SBVS304A June   2017  – November 2017 TPS7A83A

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configurations 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 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. 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 Recommended Capacitor Types
        6. 8.1.1.6 Input and Output Capacitor Requirements (CIN and COUT)
        7. 8.1.1.7 Feed-Forward Capacitor (CFF)
        8. 8.1.1.8 Noise-Reduction and Soft-Start Capacitor (CNR/SS)
      2. 8.1.2 Start-Up
        1. 8.1.2.1 Soft-Start (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
      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 Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
  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. 11.1.2 Device Nomenclature
    2. 11.2 Documentation Support
      1. 11.2.1 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

Detailed Description

Overview

The TPS7A83A is a high-current (2 A), low-noise (4.4 µVRMS), high-accuracy (0.75%), low-dropout linear voltage regulator (LDO). These features make the device a robust solution to solve many challenging problems in generating a clean, accurate power supply.

The TPS7A83A has several features that make the device useful in a variety of applications. Table 1 categorizes the functionalities shown in the Functional Block Diagram section.

Table 1. Features

VOLTAGE REGULATION SYSTEM START-UP INTERNAL PROTECTION
High accuracy Programmable soft-start Foldback current limit
Low-noise, high-PSRR output No sequencing requirement between BIAS, IN, and EN Thermal shutdown
Fast transient response Power-good output
Start-up with negative bias on OUT

Overall, these features make the TPS7A83A the component of choice because of the versatility and ability of the device to generate a supply for most applications.

Functional Block Diagram

TPS7A83A fbd_sbvs291.gif

NOTE:

For the ANY-OUT network, the ratios between the values are highly accurate as a result of matching, but the actual resistance can vary significantly from the numbers listed.

Feature Description

Voltage Regulation Features

DC Regulation

As Figure 43 shows, an LDO functions as a class-B amplifier in which the input signal is the internal reference voltage (VREF). VREF is designed to have a very low bandwidth at the input to the error amplifier through the use of a low-pass filter (VNR/SS).

As such, the reference can be considered as a pure dc input signal. The low output impedance of an LDO comes from the combination of the output capacitor and pass element. The pass element also presents a high input impedance to the source voltage when operating as a current source. A positive LDO can only source current because of the class-B architecture.

This device achieves a maximum of 0.75% output voltage accuracy primarily because of the high-precision band-gap voltage (VBG) that creates VREF. The low dropout voltage (VDO) reduces the thermal power dissipation required by the device to regulate the output voltage at a given current level, thereby improving system efficiency. These features combine to make this device a good approximation of an ideal voltage source.

TPS7A83A fb_ldo_classb_sbvs291.gif

NOTE:

VOUT = VREF × (1 + R1 / R2).
Figure 43. Simplified Regulation Circuit

AC and Transient Response

The LDO responds quickly to a transient (large-signal response) on the input supply (line transient) or the output current (load transient) resulting from the LDO high-input impedance and low output-impedance across frequency. This same capability also means that the LDO has a high power-supply rejection ratio (PSRR) and, when coupled with a low internal noise-floor (en), the LDO approximates an ideal power supply in ac (small-signal) and large-signal conditions.

The choice of external component values optimizes the small- and large-signal response. The NR/SS capacitor (CNR/SS) and feed-forward capacitor (CFF) easily reduce the device noise floor and improve PSRR; see Optimizing Noise and PSRR for more information on optimizing the noise and PSRR performance.

System Start-Up Features

In many different applications, the power-supply output must turn on within a specific window of time to either ensure proper operation of the load or to minimize the loading on the input supply or other sequencing requirements. The LDO start-up is well-controlled and user-adjustable, solving the demanding requirements faced by many power-supply design engineers in a simple fashion.

Programmable Soft-Start (NR/SS)

Soft-start directly controls the output start-up time and indirectly controls the output current during start-up (in-rush current).

Figure 44 shows that the external capacitor at the NR/SS pin (CNR/SS) sets the output start-up time by setting the rise time of the internal reference (VNR/SS).

TPS7A83A ai_softstart_sbvs291.gif Figure 44. Simplified Soft-Start Circuit

Internal Sequencing

Controlling when a single power supply turns on can be difficult in a power distribution network (PDN) because of the high power levels inherent in a PDN, and the variations between all of the supplies. Figure 45 and Table 2 show how the LDO turnon and turnoff time are set by the enable circuit (EN) and undervoltage lockout circuits (UVLO1,2(IN) and UVLOBIAS).

