SBVS118 August   2017 TPS7A47-Q1

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 Internal Current Limit (ICL)
      2. 7.3.2 Enable (EN) And Undervoltage 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
  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 Receiving Notification of Documentation Updates
    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

Package Options

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

7 Detailed Description

7.1 Overview

The TPS7A47-Q1 is a positive voltage (35 V), ultralow-noise (4.2 µVRMS) LDO capable of sourcing a 1-A load. The TPS7A47-Q1 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

TPS7A47-Q1 fbd_sbvs118.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 when load impedance decreases. Also, 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 Undervoltage Lockout (UVLO)

The TPS7A47-Q1 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 the 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. Use Equation 1 to estimate in-rush current:

Equation 1. TPS7A47-Q1 q_iout-t_bvs204.gif

where

  • VOUT(t) is the instantaneous output voltage of the turn-on ramp
  • dVOUT(t) / dt is the slope of the VO ramp
  • RLOAD is the resistive load impedance

7.4 Device Functional Modes

The TPS7A47-Q1 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

For ANY-OUT operation, 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. TPS7A47-Q1 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

The TPS7A47-Q1 has an output voltage range of 1.4 V to 34 V. For adjustable operation, set the nominal output voltage of the device (as shown in Figure 23) using two external resistors.

TPS7A47-Q1 ai_adj_op_sbvs118.gif Figure 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. Equation 3 calculates R1.

Equation 3. TPS7A47-Q1 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.