SNVS002E January   1999  – October 2014 LM2662 , LM2663

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Handling Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Performance Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Changing Oscillator Frequency
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Simple Negative Voltage Converter
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Paralleling Devices
          2. 9.2.1.2.2 Cascading Devices
          3. 9.2.1.2.3 Regulating VOUT
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Positive Voltage Doubler
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 Application Curves
      3. 9.2.3 Splitting VIN in Half
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Detailed Design Procedure
        3. 9.2.3.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Related Links
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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8 Detailed Description

8.1 Overview

The LM2662/LM2663 contains four large CMOS switches which are switched in a sequence to invert the input supply voltage. Energy transfer and storage are provided by external capacitors. Figure 16 illustrates the voltage conversion scheme. When S1 and S3 are closed, C1 charges to the supply voltage V+. During this time interval switches S2 and S4 are open. In the second time interval, S1 and S3 are open and S2 and S4 are closed, C1 is charging C2. After a number of cycles, the voltage across C2 will be pumped to V+. Since the anode of C2 is connected to ground, the output at the cathode of C2 equals −(V+) assuming no load on C2, no loss in the switches, and no ESR in the capacitors. In reality, the charge transfer efficiency depends on the switching frequency, the on-resistance of the switches, and the ESR of the capacitors.

10000322.pngFigure 16. Voltage Inverting Principle

8.2 Functional Block Diagram

blockdiag.gif

8.3 Feature Description

8.3.1 Changing Oscillator Frequency

For the LM2662, the internal oscillator frequency can be selected using the Frequency Control (FC) pin. When FC is open, the oscillator frequency is 20 kHz; when FC is connected to V+, the frequency increases to 150 kHz. A higher oscillator frequency allows smaller capacitors to be used for equivalent output resistance and ripple, but increases the typical supply current from 0.3 mA to 1.3 mA.

The oscillator frequency can be lowered by adding an external capacitor between OSC and GND (See typical performance characteristics). Also, in the inverter mode, an external clock that swings within 100 mV of V+ and GND can be used to drive OSC. Any CMOS logic gate is suitable for driving OSC. LV must be grounded when driving OSC. The maximum external clock frequency is limited to 150 kHz.

The switching frequency of the converter (also called the charge pump frequency) is half of the oscillator frequency.

NOTE

OSC cannot be driven by an external clock in the voltage-doubling mode.

Table 1. LM2662 Oscillator Frequency Selection

FC OSC OSCILLATOR
Open Open 20 kHz
V+ Open 150 kHz
Open or V+ External Capacitor See Typical Performance Characteristics
N/A External Clock (inverter mode only) External Clock Frequency

Table 2. LM2663 Oscillator Frequency Selection

OSC OSCILLATOR
Open 150 kHz
External Capacitor See Typical Performance Characteristics
External Clock (inverter mode only) External Clock Frequency

8.4 Device Functional Modes

8.4.1 Shutdown Mode

For the LM2663, a shutdown (SD) pin is available to disable the device and reduce the quiescent current to 10 μA. Applying a voltage greater than 2 V to the SD pin will bring the device into shutdown mode. While in normal operating mode, the SD pin is connected to ground.