LT8645S-2 BST

Hello,

the Voltage at BST pin will 'switch' between INTVCC and VSW+INTVCC along with the switching frequency. You can easily check its behaviour by a LTSpice simulation to see how this 'Boost' circuitry works:

This takes care to achieve a drive voltage which is 'INTVCC' value higher than the input voltage.

Hi Markus,

Thanks for the clarifications. So what will be the voltage on CBST? What voltage rating is required for CBST? 

Hello,

when designing the circuitry you should be aware of the general function of this part und a buck regulator, which seems to be 'questionable' here. So here is my explanation:

If top FET is conducting Vswitch will see approx Vin. Hence Vbst will see Vin+Vintvcc. So if you know your maximum Vin you can calculate maximum Vbst easily.