Datasheet

Time = 20 s/divm
200 mA/div
2 V/div
20 mV/div
C3: V ac coupled
OUT
C1: SW
C4: I
L
No Load
EN Floating
C3
C4
V = 5.5 V
V = 5 V
IN
OUT
Time = 40 s/divm
2 V/div
V
IN
I = 1 A
EN Floating
OUT
V
OUT
Time = 200 µs/div
5 V/div2 V/div2 V/div
C1: V
IN
C2: EN
C3: V
OUT
Time = 1 ms/div
5 V/div2 V/div2 V/div
C1: V
IN
C2: EN
C3: V
OUT
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2.9 Shutdown
The shutdown waveforms are shown in Figure 19 and Figure 20. The input voltage for these plots is 12 V
with a 3.5-A resistive load. The top trace shows V
IN
, the middle trace shows EN, and the bottom trace
shows V
OUT
. In Figure 19 the input voltage is removed, and when the input falls below the undervoltage
lockout threshold, the TPS54340 shuts down and the output falls to ground.
In Figure 20, the input voltage is held at 12 V, and EN is shorted to ground. When EN is grounded, the
TPS54340 is disabled, and the output voltage discharges to ground.
Figure 19. Shutdown Relative to V
IN
Figure 20. Shutdown Relative to EN
2.10 Low Dropout Operation
For improved low dropout operation, the TPS54340 includes a small integrated low-side MOSFET to pull
SW to GND when the BOOT to SW voltage drops below 2.1 V. This recharges the BOOT capacitor for
driving the high-side MOSFET. Figure 21 shows the steady state operation and Figure 22 shows the start
up and shutdown in a low dropout condition.
Figure 21. Low Dropout Operation Figure 22. Low Dropout Start Up and Shutdown
11
SLVU794A–October 2012–Revised February 2013 Using the TPS54340 Step-Down Converter Evaluation Module
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