5.3
Power sequencing and soft start
The individual output rails are power sequenced to reduce the inrush current during power-up. The device uses
a passive power sequencing method where it enables the individual rails when the preceding rail is within its
total operating band, that is between the respective undervoltage and overvoltage fault thresholds.
Sequence of the output rails:
•
Buck1
•
Buck2, Boost1
•
(VM1), (VM2)
Power sequencing is active any time a power rail is enabled or disabled, for example at the transition to ACTIVE.
If the device detects via the automatic use detection that a rail is not active, then power sequencing skips this
rail and proceeds with the subsequent rail.
The following conditions must be fulfilled for the power sequence to proceed with the next stage:
•
The output voltage on the individual rails must be above the undervoltage threshold
•
The rise time must be completed before the next stage is reached
For example, during ramp-up of Buck1 the device waits until its output voltage exceeds the undervoltage
threshold and until the rise time
t
Buck1
has elapsed before it initiates the ramping of Buck2 and Boost1. Under
normal operating conditions the output voltage on Buck1, Buck2 and Boost1 cross their respective
undervoltage thresholds before the rise time has elapsed.
As soon as the device enables a rail, it also enables the corresponding undervoltage monitoring. However, the
device only indicates an undervoltage event once, when the voltage rail crosses the undervoltage threshold for
the first time. The short-to-ground detection is active and the device uses it as a timeout function for the power
sequencing process. If a voltage rail is not valid within the short-to-ground detection time, then the device
indicates a fault event. Depending on the configured response to the short-to-ground event (see
device may either move into a different state or continue operation and power sequencing.
OPTIREG
™
PMIC TLF30681QVS01
Power management IC
Central functions
Datasheet
38
Rev. 1.0
2020-04-08
