SNVS069E February   2000  – January 2022 LM2767

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 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Parameter Measurement Information
    1. 7.1 Test Circuit
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Positive Voltage Doubler
        2. 9.2.2.2 Capacitor Selection
        3. 9.2.2.3 Paralleling Devices
        4. 9.2.2.4 Cascading Devices
        5. 9.2.2.5 Regulating VOUT
      3. 9.2.3 Application Curve
  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 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.2.1 Positive Voltage Doubler

GUID-487D1E51-7B2E-41A7-88BC-AEE83DB38CCB-low.pngFigure 9-2 Voltage Doubling Principle

The output characteristics of this circuit can be approximated by an ideal voltage source in series with a resistance. The voltage source equals 2 V+. The output resistance Rout is a function of the ON resistance of the internal MOSFET switches, the oscillator frequency, and the capacitance and ESR of C1 and C2. Because the switching current charging and discharging C1 is approximately twice the output current, the effect of the ESR of the pumping capacitor C1 is multiplied by four in the output resistance. The output capacitor C2 is charging and discharging at a current approximately equal to the output current, therefore, its ESR only counts once in the output resistance. A good approximation of Rout is:

Equation 1. GUID-9DDAED56-F752-4B9A-B14C-4F768C405045-low.gif

where

  • RSW is the sum of the ON resistance of the internal MOSFET switches shown in Figure 9-2.

The peak-to-peak output voltage ripple is determined by the oscillator frequency as well as the capacitance and ESR of the output capacitor C2:

Equation 2. GUID-7537586C-170A-4C39-A5AD-26CD0E9E4082-low.gif

High capacitance, low ESR capacitors can reduce both the output resistance and the voltage ripple.

The Schottky diode D1 is only needed to protect the device from turning on its own parasitic diode and potentially latching up. During start-up, D1 also quickly charges up the output capacitor to VIN minus the diode drop thereby decreasing the start-up time. Therefore, the Schottky diode D1 must have enough current carrying capability to charge the output capacitor at start-up, as well as a low forward voltage to prevent the internal parasitic diode from turning on. A Schottky diode like 1N5817 can be used for most applications. If the input voltage ramp is less than 10 V/ms, a smaller Schottky diode like MBR0520LT1 can be used to reduce the circuit size.