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The ICL7660 is a useful charge pump DC-DC converter IC for circuits that need a negative voltage from a single positive power supply. Instead of using an inductor, it works with external capacitors and internal switching circuits to invert, double, divide, or multiply voltage. This article explains the ICL7660 pinout, working principle, circuit operation, features, specifications, etc.
The ICL7660 is a monolithic CMOS switched-capacitor DC-DC converter IC used to convert a positive input voltage into other voltage levels. It can invert, double, divide, or multiply a DC input using a charge pump design, so it does not require an external inductor. The device is compatible with the industry-standard 7660 family and typically operates from 1.5V to 10V.
The ICL7660 uses an internal oscillator and power MOSFET switches to transfer charge between external capacitors. In its common voltage inverter configuration, it can generate a negative output voltage from a positive supply, such as producing about −5V from a +5V input. It offers low quiescent current, high efficiency for low-power circuits, and simple external component requirements.
| Pin No. | Pin Name | Function |
| 1 | BOOST (N.C. on ICL7660) | Used on some variants such as the MAX1044 to increase the internal oscillator frequency. On the standard ICL7660, this pin is typically not connected (N.C.). |
| 2 | CAP+ | Positive terminal for the external flying capacitor used by the charge pump circuit during voltage conversion. |
| 3 | GND | Ground reference for the device. Connect this pin to the system ground. |
| 4 | CAP− | Negative terminal for the external flying capacitor. Works with CAP+ to transfer charge during switching cycles. |
| 5 | VOUT | Output voltage pin. In a voltage inverter circuit, this pin provides the negative output voltage generated by the charge pump. |
| 6 | LV | Low-voltage mode control pin. It improves operation at lower supply voltages. For input voltages below approximately 3.5V, this pin is typically connected to GND. |
| 7 | OSC | Oscillator control pin. Allows adjustment of the internal switching frequency using external components or synchronization with an external clock. |
| 8 | V+ | Positive power supply input. Connect the input voltage source to this pin. |
• MAX1044
• TC7660
• MAX660
• LM2662
The functional block diagram illustrates the internal architecture of the ICL7660. An internal oscillator generates switching signals that control four MOSFET switches arranged as a charge pump network. These switches alternately connect the external flying capacitor to different nodes, allowing charge to be transferred efficiently between the input and output stages.
The diagram also shows the internal regulator, oscillator control circuitry, and the CAP+, CAP−, V+, and VOUT connections. Together, these blocks coordinate the charge transfer process that enables the device to invert or convert the input voltage without requiring an inductor. This design helps keep the circuit compact while maintaining high conversion efficiency.
The operating circuit diagram shows the typical external connections required for voltage inversion. A positive DC supply is connected to the V+ pin, while a flying capacitor is placed between CAP+ and CAP−. An output capacitor is connected between VOUT and ground to smooth the generated voltage and reduce ripple.
During operation, the ICL7660 transfers charge through the flying capacitor and delivers an output voltage with reversed polarity at the VOUT pin. For example, a +5V input can produce an output close to −5V under light-load conditions. The simple capacitor-based design eliminates the need for inductors, resulting in a low-cost and space-efficient negative voltage converter.
| Parameter | ICL7660 Specification |
| Device Type | CMOS Switched-Capacitor Voltage Converter (Charge Pump DC-DC Converter) |
| Main Functions | Voltage Inversion, Voltage Doubling, Voltage Division, Voltage Multiplication |
| Input Supply Voltage Range | 1.5V to 10V |
| Typical Power Conversion Efficiency | 98% |
| Voltage Conversion Efficiency | Up to 99.9% |
| Typical Supply Current | 80 µA |
| Maximum Supply Current | 175 µA (at +25°C) |
| Oscillator Frequency | Typically 10 kHz at V+ = 5V |
| Output Resistance | Typically 55 Ω (20 mA load, 5 kHz operation) |
| External Inductor Required | No |
| External Diode Required | No |
| Output Current Capability | Typically up to 10–20 mA (depending on operating conditions) |
| Operating Temperature Range | 0°C to +70°C (ICL7660C), -40°C to +85°C (ICL7660E), -55°C to +125°C (ICL7660M) |
| Storage Temperature Range | -65°C to +150°C |
| Maximum Supply Voltage | 10.5V |
| Short-Circuit Protection | Continuous output short-circuit operation when V+ ≤ 5.5V |
| Package Types | PDIP, SOIC, µMAX |
| Internal Components | Oscillator Control Circuitry and Four Power MOSFET Switches |
| Key Advantages | Low Quiescent Current, High Efficiency, Low Component Count, Compact Design |
In the first circuit, the DC input enters through the barrel jack and is regulated by the 7809 voltage regulator, which provides a stable +9V output. Capacitors C1 and C2 filter the input and output of the regulator to reduce noise and improve voltage stability. The regulated +9V supply is then connected to the V+ pin of the ICL7660.
