SBVU078 November   2022

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Setup
    1. 2.1 LDO Input/Output Connector Descriptions
      1. 2.1.1 VIN and GND
      2. 2.1.2 BIAS and GND
      3. 2.1.3 VOUT and GND
      4. 2.1.4 EN
    2. 2.2 Optional Load Transient Input/Output Connector Descriptions
      1. 2.2.1 VDD and GND
      2. 2.2.2 J16
      3. 2.2.3 J18
      4. 2.2.4 J21
      5. 2.2.5 J22
      6. 2.2.6 J23
      7. 2.2.7 J24
    3. 2.3 TPS7A53A-Q1 LDO Operation and Component Selection
    4. 2.4 Optional Load Transient Circuit Operation
  5. 3Board Layout
  6. 4TPS7A53EVM-080 Schematic
  7. 5Bill of Materials

2.4 Optional Load Transient Circuit Operation

The TPS7A53EVM-080 evaluation module contains an optional high-performance load transient circuit to allow efficient testing of the TPS7A53A-Q1 LDO load transient performance. To use the optional load transient circuit, install the correct components in accordance with the application. Modify the input and output capacitance connected to the TPS7A53A-Q1 LDO to match the expected operating conditions. Determine the desired peak current to test, and modify the parallel resistor combination of R8, R9, R10, R11, and R12 as shown:

Equation 1. IPeak=VOUTR8R9R10R11R12

The slew rate of the load step can be adjusted by C16, R13, R14, and R16. In this section, only R14 and R16 are adjusted to set the slew rate. For a 1-mA to 3-A to 1-mA load step, use Table 2-1 to select a value of R14 and R16 that results in the desired rise or fall time.

Table 2-1 Suggested Ramp Rate Resistor Values
R14R16Rise, Fall Time
90.9 kΩ97.6 kΩ20 µs
44.2 kΩ47.5 kΩ6 µs
28 kΩ23.2 kΩ3.3 µs
6.65 kΩ5.9 kΩ950 ns

After the EVM is modified (if needed), connect a power supply to banana connectors J24 (VDD) and J30 (GND) with a 5-V DC supply and a 1-A DC current limit. As shown in Figure 2-3 and Figure 2-4, the TPS7A53A-Q1 transient response is very fast and the output voltage recovers in well under 1 ms after the initial load transient. Use a pulse-duration limit of 1 ms to prevent excessive heating of the pulsed resistors (R8, R9, R10, R11, and R12). Configure a function generator for the 50-Ω output, in a 0-V DC to 5-V DC square pulse. If necessary, burst mode can be configured in the function generator for repetitive, low duty cycle, load transient testing.

A 20-kΩ resistor is installed on the EVM at R14, and a 20-kΩ resistor is installed on the EVM at R16. These resistors provide approximately 1-A/μs slew rate from 1-mA to 3-A, and 1-A/μs slew rate from 3-A to 1-mA. Figure 2-3 and Figure 2-4 provide example test data with R14 = 20 kΩ and R16 = 20 kΩ. The the red trace is the output voltage and the green trace is the output current. R8, R9, R10, R11, and R12 provide 3-A of pulsed load. The resulting test data shows a 1-mA to 3-A load step on VOUT of the LDO, with only a 47-μF capacitor on the output of the LDO.

GUID-20220913-SS0I-9213-WGRT-SVNGHCZMHLNC-low.jpgFigure 2-3 TPS7A53EVM-080 Load Transient Results: 1-mA to 3-A Load Step
GUID-20220913-SS0I-LNGX-H1W7-3SPGHH0XDSKR-low.jpgFigure 2-4 TPS7A53EVM-080 Load Transient Results: 3-A to 1-mA Load Step