Texas Instruments TPS54980EVM-022, User Manual

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Power Up and Down
2-9 Test Setup and Results
2.9 Power Up and Down
The TPS54980 regulator provides different modes for power up and power
down sequencing of the core and I/O voltages. By selecting different ratios for
the resistor divider R6/R7 (see Figure 4−1), the slope of the core voltage during
power up and down can be set equal to, higher than, or lower than the slope
of the I/O voltage. If the resistors R6 = R1 and R7 = R2, then the core voltage
tracks the I/O voltage. The start up voltage waveform of the
TPS54980EVM-022 for this condition is shown in Figure 2−11. The waveform
shows that the core voltage regulator tracks the output of the I/O regulator until
the core regulator reaches its nominal 1.8-V level. After that, the core regulator
starts to regulate its output at the preset 1.8-V level. The I/O regulator
continues its ramp up until the voltage reaches the nominal 3.3-V level. The
output voltage waveforms during power up do not depend on load currents.
The output voltage waveforms are powered up by asserting the ENABLE
signal while the input voltage is already applied.
Figure 2−11.
Power Up with Tracking
VO I/O 500 mV/div
t − Time − 500
µ
s/div
VO Core 500 mV/div
The power down waveform is shown in Figure 2−12. During power down, the
output voltage fall time is defined by the output capacitance and load
resistance. In this case the I/O output load resistance has been set to 20
Ω
and
the core output load resistance set to 1
Ω
. With the I/O output voltage falling
with a slew rate of about 1.25 V/ms, there is essentially no difference between
the core voltage and I/O voltage.