SBVS204F June   2012  – September 2014

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 Handling 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 Internal Current Limit (ICL)
      2. 7.3.2 Enable (EN) And Under-Voltage Lockout (UVLO)
      3. 7.3.3 Soft-Start And Inrush Current
    4. 7.4 Device Functional Modes
    5. 7.5 Programming
      1. 7.5.1 ANY-OUT Programmable Output Voltage
      2. 7.5.2 Adjustable Operation (TPS7A4701 Only)
  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 Capacitor Recommendations
          1. 8.2.2.1.1 Input and Output Capacitor Requirements
          2. 8.2.2.1.2 Noise Reduction Capacitor (CNR)
        2. 8.2.2.2 Dropout Voltage (VDO)
        3. 8.2.2.3 Output Voltage Accuracy
        4. 8.2.2.4 Startup
        5. 8.2.2.5 AC Performance
          1. 8.2.2.5.1 Power-Supply Rejection Ratio (PSRR)
          2. 8.2.2.5.2 Load Step Transient Response
          3. 8.2.2.5.3 Noise
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
    1. 9.1 Power Dissipation (PD)
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Protection
    4. 10.4 Estimating Junction Temperature
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Related Links
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ

7 Detailed Description

7.1 Overview

The TPS7A4700 and TPS7A4701 (TPS7A470x) are positive voltage (+36 V), ultralow-noise (4 µVRMS) LDOs capable of sourcing a 1-A load. The TPS7A470x is designed with bipolar technology primarily for high-accuracy, high-precision instrumentation applications where clean voltage rails are critical to maximize system performance. This feature makes the device ideal for powering operational amplifiers, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and other high-performance analog circuitry.

7.2 Functional Block Diagram

fbd_bvs204.gif

7.3 Feature Description

7.3.1 Internal Current Limit (ICL)

The internal current limit circuit is used to protect the LDO against high-load current faults or shorting events. The LDO is not designed to operate at a steady-state current limit. During a current-limit event, the LDO sources constant current. Therefore, the output voltage falls while load impedance decreases. Note also that when a current limit occurs while the resulting output voltage is low, excessive power is dissipated across the LDO, which results in a thermal shutdown of the output.

7.3.2 Enable (EN) And Under-Voltage Lockout (UVLO)

The TPS7A470x only turns on when both EN and UVLO are above the respective voltage thresholds. The UVLO circuit monitors input voltage (VI) to prevent device turn-on before VI rises above the lockout voltage. The UVLO circuit also causes a shutdown when VI falls below lockout. The EN signal allows independent logic-level turn-on and shutdown of the LDO when the input voltage is present. EN can be connected directly to VI if independent turn-on is not needed.

7.3.3 Soft-Start And Inrush Current

Soft-start refers to the ramp-up characteristic of the output voltage during LDO turn-on after EN and UVLO have achieved threshold voltage. The noise reduction capacitor serves a dual purpose of both governing output noise reduction and programming the soft-start ramp during turn-on.

Inrush current is defined as the current through the LDO from IN to OUT during the time of the turn-on ramp up. Inrush current then consists primarily of the sum of load and charge current to the output capacitor. Inrush current can be estimated by Equation 1:

Equation 1. q_iout-t_bvs204.gif

where

    7.4 Device Functional Modes

    The TPS7A470x has the following functional modes:

    1. Enabled: When EN goes above V+EN(HI), the device is enabled.
    2. Disabled: When EN goes below V+EN(LO), the device is disabled. During this time, OUT is high impedance, and the current into IN does not exceed I(SHDN).

    7.5 Programming

    7.5.1 ANY-OUT Programmable Output Voltage

    Both devices can be used in ANY-OUT mode. For ANY-OUT operation, the TPS7A4700 and TPS7A4701 do not use external resistors to set the output voltage, but use device pins 4, 5, 6, 8, 9, 10, 11, and 12 to program the regulated output voltage. Each pin is either connected to ground (active) or is left open (floating). The ANY-OUT programming is set by Equation 2 as the sum of the internal reference voltage (V(REF) = 1.4 V) plus the accumulated sum of the respective voltages assigned to each active pin; that is, 100 mV (pin 12), 200 mV (pin 11), 400 mV (pin 10), 800 mV (pin 9), 1.6 V (pin 8), 3.2 V (pin 6), 6.4 V (pin 5), or 6.4 V (pin 4). Table 1 summarizes these voltage values associated with each active pin setting for reference. By leaving all program pins open, or floating, the output is thereby programmed to the minimum possible output voltage equal to V(REF).