The ICL7660 uses capacitor C3 as a flying capacitor to transfer charge between the CAP+ and CAP− pins. Through its internal oscillator and switching network, the device repeatedly charges and discharges C3, effectively reversing the polarity of the input voltage. As a result, the VOUT pin generates a negative voltage, producing approximately −9V relative to ground. Capacitor C4 filters the output and helps maintain a stable negative voltage with reduced ripple.
In the second circuit, a +5V input supply is connected directly to the ICL7660. The device uses capacitor C1 as the flying capacitor and capacitor C2 as the output filter capacitor. No voltage regulator is required because the input voltage is already suitable for the IC.
During operation, the ICL7660 converts the +5V input into an approximately −5V output. The output connector provides three terminals: +5V, −5V, and GND. This creates a simple dual power supply from a single positive voltage source. The circuit demonstrates how the ICL7660 can generate a negative rail while preserving the original positive supply, providing both voltage polarities from one input source.
The ICL7660 is commonly used to create a negative supply rail for op-amp circuits. This allows the amplifier to handle signals that swing below ground when only a single positive supply is available.
Some sensor interface circuits need a small negative voltage for accurate signal measurement or offset adjustment. The ICL7660 helps provide this negative rail with only a few external capacitors.
RS-232 interfaces require positive and negative voltage levels for proper signaling. The ICL7660 can help generate the negative voltage needed when the system only has a positive DC supply.
Certain LCD displays need a negative bias voltage to control contrast. The ICL7660 can generate this voltage without adding a bulky inductor-based converter.
The ICL7660 is useful in compact battery-powered equipment because it uses low quiescent current and requires few external components. It can create an extra voltage rail while keeping the circuit simple.
Audio filters, preamps, and analog processing circuits may need a negative rail to improve signal swing and reduce clipping around ground. The ICL7660 can provide this rail for low-current designs.
| Feature | ICL7660 | MAX660 | LM2662 |
| Manufacturer | Renesas/Intersil | Analog Devices/Maxim | Texas Instruments |
| Converter Type | Charge Pump Voltage Converter | Charge Pump Voltage Converter | Charge Pump Voltage Converter |
| Input Voltage Range | 1.5V to 10V | 1.5V to 5.5V | 2.5V to 5.5V |
| Main Functions | Invert, Double, Divide, Multiply | Invert, Double | Invert, Double |
| Typical Output Current | 10–20 mA | Up to 100 mA | Up to 200 mA |
| Typical Efficiency | Up to 98% | Up to 98% | Up to 95% |
| Oscillator Frequency | ~10 kHz | 10 kHz / 80 kHz (BOOST mode) | 150 kHz |
| External Inductor Required | No | No | No |
| External Diode Required | No | No | No |
| Output Ripple | Moderate | Lower than ICL7660 | Low |
| Quiescent Current | Very Low | Low | Low |
| Component Count | Very Low | Low | Low |
| Best For | Low-current negative voltage generation | Higher-current charge pump applications | Compact high-frequency voltage conversion |
| Advantages | Wide input range, simple design, low power consumption | Higher output current, BOOST pin, improved performance | Higher switching frequency, smaller capacitors, better output capability |
| Limitations | Limited output current | Narrower input voltage range | Lower maximum input voltage than ICL7660 |
| Typical Applications | Op-amp supplies, LCD bias, RS-232 interfaces | Analog power supplies, portable equipment | Portable electronics, sensor systems, low-noise power rails |
The ICL7660’s switched-capacitor design makes it easy to use because it does not need an external inductor or complex power circuit. With a wide operating voltage range, low supply current, and high efficiency in low-current designs, it remains a reliable option for simple voltage inversion tasks. However, the ICL7660 is not designed for heavy loads. Its output current is limited, and the output voltage can drop when the load increases. For circuits that need higher current, alternatives such as the MAX660 or LM2662 may be more suitable.
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