleaner solution for noise-sensitive analog and RF circuits.

The internal oscillator typically runs at 10 kHz, but the device includes an optional oscillator frequency boost pin (`OSC`). Leaving this pin open sets the standard frequency, while connecting it to ground increases the frequency, allowing the use of smaller capacitor values. Connecting it to `V+` disables the internal oscillator, permitting synchronization to an external clock source for precise noise control.

Typical applications are vast, including generating negative bias for op-amps, powering RS-232 interface ICs from a single +5V supply, and providing a simple voltage doubler to create a higher positive rail. Its low power consumption also makes it suitable for battery-operated portable equipment.

ICGOOODFIND: The Microchip TC7660COA713 stands out as an elegant, robust, and highly practical solution for on-board voltage inversion and doubling. Its unparalleled simplicity, minimal external part requirement, and lack of inductors make it an indispensable component for designers seeking to add a secondary supply rail without introducing complexity or noise.

Keywords: Charge Pump, Voltage Inverter, Switched Capacitor, Negative Voltage Generator, TC7660.