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3.4 Load Transient and Loop Response
Figure 3-10 and Figure 3-11 show the response to load transients for both designs. The current step is from 1.5
A to 4.5 A and the current step slew rate is 1 A/µs. An electronic load is used to provide a DC 1.5-A load and the
load transient circuit on the EVM is used to provide a 3-A step. The VOUT voltage is measured using TP10 for
U1 and TP29 for U2.
When using the load transient circuit included on the TPS543620EVM, slowly increase amplitude of function
generator for desired load step amplitude then vary the rise and fall times for the desired slew rate. The current
for the load step can be sensed with the ISNS test point. The default resistors on the EVM provide a gain of 20
A/V. With this gain, a 3-A step will result in 150-mV at the ISNS test point.
Note
To use the load transient circuit with U1, move R27 to R28.
Figure 3-12 and Figure 3-13 show the loop characteristics for both designs. Gain and phase plots are shown for
V
IN
voltage of 12 V and a 0.2-Ω resistive load.
Time (40 µs/div)
IOUT (1 A/div)
VOUT AC (20 mV/div)
Figure 3-10. U1 Transient Response
Time (100 µs/div)
VOUT AC (20 mV/div)
IOUT (1 A/div)
Figure 3-11. U2 Transient Response
Frequency (Hz)
G
ai
n (
dB
)
P
hase (
°)
100 200 500 1000 10000 100000 1000000
-40 -120
-20 -60
0 0
20 60
40 120
60 180
Gain
Phase
Figure 3-12. U1 Bode Plot
Frequency (Hz)
G
ai
n (
dB
)
P
hase (
°)
100 200 500 1000 10000 100000 1000000
-40 -120
-20 -60
0 0
20 60
40 120
60 180
Gain
Phase
Figure 3-13. U2 Bode Plot
www.ti.com Test Setup and Results
SLVUBQ1A – AUGUST 2020 – REVISED MAY 2021
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