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3.8 Start-up and Shutdown with EN
Figure 3-26 and Figure 3-27 show the start-up and shutdown waveforms for U2 with EN. In Figure 3-26 , the
input voltage is initially applied and the output is inhibited by pulling EN to GND using an external function
generator. When the EN voltage is increased above the enable-threshold voltage, the start-up sequence begins
and the output voltage ramps up to the externally set value. In
Figure 3-27 , the external function generator pulls
EN to ground and the TPS543620 shuts down.
Figure 3-28 shows EN start-up with a 0.2-Ω resistor load. Figure 3-29 shows the BP5 internal LDO start-up
relative to the EN pin.
A shunt on the ENOFF_U1 jumper or RDIV_VIN can be used to test the EN start-up of U1 and U2, respectively.
When the shunt is removed from ENOFF_U1, EN is released and the start-up sequence begins for U1. When
the shunt is placed on RDIV_VIN, EN is pulled to the input voltage through the resistor divider and the start-up
sequence begins for U2.
Time (400 µs/div)
VOUT (500 mV/div)
SW (10 V/div)
EN (2 V/div)
PGOOD (5 V/div)
Figure 3-26. U2 Start-up with EN – No Load
Time (400 µs/div)
VOUT (500 mV/div)
SW (10 V/div)
EN (2 V/div)
PGOOD (5 V/div)
Figure 3-27. U2 Shutdown with EN – No Load
Time (400 µs/div)
VOUT (500 mV/div)
IOUT (5 A/div)
EN (2 V/div)
PGOOD (5 V/div)
Figure 3-28. U2 Start-up with EN – 0.2-Ω Load
Time (400 µs/div)
VOUT (500 mV/div)
BP5 (5 V/div)
EN (2 V/div)
PGOOD (5 V/div)
Figure 3-29. U2 Startup with EN – No Load and
Measuring BP5
Test Setup and Results www.ti.com
20 TPS543620 SWIFT™ Step-Down Converter Evaluation Module User's Guide SLVUBQ1A – AUGUST 2020 – REVISED MAY 2021
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