TPS7A83A ai_en_circuit_sbvs291.gif Figure 45. Simplified Turnon Control

Table 2. Internal Sequencing Functionality Table

INPUT VOLTAGE BIAS VOLTAGE ENABLE STATUS LDO STATUS ACTIVE DISCHARGE POWER GOOD
VIN ≥ VUVLO_1,2(IN) VBIAS ≥ VUVLO(BIAS) EN = 1 On Off PG = 1 when VOUT ≥ VIT(PG)
EN = 0 Off On PG = 0
VBIAS < VUVLO(BIAS) + VHYS(BIAS) EN = don't care Off On (1)
VIN < VUVLO_1,2(IN) – VHYS1,2(IN) BIAS = don't care Off
IN = don't care VBIAS ≥ VUVLO(BIAS) Off
The active discharge remains on as long as VIN or VBIAS provide enough headroom for the discharge circuit to function.

Enable (EN)

The enable signal (VEN) is an active-high digital control that enables the LDO when the enable voltage is past the rising threshold (VEN ≥ VIH(EN)) and disables the LDO when the enable voltage is below the falling threshold (VEN ≤ VIL(EN)). The exact enable threshold is between VIH(EN) and VIL(EN) because EN is a digital control. Connect EN to VIN or VBIAS if enable functionality is not desired.

Undervoltage Lockout (UVLO) Control

The UVLO circuits respond quickly to glitches on IN or BIAS and attempts to disable the output of the device if either of these rails collapse.

The local input capacitance prevents severe brownouts in most applications; see the Undervoltage Lockout (UVLO) section for more details.

Active Discharge

When either EN or UVLO is low, the device connects a resistor of several hundred ohms from VOUT to GND, discharging the output capacitance.

Do not rely on the active discharge circuit for discharging large output capacitors when the input voltage drops below the targeted output voltage. Current flows from the output to the input (reverse current) when VOUT > VIN, which can cause damage to the device (when VOUT > VIN + 0.3 V); see the Reverse Current section for more details.

Power-Good Output (PG)

The PG signal provides an easy solution to meet demanding sequencing requirements because PG signals when the output nears the nominal value. PG can be used to signal other devices in a system when the output voltage is near, at, or above the set output voltage (VOUT(nom)). Figure 46 shows a simplified schematic.

The PG signal is an open-drain digital output that requires a pullup resistor to a voltage source and is active high. The PG circuit sets the PG pin into a high-impedance state to indicate that the power is good.

Using a large feed-forward capacitor (CFF) delays the output voltage and, because the PG circuit monitors the FB pin, the PG signal can indicate a false positive. A simple solution to this scenario is to use an external voltage detector device, such as the TPS3890; see the Feed-Forward Capacitor (CFF) section for more information.

TPS7A83A ai_pg_circuit_sbvs291.gif Figure 46. Simplified PG Circuit

Internal Protection Features

In many applications, fault events can occur that damage devices in the system. Short circuits and excessive heat are the most common fault events for power supplies. The TPS7A83A implements circuitry to protect the device and its load during these events. Continuously operating in these fault conditions or above a junction temperature of 125°C is not recommended because the long-term reliability of the device is reduced.

Foldback Current Limit (ICL)

The internal current limit circuit is used to protect the LDO against high load-current faults or shorting events. During a current-limit event, the LDO sources constant current; therefore, the output voltage falls with decreased load impedance. Thermal shutdown can activate during a current limit event because of the high power dissipation typically found in these conditions. To ensure proper operation of the current limit, minimize the inductances to the input and load. Continuous operation in current limit is not recommended.

Thermal Protection (Tsd)

The thermal shutdown circuit protects the LDO against excessive heat in the system, either resulting from current limit or high ambient temperature.

The output of the LDO turns off when the LDO temperature (junction temperature, TJ) exceeds the rising thermal shutdown temperature. The output turns on again after TJ decreases below the falling thermal shutdown temperature.

A high power dissipation across the device, combined with a high ambient temperature (TA), can cause TJ to be greater than or equal to Tsd, triggering the thermal shutdown and causing the output to fall to 0 V. The LDO can cycle on and off when thermal shutdown is reached under these conditions.

Continuously triggering thermal shutdown can degrade long-term reliability.

Device Functional Modes

Table 3 provides a quick comparison between the regulation and disabled operation.

Table 3. Device Functional Modes Comparison

OPERATING MODE PARAMETER
VIN VBIAS EN IOUT TJ
Regulation(1) VIN > VOUT(nom) + VDO VBIAS ≥ VUVLO(BIAS)(3) VEN > VIH(EN) IOUT < ICL TJ ≤ TJ(maximum)
Disabled(2) VIN < VUVLO_1,2(IN) VBIAS < VUVLO(BIAS) VEN < VIL(EN) TJ > Tsd
Current-limit operation IOUT ≥ ICL
All table conditions must be met.
The device is disabled when any condition is met.
VBIAS is only required for VIN < 1.4 V.

Regulation

The device regulates the output to the nominal output voltage when all the conditions in Table 3 are met.

Disabled

When disabled, the pass device is turned off, the internal circuits are shut down, and the output voltage is actively discharged to ground by an internal resistor from the output to ground. See the Active Discharge section for additional information.