SNVS311D May   2005  – February 2015 LP3878-ADJ

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 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Shutdown Input Operation
      2. 7.3.2 Reverse Input-Output Voltage
      3. 7.3.3 Low Output Noise
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operation With VOUT(TARGET) + 2 V ≤ VIN ≤ 16 V
      2. 7.4.2 Operation With SHUTDOWN Pin Control
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 External Capacitors
          1. 8.2.2.1.1 Input Capacitor
          2. 8.2.2.1.2 Output Capacitor
          3. 8.2.2.1.3 Noise Bypass Capacitor
        2. 8.2.2.2 Feedforward Capacitor
        3. 8.2.2.3 Capacitor Characteristics
          1. 8.2.2.3.1 Ceramic
        4. 8.2.2.4 Setting the Output Voltage
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Power Dissipation
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7 Detailed Description

7.1 Overview

The LP3878-ADJ is an adjustable regulator; the output voltage can be set from 1 V to 5.5 V. The device can deliver 800-mA continuous load current. Standard regulator features, such as overcurrent and overtemperature protection, are also included.

The LP3878-ADJ contains other features:

  • Low power shutdown current and low ground pin current
  • Very low output noise
  • 8-lead SO PowerPAD or WSON surface-mount packages to allow for increased power dissipation.

7.2 Functional Block Diagram

LP3878-ADJ 20120901.gif

7.3 Feature Description

7.3.1 Shutdown Input Operation

The LP3878-ADJ is shut off by pulling the SHUTDOWN input low, and turned on by pulling it high. If this feature is not to be used, the SHUTDOWN input should be tied to VIN to keep the regulator output on at all times.

To assure proper operation, the signal source used to drive the SHUTDOWN input must be able to swing above and below the specified turnon or turnoff voltage thresholds listed in the Electrical Characteristics under VON/OFF.

7.3.2 Reverse Input-Output Voltage

The PNP power transistor used as the pass element in the LP3878-ADJ contains a parasitic diode between the IN pin and the OUT pin. During normal operation (where the IN pin voltage is higher than the OUT pin voltage) this parasitic diode is reverse-biased. However, if the OUT pin voltage is pulled above the IN pin voltage this diode will turn ON, and current will flow into the LP3878-ADJ OUT pin.

In such cases, a parasitic SCR between the IN pin and the GND pin can latch ON which will allow a high current to flow from the VIN supply, into the IN pin to ground, which can damage the part. In any application where the OUT pin voltage may be higher than the IN pin voltage, even momentarily, an external Schottky diode must be connected from the IN pin to the OUT pin (cathode to IN pin, anode to OUT pin), to limit the reverse voltage across the LP3878-ADJ to 0.3 V (see Absolute Maximum Ratings).

7.3.3 Low Output Noise

With a 10-nF capacitor on the BYPASS pin, the output noise is only 18 µV.

7.4 Device Functional Modes

7.4.1 Operation With VOUT(TARGET) + 2 V ≤ VIN ≤ 16 V

The device operates if the input voltage is equal to, or exceeds VOUT(TARGET) + 2 V. At input voltages below the minimum VIN requirement, the device does not operate correctly and output voltage may not reach target value.

7.4.2 Operation With SHUTDOWN Pin Control

LP3878-ADJ is turned off by pulling the SHUTDOWN pin low, and turned on by pulling it high. If this feature is not used, the SHUTDOWN pin should be tied to VIN to keep the regulator output on at all times. To assure proper operation, the signal source used to drive the SHUTDOWN input must be able to swing above and below the specified turnon and turnoff voltage thresholds listed in the Electrical Characteristics under VL and VH.