    Equation 2. q_vout_anyout_bvs204.gif

    Table 1. ANY-OUT Programmable Output Voltage

    ANY-OUT PROGRAM PINS (Active Low) ADDITIVE OUTPUT VOLTAGE LEVEL
    Pin 4 (6P4V2) 6.4 V
    Pin 5 (6P4V1) 6.4 V
    Pin 6 (3P2) 3.2 V
    Pin 8 (1P6) 1.6 V
    Pin 9 (0P8) 800 mV
    Pin 10 (0P4) 400 mV
    Pin 11 (0P2) 200 mV
    Pin 12 (0P1) 100 mV

    Table 2 shows a list of the most common output voltages and the corresponding pin settings. The voltage setting pins have a binary weight; therefore, the output voltage can be programmed to any value from 1.4 V to 20.5 V in 100-mV steps.

    Table 2. Common Output Voltages and Corresponding Pin Settings

    VO (V) PIN NAMES AND VOLTAGE PER PIN
    0P1V
    100 mV    		 0P2V
    200 mV    		 0P4V
    400 mV    		 0P8V
    800 mV    		 1P6V
    1.6 V    		 3P2V
    3.2 V    		 6P4V1
    6.4 V    		 6P4V2
    6.4 V
    1.4 Open Open Open Open Open Open Open Open
    1.5 GND Open Open Open Open Open Open Open
    1.8 Open Open GND Open Open Open Open Open
    2.5 GND GND Open GND Open Open Open Open
    3 Open Open Open Open GND Open Open Open
    3.3 GND GND Open Open GND Open Open Open
    4.5 GND GND GND GND GND Open Open Open
    5 Open Open GND Open Open GND Open Open
    10 Open GND GND Open GND Open GND Open
    12 Open GND Open GND Open GND GND Open
    15 Open Open Open GND Open Open GND GND
    18 Open GND GND Open Open GND GND GND
    20.5 GND GND GND GND GND GND GND GND

    7.5.2 Adjustable Operation (TPS7A4701 Only)

    The TPS7A4701 has an output voltage range of 1.4 V to 34 V. For adjustable operation, set the nominal output voltage of the device using two external resistors, as shown in Figure 23.

    ai_adj_op_bvs204.gifFigure 23. Adjustable Operation for Maximum AC Performance

    R1 and R2 can be calculated for any output voltage within the operational range. The current through feedback resistor R2 must be at least 5 µA to ensure stability. Additionally, the current into the FB pin (I(FB), typically 350 nA) creates an additional output voltage offset that depends on the resistance of R1. For high-accuracy applications, select R2 such that the current through R2 is at least 35 µA to minimize any effects of I(FB) variation on the output voltage; 10 kΩ is recommended. R1 can be calculated using Equation 3.

    Equation 3. q_r1_bvs204.gif

    where

    • VREF = 1.4 V
    • IFB = 350 nA

    Use 0.1% tolerance resistors to minimize the effects of resistor inaccuracy on the output voltage.

    Table 3 shows the resistor combinations to achieve some standard rail voltages with commercially-available 1% tolerance resistors. The resulting output voltages yield a nominal error of < 0.5%.

    Table 3. Suggested Resistors for Common Voltage Rails

    VOUT R1, Calculated R1, Closest 1% Value R2
    1.4 V 0 Ω 0 Ω ∞
    1.8 V 2.782 kΩ 2.8 kΩ 9.76 kΩ
    3.3 V 13.213 kΩ 13.3 kΩ 9.76 kΩ
    5 V 25.650 kΩ 25.5 kΩ 10 kΩ
    12 V 77.032 kΩ 76.8 kΩ 10.2 kΩ
    15 V 101.733 kΩ 102 kΩ 10.5 kΩ
    18 V 118.276 kΩ 118 kΩ 10 kΩ
    24 V 164.238 kΩ 165 kΩ 10.2 kΩ

    To achieve higher nominal accuracy, two resistors can be used in the place of R1. Select the two resistor values such that the sum results in a value as close as possible to the calculated R1 value.

    There are several alternative ways to set the output voltage. The program pins can be pulled low using external general-purpose input/output pins (GPIOs), or can be hardwired by the given layout of the printed circuit board (PCB) to set the ANY-OUT voltage. The TPS7A4701 evaluation module (EVM), available for purchase from the TI eStore, allows the output voltage to be programmed using jumpers.