I am designing an application where the output voltage is variable and might approach 7V. Input is 8-9V.The only maybe relevant spec is the BOOT-PH rating, the absolute maximum ratings for the TPS54622 output voltage specifies BOOT-PH: 0 to 7.5V. Is this relevant?
The boot pin would be pumped up when PH=VIN to approx. 2*VIN-boot diode drop, so this would limit the input voltage to below 8V... unless the "boot charge" circuit does some voltage limiting.
I guess the BOOT-PH rating is independent on the output voltage, so even stepping down from 15V to 12V should work, is this correct?
Yes, stepping down from 15V to 12V will work. The BOOT-PH rating will not be of concern. As you guessed internally the boot charge circuit from VIN is a regulator for the BOOT-PH voltage that keeps this within the abs max ratings for the device.
Let me know if you have any further questions.
DC/DC Power Applications Engineer
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