Which step up converter to choose for a fixed Vout independent from Vin

Guest #4451250 
Hi there,
for my project I require a step up converter to power a dc motor powered 
vacuum pump to run at 6.5 volts (this gives the best ratio of 
performance and noise level). The project will be powered by a single 
cell LiPo battery. If I understand the datasheets (e.g. TI lmr62014) of 
some of the lower cost step up converters correctly the Vout will be 
depending on Vin, so Vout will be higher when the LiPo cell is at 4.2 
than at around 3.7V. Is this correct and are there alternatives that 
keep Vout stable even if the LiPo voltage drops?
Also, can I use a step-up converter's enable/shutdown pin to switch on / 
off my DC motor or do I need to switch load with a separate transistor / 
fet after the converter is started up?

Thanks for your help!
Jens
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Guest 
All DC/DC converters (I am aware of) regulate the output voltage.  The 
LMR62014 definitely does.

As you can see in the connection diagram on page 2 of the LMR62014 data 
sheet, the output remains connected to the input via L1 and D1 even if 
the converter is in shutdown. So you will need a separate FET.
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Guest 
Hi Peter,
thanks for the swift reply and good advice! Any step up converter that 
doesn't require external diode & fet that you would recommend (<=70 cent 
/1000u)?

@Andreas: Danke für den Tip!

Gruß,
Jens
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