SBVU073A november   2021  – june 2023 TPS7A14

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 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 J13
      3. 2.2.3 J15
      4. 2.2.4 J16
      5. 2.2.5 J18
      6. 2.2.6 J19
      7. 2.2.7 J22
      8. 2.2.8 TP2, TP3, and TP4
      9. 2.2.9 TP5
    3. 2.3 TPS7A14 LDO Operation
    4. 2.4 Optional Load Transient Circuit Operation
  6. 3Board Layout
  7. 4TPS7A14EVM Schematic
  8. 5Bill of Materials
  9. 6Revision History

2.4 Optional Load Transient Circuit Operation

The TPS7A14EVM-058 and TPS7A14EVM-095 evaluation modules contains an optional high-performance load transient circuit to allow efficient testing of the TPS7A14 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 TPS7A14 LDO to match the expected operating conditions. Determine the desired peak current to test, and modify the parallel resistor combination of R2, R3, R4, R5, and R6 as shown:

Equation 1. GUID-20211005-SS0I-JVJM-NKVN-VZCF0DQ3GNJM-low.gif

The slew rate of the load step can be adjusted by C11, R7, R8, and R9. In this section, only R8 and R9 is adjusted to set the slew rate. For a 0-mA to 1-A to 0-mA load step, use Table 2-1 to select a value of R8 and R9 that results in the desired rise or fall time.

Table 2-1 Suggested Ramp Rate Resistor Values
R8 R9 Rise/Fall Time
97.6 kΩ 86.6 kΩ 10 µs
52.3 kΩ 40.2 kΩ 5 µs
31.6 kΩ 20.5 kΩ 2.5 µs
12.4 kΩ 8.06 kΩ 1 µs
6.19 kΩ 4.02 kΩ 500 ns
3.74 kΩ 2.43 kΩ 300 ns
2.49 Ω 1.62 Ω 200 ns
806 Ω 806 Ω 100 ns

After the EVM is modified (if needed), connect a power supply to banana connectors J17 (VDD) and J21 (GND) with a 5-V DC supply and a 1-A DC current limit. As illustrated in Figure 2-3 and Figure 2-6, the TPS7A14 transient response is very fast and the output voltage recovers in well under 1 ms after the initial load transient. Therefore, use a load transient pulse duration limit of 1 ms to prevent excessive heating of the pulsed resistors (R2, R3, R4, R5, and R6). 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 10.7-kΩ resistor is installed on the EVM at R8, and a 10-kΩ resistor is installed on the EVM at R9. These resistors provide approximately 1 A/μs slew rate from 0 mA to 1 A. Figure 2-3 and Figure 2-6 provide example test data with R8 = 10.7 kΩ and R9 = 10 kΩ. The red trace is the output voltage and the blue trace is the output current. J10 provides 1 mA of DC load current and R2, R3, R4, R5, and R6 provide 949 mA of pulsed load. The resulting test data shows a 1-mA to 950-mA load step on VOUT of the LDO, with only a 2.2-μF capacitor on the output of the LDO.

GUID-20211025-SS0I-KMFW-GQ03-XJV7V8G512JF-low.jpgFigure 2-3 TPS7A14EVM-058 Load Transient Results: 1-mA to 950-mA Load Step
GUID-20211025-SS0I-MVHJ-BN33-RLNGDCVQ13ZG-low.jpgFigure 2-4 TPS7A14EVM-058 Load Transient Results: 950-mA to 1-mA Load Step