I am using ld1117v33 with Vin as 4.97v and trying to get Vout as 3.3v. I am actually getting this Vout without using any capacitors or resistors. The datasheet has suggested to use two capacitors, 0.1uf for input and 10uf for output along with a 120 ohm load resistor.
When I follow the circuit, I am getting Vout as 3.27v.
I can understand the usage of capacitors but not sure about the resistor used here. Could someone tell that if there is any advantage of using the resistor here? When I remove the resistor and leave the capacitors, it does go back to 3.3V.
Best Answer
The 120 ohm resistor is only required for the 1.2V version of the LD1117 to maintain minimum regulation, with a 10 mA minimum load. It's unneeded for the 3.3V version.
That said, 3.27V is within the specs for the 3.3V version. See the VO spec on the datasheet, for the 3.3V version. The datasheet has a spec section for multiple output voltages.
That said, a 120 ohm resistor is only a 27 mA load at 3.3V. Try a larger load like 250mA and check to see if the voltage is still within range. Make sure your capacitors are as close to the LDO as possible. You may need a larger input capacitor depending on how far away your power supply is. If it's not within range at a higher load up to 800 mA it may be bad. And this is for the ST branded LD1117, other brands may have different requirements or specs.