Texas Instruments TPS54973EVM-017, Руководство пользователя, Страница: 26 / 34

Start Up
2-12
Figure 2−14.
Measured Start Up Waveform, Four Diode Precharge
VI 500 mV/div
t − Time − 5 ms/div
VO 500 mV/div
Figure 2−15 shows the start up waveform with the output precharged through
four diodes and no load. Compare the precharge level to that in Figure 2−14
to see how start up load current affects the voltage drop across the diodes and
the final precharge voltage. As in the previous example, when the internal
reference exceeds the voltage fed back to the VSENSE pin, the output begins
to ramp up to its final preset value at the slow start rate. It is important to note
how the precharge level in Figure 2−15 is very close to the final output value.
The precharge level must never exceed the output set point under any line or
load condition for proper circuit operation. This would be the case if less than
four diodes were used.
Figure 2−15.
Measured Start Up Waveform, Four Diode Precharge and No Load
VI 500 mV/div
t − Time − 5 ms/div
VO 500 mV/div