Hi,

Those resistors may used to define a particular output voltage (by changing the divider ratio) with the given Vref. It is not always the case where we will use only one output voltage throughout, in the case of these power-management blocks.

i don't see any other issues. you have to use it.

Thanks
Anil

raja.cedt wrote on Feb 21^st, 2013, 6:10am:


So what if i have a large Cload, won't that affect my PSRR?

For the same Phase Margin, with resistive feedback the compensation cap can be much lesser, but in unity gain feedback structure compensation cap required will be much more. This might degrade the PSRR.

praveen

Advantage: the one without resistive feedback has higher loopgain.
Disadvantage: you will need an extra block if you want a vout different from vref.

Larry_80 wrote on Feb 20^th, 2013, 4:57pm:


If PSSR is a major concern, an item I have not seen mentioned is the manner in which the resistors are implemented and if they are adjustable using analog switches. Parasitic capacitance of either the resistors or the switches to the supply can significantly reduce the high frequency supply rejection. Hence, the use of the topology and substrate connections of resistors and any potential switches to adjust the resistor ratio, must be considered to optimize high frequency PSSR. It took me some time to track down this issue when it significantly reduced the PSSR of an LDO using a layout extracted view of the block when compared to its schematic view based simulation.