Hello TI,
I'm trying to continue here the thread on the min requirement for the lower feedback resistor R2 (160Kohms).
(unlike the original asker, I'm concerned about the noise and want to follow this recommendation).
when trying to achieve relatively high output voltage e.g. 5V, the implied upper resistor R1 minimal value is calculated to be ~850KOhms:
Vout = 0.793 * (1+850/160) ~ 5.0V
When i'm conducting a worst case circuit analysis and trying to calculate the maximal output voltage, i must take into
account also the Ifb (current into the feedback pin)
which can be up to 1uA according to the datasheet (with nominal value of 0.02uA ???):
As far is it can be seen, to the output voltage i need to add also the voltage built on R1 due to this Ifb current:
1uA * 850Kojms = 0.85V
i.e. i assume that Vout = Vref *(1 + (R1/R2)) + Ifb*R1 ~ 5.85V
(this before starting to include also the tolerances of Vfb, R1, R2).
This is a high, probably unacceptable, Vout max in many of the use cases.
Please advise, is there anything wrong with my assumptions, or is this the reality with this device, I need to choose between low noise or reasonable Vout max.
thanks a lot,
amotz
