Charge Pump Voltage Converter with the Microchip TC7662AEPA
Voltage conversion is a fundamental requirement in modern electronic design, where components often require different supply levels than what is available from a primary source like a battery or a fixed rail. While inductor-based switching regulators are common for high-power applications, they introduce complexity, cost, and potential EMI issues. For many low-to-medium power applications, a simpler, more elegant solution exists: the charge pump voltage inverter. The Microchip TC7662AEPA is a quintessential example of this type of IC, offering a robust and highly efficient method for generating a negative voltage from a positive input.
Operating Principle of a Charge Pump
At its core, a charge pump is a type of DC-DC converter that uses capacitors as energy storage elements to create a higher or inverted voltage. The TC7662AEPA primarily functions as a voltage inverter, producing `-VIN` from `+VIN`. Its operation is elegantly simple, relying on a two-phase switching cycle controlled by an internal oscillator.
In the first phase, an internal switch network connects an external "flying" capacitor (`C1`) between the input voltage (`V+`) and ground, allowing it to charge to approximately `V+`. In the second phase, the switch network reconfigures, disconnecting the capacitor from ground and instead connecting it between the output capacitor (`C2`) and the system ground. This effectively places the charged capacitor in series with the input voltage. Since the positive side of `C1` is now connected to ground, its negative side provides a voltage of approximately `-V+` to the output capacitor, which smooths this pulsed voltage into a stable negative rail.
Key Features and Advantages of the TC7662AEPA
The TC7662AEPA stands out due to its exceptional simplicity and performance. Housed in an 8-pin PDIP package, it requires only two external capacitors—one flying capacitor and one output capacitor—to form a complete voltage inverter circuit. This minimal component count translates to a highly compact and cost-effective PCB footprint.
A significant advantage of this architecture is its high power conversion efficiency, typically exceeding 99%. This is because the energy transfer is primarily handled by capacitors and low-resistance MOSFET switches, minimizing resistive power losses common in inductor-based systems. Furthermore, as a switched capacitor converter, it operates without an inductor, making it inherently immune to magnetic field radiation and thus an excellent choice for noise-sensitive applications.
The device operates over a wide input voltage range from 1.5V to 12V, making it versatile for everything from single-cell battery applications to standard 12V systems. Its built-in oscillator typically runs at 10 kHz, but an optional OSC pin allows for frequency control, either by adding an external capacitor to slow it down or by synchronizing it to an external clock to avoid interference with sensitive circuits.
Typical Application Circuit
Implementing the TC7662AEPA is straightforward. The basic inverter configuration requires:
Pin 8 (V+): Connected to the positive supply voltage (e.g., +5V).
Pin 3 (GND): Connected to system ground.
Pin 2 (CAP+): Connected to one terminal of the flying capacitor (`C1`).
Pin 4 (CAP-): Connected to the other terminal of `C1`. A 10µF ceramic or tantalum capacitor is typical.
Pin 5 (OUT): Provides the negative output voltage (e.g., -5V). This pin is connected to ground through the output capacitor (`C2`), also typically 10µF.
Pin 1 (LV): For supplies below 3.5V, this pin must be tied to GND to reduce internal switch resistance and improve efficiency. For higher voltages, it can be left floating.
Conclusion and Design Considerations
The Microchip TC7662AEPA is an indispensable tool for designers who need to generate a low-noise, low-current negative supply rail without the complexity of magnetic components. Its robust performance and extreme simplicity make it ideal for powering op-amp circuits, sensors, LCD biases, and other sub-systems requiring a dual-rail supply from a single battery or wall adapter. When designing, careful PCB layout is recommended, with the flying and output capacitors placed as close as possible to the IC to minimize parasitic inductance and ensure optimal performance.
ICGOODFIND: The TC7662AEPA is a classic, highly reliable charge pump IC that delivers exceptional value. It solves the common problem of generating a negative voltage with minimal effort, component count, and cost, making it a perennial favorite among engineers for a vast array of applications.
Keywords: Charge Pump, Voltage Inverter, DC-DC Converter, Negative Voltage Generator, Switched Capacitor
