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The LM2660M is a CMOS charge-pump voltage converter manufactured by National Semiconductor (NS).

Specifications:

• Input Voltage Range: 1.5V to 5.5V
• Output Voltage Options:
• Doubles input voltage (e.g., 3V to 6V)
• Inverts input voltage (e.g., 5V to -5V)
• Output Current: Up to 40mA (with minimal voltage drop)
• Switching Frequency: 160kHz (typical)
• Low Quiescent Current: 300µA (typical)
• Efficiency: Up to 90% (depending on load and configuration)
• Operating Temperature Range: -40°C to +85°C
• Package: 8-pin SOIC (M)

Descriptions:

The LM2660M is a versatile switched-capacitor voltage converter that can generate either a doubled or inverted output voltage from a single supply. It requires minimal external components (only two flying capacitors and two optional reservoir capacitors). The device operates efficiently across a wide input range, making it suitable for battery-powered applications.

Features:

• Simple Voltage Conversion: Doubles or inverts input voltage with no inductors.
• Low Power Consumption: Ideal for portable and battery-operated devices.
• No Diode Voltage Loss: Unlike inductor-based converters.
• Built-In Oscillator: No external timing components required.
• Shutdown Mode: Reduces current consumption to <1µA when disabled.
• Space-Saving Design: Requires only capacitors for operation.

This information is based strictly on the manufacturer's specifications for the LM2660M.

# LM2660M: Practical Applications, Design Considerations, and Implementation

## Practical Application Scenarios

The LM2660M is a switched-capacitor voltage converter from Texas Instruments (formerly National Semiconductor) capable of generating both positive and negative supply rails. Its versatility makes it suitable for several applications:

1. Voltage Inversion – The device efficiently converts a positive input voltage (e.g., +5V) to a corresponding negative output (-5V), useful in analog signal conditioning, op-amp biasing, and data acquisition systems.

2. Voltage Doubling – By configuring the LM2660M in boost mode, it can double an input voltage (e.g., 3V to 6V), supporting low-power microcontrollers or sensors in battery-operated devices.

3. Portable and Battery-Powered Systems – Due to its low quiescent current (~200µA), the LM2660M is ideal for handheld instruments, IoT devices, and medical wearables where power efficiency is critical.

4. Noise-Sensitive Applications – Unlike inductive converters, the LM2660M’s charge-pump architecture minimizes EMI, making it suitable for RF circuits and precision measurement systems.

## Common Design-Phase Pitfalls and Avoidance Strategies

1. Insufficient Input/Output Capacitance – The LM2660M requires proper capacitor selection (typically 10µF low-ESR types) for stability. Undersized capacitors can lead to excessive ripple or oscillation.

• Solution: Follow the datasheet recommendations for input/output capacitors and verify performance under load transients.

2. Thermal Management in High-Current Applications – The device can deliver up to 40mA, but excessive current draw increases power dissipation, potentially triggering thermal shutdown.

• Solution: Ensure adequate PCB copper area for heat dissipation or consider an external MOSFET-based solution for higher currents.

3. Improper Layout Practices – Poor placement of capacitors or long traces increases parasitic inductance, degrading efficiency and noise performance.

• Solution: Place input/output capacitors close to the IC and use short, wide traces for high-current paths.

4. Unstable Operation with Light Loads – The LM2660M may exhibit instability if the load current is too low (<1mA).

• Solution: Add a dummy load resistor or use a higher switching frequency variant (if available) to maintain regulation.

## Key Technical Considerations for Implementation

1. Switching Frequency Selection – The LM2660M operates at 20kHz (default) or 100kHz (with external clock). Lower frequencies reduce noise but require larger capacitors, while higher frequencies allow smaller components at the cost of increased EMI.

2. Input Voltage Range – The device supports 1.5V to 5.5V, making it compatible with Li-ion batteries and 3.3V/5V logic supplies. Exceeding 5.5V may damage the IC.

3. Output Current Limitations – Efficiency drops significantly above 20mA; verify load requirements before implementation.

4. Start-Up Behavior – The LM2660M exhibits inrush current during start-up; ensure the power source can handle transient demands.

By addressing these factors, designers can leverage the LM2660