Hello,
For the TPS746 LDO, I need to know the recommended values for the R1/R2 resistors to be connected to the VFB pin.
If the max value is in the 10K range then that too low for my application.
On the older LP5922 device, the maximum resistor value is around 100K. However, the part is not recommended for new designs (NRND).
Also, the LP38502 device has a maximum resistor value of 10K, which is too low.
Regards,
Tony
Hi Tony,
For the TPS746, the upper limit for the feedback resistors is set by the feedback pin current. To ensure Equation (2) of the datasheet is accurate, the feedback pin current should be negligible compared to the resistor string current. A good rule of thumb is to make the resistor string current 100 times larger.
Vfb / R2 >= 100 * Ifb,max
R2 <= Vfb / (100 * Ifb,max) = 0.55 / (100 * 0.1 uA) = 55 kOhms
R1 can then be chosen using Equation (2) and the output voltage for your application:
If your application requires larger feedback resistors, you may need to account for the feedback pin current when calculating your desired output voltage:
Vout = Vref * (R1/R2 + 1) + Ifb * R1
Thanks,
Gerard
