VDD = 3.6V okay?

[Chris]

Dear All,

I know that the max. input on VDD is 3.6V. But as a rule of thumb, I normally try to stay below the max. rating. But this time I have a peripheral LDO with 3.6V output which I could use to power VDD so I can skip VDDH and the inductor. Is it really, really okay? Like, really? :) 

Another option could be to only power VDDH and VBUS (two different supplies) - in all the reference circuits, VDD is always connected. If only powering VDDH, can VDD be left unconnected? But the inductor is still required for internal reference voltage, I guess?

[Andreas]

Hi,

 

The inductor you mention is only needed if you want the power supply to use the 'DCDC mode', it will work without it but then in 'LDO mode'. 3.6V is the upper bound of the recommended supply range, we obviously can not recommend violating the recommended operating conditions and thus the supply range the IC has been qualified for. The absolute maximum rating is 3.9V, so it might be OK (probably not really OK) for short periods on your lab bench, but you should not go to production with it.

 

I suggest you take a look at our reference design config. 2, which shows supply on VDDH without any DCDC inductors, using VDD as an optional output for external circuitry. VBUS is only needed if you plan on using the USB peripheral, this is the same regardless of the power supply configuration: connect VBUS to the 5V USB voltage and hook a 4.7µF on DECUSB.

 

Best regards,

Andreas