TPS62140 Regulation Near 100% Duty Cycle

Q: TPS62140 Regulation Near 100% Duty Cycle by 1397334

The datasheet describes that the TPS62140 can operate with a 100% duty cycle by passing the input continuosly through the hi-side FET.  However, what is the expected behavior when the TPS62140 is approaching the 100% duty cycle and how does this affect the output tolerance/regulation?  As an example, my customer has a 5V rail with a specified tolerance (5%) which is supplied by a battery that has a range of 5V-9.5V.  When the battery droops close to 5V the output will the output still regulate correctly or will the switch opens at a duty cycle less than 100% passing a higher voltage? If so what is the duty cycle will the TPS62140 continuously engage the hi-side FET?

A: Re: TPS62140 Regulation Near 100% Duty Cycle by 1090425.

The information you need can be found on pages 3 and 16 of the datasheet.  This IC is a standard buck converter and as such cannot increase the input voltage.  So, on page 3, the Vout range is given with the condition that Vin > Vout.

There is more detail in the 100% mode section on page 16 of the datasheet.  As long as Vout remains below where it should be, the high side FET turns on.  When Vin is very low, near Vout, it remains on for 100% of the time.  It can maintain being on 100% of the time indefinitely.  Now, there are simply IR drops from Vin to Vout.  Equation 3 computes the minimum input voltage that can maintain a desired output voltage at a certain load current.  Your customer can compute this equation based on their system needs.

If the 5V output will not maintain regulation under their operating conditions, then I suggest the TPS63060 buck-boost converter.  It can buck or boost the input voltage to keep the output regulated.