SNVS099I May   1999  – October 2016 LM2991

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 ON/Off Pin
      2. 7.3.2 Forcing The Output Positive
      3. 7.3.3 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operation with VOUT(TARGET) -5 V ≥ VIN > -26 V
  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
        2. 8.2.2.2 Ceramic Bypass Capacitors
        3. 8.2.2.3 Minimum Load
        4. 8.2.2.4 Setting The Output Voltage
        5. 8.2.2.5 Power Dissipation
        6. 8.2.2.6 Estimating Junction Temperature
      3. 8.2.3 Application Curves
      4. 8.2.4 Additional Application Circuits
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Device Nomenclature
    2. 11.2 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 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 LM2991 is a five-pin, low-dropout, 1-A negative adjustable voltage regulator and negative power supply, ideally suited for a dual-supply system when using together with LM2941 series. The device may also be used as an adjustable current-sink load.

7.2 Functional Block Diagram

LM2991 1126008.png

7.3 Feature Description

7.3.1 ON/Off Pin

The LM2991 regulator can be turned off by applying a TTL or CMOS level high signal to the ON/OFF pin. The impedance of the voltage source driving the ON/OFF pin must be low enough to source the ON/OFF pin input current to meet the OFF threshold voltage level, 100 µA maximum at 2.4 V.

If the ON/OFF function is not needed, connect the pin to GND. The ON/OFF pin should not be left floating, as this is not an ensured operating condition. See Figure 15.

7.3.2 Forcing The Output Positive

Due to an internal clamp circuit, the LM2991 can withstand positive voltages on its output. If the voltage source pulling the output positive is DC, the current must be limited to 1.5 A. A current over 1.5 A fed back into the LM2991 could damage the device. The LM2991 output can also withstand fast positive voltage transients up to 26 V, without any current limiting of the source. However, if the transients have a duration of over 1 ms, the output should be clamped with a Schottky diode to ground.

7.3.3 Thermal Shutdown

The LM2991 has an internally set thermal shutdown point of typically 160°C, with approximately 10°C of hysteresis. This thermal shutdown temperature point is outside the specified Recommended Operating Conditions range, above the Absolute Maximum Ratings, and is intended as a safety feature for momentary fault conditions only. Avoid continuous operation near the thermal shutdown temperature as it may have a negative affect on the life of the device.

7.4 Device Functional Modes

7.4.1 Operation with VOUT(TARGET) –5 V ≥ VIN > –26 V

The device operates if the input voltage is within VOUT(TARGET) –5 V to –26 V range. At input voltages beyond the VIN requirement, the devices do not operate correctly, and output voltage may not reach target value.