**ADM660AN: A Comprehensive Guide to the Switched-Capacitor Voltage Converter**

In the realm of electronic design, generating a negative voltage or doubling an existing supply from a single positive source is a common challenge. The **ADM660AN**, a monolithic switched-capacitor voltage converter from Analog Devices, provides an elegant and efficient solution. This integrated circuit (IC) is renowned for its simplicity, compactness, and ability to perform both voltage inversion and multiplication with minimal external components.

**Understanding the Core Technology: Switched-Capacitor Conversion**

Unlike traditional inductor-based switching regulators, the ADM660AN utilizes a **switched-capacitor charge pump** mechanism. This method relies on the transfer of charge between capacitors controlled by internal switches, which are toggled by a high-frequency oscillator. The fundamental process involves two phases:

1. **Charge Phase:** An external "flying" capacitor is connected across the input voltage source, allowing it to charge to the value of V+.

2. **Pump Phase:** The internal switches reconfigure, disconnecting the flying capacitor from the input and connecting it in series with the input source and a storage capacitor. This action effectively **inverts the input voltage** to create a negative output (V- ≈ -V+) or doubles it (Vout ≈ 2 x V+), depending on the pin configuration.

This switching action occurs at a high frequency (typically several kHz), creating a regulated output through capacitive charge transfer rather than magnetic energy storage.

**Key Features and Specifications of the ADM660AN**

The ADM660AN stands out due to its robust feature set tailored for space-constrained and noise-sensitive applications:

* **Wide Input Voltage Range:** It operates from a single supply voltage between **+1.5V to +7.0V**, making it compatible with common voltage levels like 3.3V and 5V.

* **Dual Functionality:** It can be easily configured as a **voltage inverter** to generate a negative supply (e.g., -5V from +5V) or as a **voltage doubler** (e.g., +10V from +5V).

* **Low Power Consumption:** The CMOS construction ensures low quiescent current, which is crucial for battery-powered devices.

* **Minimal External Components:** The circuit requires only two external capacitors (a flying capacitor and a reservoir capacitor) to function, significantly reducing the PCB footprint and Bill of Materials (BOM) cost.

* **Precision Oscillator:** The device includes an internal oscillator, but it also provides an **OSC (oscillator control) pin** for external frequency synchronization or to slow the internal oscillator, reducing supply current and output ripple.

**Typical Application Circuits**

1. **Voltage Inverter:** This is the most common application. The input voltage (e.g., +5V) is applied to V+. The flying capacitor (C1) is connected between pins CAP+ and CAP-. The output capacitor (C2) is placed from Vout to ground. In this mode, the output at Vout will be approximately -5V.

2. **Voltage Doubler:** To configure the ADM660AN as a doubler, the Vout pin is connected to ground. The doubled output is then taken from the CAP- pin. The flying capacitor (C1) is connected between CAP+ and CAP-, and the output capacitor (C2) is placed from CAP- to ground. This setup generates an output voltage of approximately +10V from a +5V input.

**Critical Design Considerations**

While simple to use, optimal performance requires attention to detail:

* **Capacitor Selection:** Low-ESR (Equivalent Series Resistance) ceramic capacitors are highly recommended for both the flying and output capacitors. Their low ESR minimizes losses and improves efficiency and regulation. Typical values range from **1μF to 10μF**.

* **Output Current and Ripple:** The switched-capacitor architecture inherently produces a higher output ripple compared to inductor-based regulators. The magnitude of this ripple is inversely proportional to the value of the output capacitor. For applications requiring higher output current (up to 50-100mA) or lower noise, increasing the value of the output capacitor or adding a small LC filter at the output can be highly effective.

* **PCB Layout:** To minimize noise and ensure stability, the path connecting the IC's CAP+, CAP-, and Vout pins to their respective capacitors should be as **short and direct as possible**. This reduces parasitic inductance and resistance that can degrade performance.

**ICGOODFIND**

The **ADM660AN** is an exceptionally versatile and user-friendly IC that simplifies power management design. Its ability to generate negative or doubled voltages with just two capacitors makes it an indispensable component for a wide array of applications, including operational amplifier power supplies, data acquisition systems, LCD bias generators, and portable battery-operated equipment. Its blend of simplicity, functionality, and compactness secures its status as a classic solution in the engineer's toolkit.

**Keywords:**

1. **Switched-Capacitor**

2. **Voltage Inverter**

3. **Charge Pump**

4. **Negative Voltage Generator**

5. **Minimal External Components**