Texas Instruments TPS7A13EVM-057, Руководство пользователя, Страница: 7 / 19

The slew rate of the load step can be adjusted by C11, R7, R8, and R9. In this section, only R8 and R9 are
adjusted to set the slew rate. For a 0-mA to 300-mA load step, use
Table 3-1 to select a value of R8 and R9 that
results in the desired rise or fall time.
Table 3-1. Suggested Ramp Rate Resistor Values
R8 R9 Rise/Fall Time
107 kΩ 86.6 kΩ 9.6 µs
59 kΩ 43.2 kΩ 4.8 µs
36.5 kΩ 21.5 kΩ 2.4 µs
19.1 kΩ 10.7 kΩ 1.2 µs
9.31 kΩ 5.23 kΩ 600 ns
4.53 kΩ 2.55 kΩ 300 ns
2.15 kΩ 1.24 kΩ 150 ns
402 Ω 267 Ω 30 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 3-3 and Figure 3-4 , the TPS7A13
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 2.49-kΩ resistor is installed on the EVM at R8, and a 2-kΩ resistor is installed on the EVM at R9. These
resistors provide approximately 1 A/μs slew rate from 0 mA to 300 mA.
Figure 3-3 and Figure 3-4 provide
example test data with R8 = 2.49 kΩ and R9 = 2 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 299 mA of pulsed
load. The resulting test data shows a 1-mA to 300-mA load step on VOUT of the LDO, with only a 1-μF capacitor
on the output of the LDO.
Figure 3-3. TPS7A13EVM-057 Load Transient Results: 1-mA to 300-mA Load Step
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SBVU074 – NOVEMBER 2021
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