SBVS291C April   2017  – December 2020 TPS7A84A

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: General
    6. 6.6 Electrical Characteristics: TPS7A8400A
    7. 6.7 Electrical Characteristics: TPS7A8401A
    8. 6.8 Typical Characteristics: TPS7A8400A
    9. 6.9 Typical Characteristics: TPS7A8401A
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 Voltage Regulation Features
        1. 7.3.1.1 DC Regulation
        2. 7.3.1.2 AC and Transient Response
      2. 7.3.2 System Start-Up Features
        1. 7.3.2.1 Programmable Soft Start (NR/SS)
        2. 7.3.2.2 Internal Sequencing
          1. 7.3.2.2.1 Enable (EN)
          2. 7.3.2.2.2 Undervoltage Lockout (UVLO) Control
          3. 7.3.2.2.3 Active Discharge
        3. 7.3.2.3 Power-Good Output (PG)
      3. 7.3.3 Internal Protection Features
        1. 7.3.3.1 Foldback Current Limit (ICL)
        2. 7.3.3.2 Thermal Protection (Tsd)
    4. 7.4 Device Functional Modes
      1. 7.4.1 Regulation
      2. 7.4.2 Disabled
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 External Component Selection
        1. 8.1.1.1 Adjustable Operation
        2. 8.1.1.2 ANY-OUT Programmable Output Voltage
        3. 8.1.1.3 ANY-OUT Operation
        4. 8.1.1.4 Increasing ANY-OUT Resolution for LILO Conditions
        5. 8.1.1.5 Current Sharing
        6. 8.1.1.6 Recommended Capacitor Types
        7. 8.1.1.7 Input and Output Capacitor Requirements (CIN and COUT)
        8. 8.1.1.8 Feed-Forward Capacitor (CFF)
        9. 8.1.1.9 Noise-Reduction and Soft-Start Capacitor (CNR/SS)
      2. 8.1.2 Start-Up
        1. 8.1.2.1 Circuit Soft-Start Control (NR/SS)
          1. 8.1.2.1.1 Inrush Current
        2. 8.1.2.2 Undervoltage Lockout (UVLO)
        3. 8.1.2.3 Power-Good (PG) Function
      3. 8.1.3 AC and Transient Performance
        1. 8.1.3.1 Power-Supply Rejection Ratio (PSRR)
        2. 8.1.3.2 Output Voltage Noise
        3. 8.1.3.3 Optimizing Noise and PSRR
          1. 8.1.3.3.1 Charge Pump Noise
        4. 8.1.3.4 Load Transient Response
      4. 8.1.4 DC Performance
        1. 8.1.4.1 Output Voltage Accuracy (VOUT)
        2. 8.1.4.2 Dropout Voltage (VDO)
          1. 8.1.4.2.1 Behavior When Transitioning From Dropout Into Regulation
      5. 8.1.5 Sequencing Requirements
      6. 8.1.6 Negatively Biased Output
      7. 8.1.7 Reverse Current Protection
      8. 8.1.8 Power Dissipation (PD)
        1. 8.1.8.1 Estimating Junction Temperature
        2. 8.1.8.2 Recommended Area for Continuous Operation (RACO)
    2. 8.2 Typical Applications
      1. 8.2.1 Low-Input, Low-Output (LILO) Voltage Conditions
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
  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 Development Support
        1. 11.1.1.1 Evaluation Models
        2. 11.1.1.2 Spice Models
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary

Package Options

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

8.1.3.3 Optimizing Noise and PSRR

The ultra-low noise floor and PSRR of the device can be improved in several ways, as described in Table 8-9.

Table 8-9 Effect of Various Parameters on AC Performance(1)(2)
PARAMETERNOISEPSRR
LOW-FREQUENCYMID-FREQUENCYHIGH-FREQUENCYLOW-FREQUENCYMID-FREQUENCYHIGH-FREQUENCY
CNR/SS+++No effectNo effect++++No effect
CFF++++++++++++
COUTNo effect++++No effect++++
VIN – VOUT+++++++++++
PCB layout++++++++++++
(1) The number of +'s indicates the improvement in noise or PSRR performance by increasing the parameter value.
(2) Shaded cells indicate the easiest improvement to noise or PSRR performance.

The noise-reduction capacitor, in conjunction with the noise-reduction resistor, forms a low-pass filter (LPF) that filters out the noise from the reference before being gained up with the error amplifier, thereby minimizing the output voltage noise floor. The LPF is a single-pole filter, and the cutoff frequency can be calculated with Equation 10. The typical value of RNR/SS is 250 kΩ. The effect of the CNR/SS capacitor increases when VOUT(nom) increases because the noise from the reference is gained up when the output voltage increases. For low-noise applications, TI recommends a 10-nF to 10-µF CNR/SS.

Equation 10. fcutoff = 1 / (2 × π × RNR/SS × CNR/SS)

The feed-forward capacitor reduces output voltage noise by filtering out the mid-band frequency noise. The feed-forward capacitor can be optimized by placing a pole-zero pair near the edge of the loop bandwidth and pushing out the loop bandwidth, thus improving mid-band PSRR.

A larger COUT or multiple output capacitors reduces high-frequency output voltage noise and PSRR by reducing the high-frequency output impedance of the power supply.

Additionally, a higher input voltage improves the noise and PSRR because greater headroom is provided for the internal circuits. However, a high power dissipation across the die increases the output noise because of the increase in junction temperature.

Good PCB layout improves the PSRR and noise performance by providing heat sinking at low frequencies and isolating VOUT at high frequencies.

Table 8-10 lists the output voltage noise for the 10-Hz to 100-kHz band at a 5-V output for a variety of conditions with an input voltage of 5.5 V and a load current of 3 A. The 5-V output was chosen as a worst-case nominal operation for output voltage noise.

Table 8-10 Output Noise Voltage at a 5-V Output (TPS7A8400A)
OUTPUT VOLTAGE NOISE (µVRMS)CNR/SS (nF)CFF (nF)COUT (µF)
11.7101047 || 10 || 10
7.71001047 || 10 || 10
610010047 || 10 || 10
7.4100101000
5.81001001000