Datasheet

Time - 500 µs/div
1 V/div
G012
200 mV /div
V /div
OUT
V /div
IN
Time - 500 µs/div
1 V/div
1 A/div
G011
200 mV /div
I , Inverted for Clarity
OUT
V /div
OUT
V /div
IN
Time - 500 µs/div
1 V/div
1 A/div
G010
200 mV /div
I , Inverted for Clarity
OUT
V /div
OUT
V /div
IN
www.ti.com Test Setup and Results
2.9 Powering Up
Figure 11 and Figure 12 show the start-up waveforms for the EVM. In Figure 11, the output voltage ramps
up as soon as the input voltage reaches the UVLO threshold as set by the R1 and R2 resistor divider
network. In Figure 12, the input voltage is initially applied and the output is inhibited by using a jumper at
JP1 to tie EN to GND. When the jumper is removed, EN is released. When the EN voltage reaches the
enable-threshold voltage, the start-up sequence begins and the output voltage ramps up to the externally
set value of 1.2 V.
Figure 11. TPS54678EVM-155 Start-Up Relative to V
IN
Figure 12. TPS54678EVM-155 Start-up Relative to Enable
The TPS54678 is designed to start up into pre-biased outputs. Figure 13 shows the output voltage start up
waveform when the output is prebiased with 550 mV.
Figure 13. TPS54678EVM-155 Start-up into Pre-bias
11
SLVU747–June 2012 TPS54678EVM-155 6-A, SWIFT™ Regulator Evaluation Module
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