SBVS179B December   2011  – August 2015 TPS7A8101

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Internal Current Limit
      2. 7.3.2 Shutdown
      3. 7.3.3 Start-Up
      4. 7.3.4 Undervoltage Lock-Out (UVLO)
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Recommended Component Values
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
        1. 8.2.1.1 Dropout Voltage
        2. 8.2.1.2 Minimum Load
        3. 8.2.1.3 Input and Output Capacitor Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Output Noise
        2. 8.2.2.2 Transient Response
      3. 8.2.3 Application Curve
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Board Layout Recommendations to Improve PSRR and Noise Performance
    2. 10.2 Layout Example
    3. 10.3 Thermal Protection
    4. 10.4 Power Dissipation
    5. 10.5 Estimating Junction Temperature
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Device Nomenclature
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

7 Detailed Description

7.1 Overview

The TPS7A8101 device belongs to a family of new-generation LDO regulators that use innovative circuitry to achieve wide bandwidth and high loop gain, resulting in extremely high PSRR (over a 1-MHz range) even with very low headroom (VI – VO). A noise-reduction capacitor (C(NR)) at the NR pin and a bypass capacitor (C(BYPASS)) decrease noise generated by the bandgap reference to improve PSRR, while a quick-start circuit fast-charges the noise-reduction capacitor. This family of regulators offers sub-bandgap output voltages, current limit, and thermal protection, and is fully specified from –40°C to 125°C.

7.2 Functional Block Diagram

TPS7A8101 fbd_adjust_bvs179.gifFigure 30. Functional Block Diagram

7.3 Feature Description

7.3.1 Internal Current Limit

The TPS7A8101 internal current limit helps protect the regulator during fault conditions. During current limit, the output sources a fixed amount of current that is largely independent of output voltage. For reliable operation, the device should not be operated in a current limit state for extended periods of time.

The PMOS pass element in the TPS7A8101 has a built-in body diode that conducts current when the voltage at OUT exceeds the voltage at IN. This current is not limited, so if extended reverse voltage operation is anticipated, external limiting may be appropriate.

7.3.2 Shutdown

The enable pin (EN) is active high and is compatible with standard and low voltage, TTL-CMOS levels. When shutdown capability is not required, EN can be connected to IN.

7.3.3 Start-Up

Through a lower resistance, the bandgap reference can quickly charge the noise reduction capacitor (CNR). The TPS7A8101 has a quick-start circuit to quickly charge CNR, if present; see the . At start-up, this quick-start switch is closed, with only 33 kΩ of resistance between the bandgap reference and the NR pin. The quick-start switch opens approximately 100 ms after any device enabling event, and the resistance between the bandgap reference and the NR pin becomes higher in value (approximately 250 kΩ) to form a very good low-pass (RC) filter. This low-pass filter achieves very good noise reduction for the reference voltage.

Inrush current can be a problem in many applications. The 33-kΩ resistance during the start-up period is intentionally put there to slow down the reference voltage ramp up, thus reducing the inrush current. For example, the capacitance of connecting the recommended CNR value of 0.47 μF along with the 33-kΩ resistance causes approximately 80-ms RC delay. Start-up time with the other CNR values can be calculated as:

Equation 1. TPS7A8101 q_tstr_bvs135.gif

Although the noise reduction effect is nearly saturated at 0.47 μF, connecting a CNR value greater than 0.47 μF can help reduce noise slightly more; however, start-up time will be extremely long because the quick-start switch opens after approximately 100 ms. That is, if CNR is not fully charged during this 100-ms period, CNR finishes charging through a higher resistance of 250 kΩ, and takes much longer to fully charge.

A low leakage CNR should be used; most ceramic capacitors are suitable.

7.3.4 Undervoltage Lock-Out (UVLO)

The TPS7A8101 uses an undervoltage lock-out circuit to keep the output shut off until the internal circuitry is operating properly. The UVLO circuit has a de-glitch feature so that it typically ignores undershoot transients on the input if they are less than 50-μs duration.

7.4 Device Functional Modes

Driving the EN pin over 1.2 V for VI from 2.2 V to 3.6 V or 1.35 V for VI from 3.6 V to 6.5 V turns on the regulator. Driving the EN pin below 0.4 V causes the regulator to enter shutdown mode.

In shutdown, the current consumption of the device is reduced to 0.02 µA typically.