I want to use the DMOS low-Dropout regulator REG102 3V3, but in the datahseet REG102 of the regulator i found two configuratons. The first configuration is without resistors divider and by connecting a capacitor on the output. The second configuration is with voltage divider,in this configuration the voltage Vout is depending on the values of the resistors and voltage Vref as is shown in the figure below:
My question is :
How the voltage Vin influence the voltage Vout in case of use of the voltage divider ?
Electronic – low dropout regulator output voltage
analogldovoltage-regulator
Related Solutions
It looks to me like a netlist/layout error:
If you are placing your fixed resistor on the dig pot footprint, it would also be messed up. Looks like you accidentally wired the CO+ and NO2- together and the NO2+ and CO- together so the LDO(Vout-Vadj) is not across a resistance as you believe.
I suggest you do not use a 3.3V zener diode as a reference- you'll get horrible line regulation (and ripple rejection), especially with a resistor as the current source, as well as bad temperature stability.
At least use a TL431 (almost as cheap as a zener in volume) which (if you give it >1mA) will maintain a very steady voltage (nominally 2.495V) and has quite reasonable temperature stability. Your 1uF in parallel should result in unconditional stability.
An LM358 should work okay with a sufficiently low pullup resistor to allow the output to get close to the positive rail so the MOSFET can turn off. The LM358 is good for 32V, your MOSFET gate is probably not rated for 32V so that limits your maximum input unless you improve your circuit.
You've not made any attempt to deal with (frequency) compensation. At some point (probably very soon) you will find out why LDOs have problems in this area when it turns into an oscillator. You may not easily see the oscillation at the output because of the huge capacitor, so look at the op-amp output to see if the circuit is stable.
Anyway: How to test
Line and load regulation test for the rated input range with different loads (minimum to maximum and a few inbetween). Measure the output voltage for each.
Temperature stability- repeat tests at different temperatures from minimum to maximum.
Stability- change the load from maximum to minimum with different input voltages and observe the output behavior-looking for droop or overshoot when the load is increased or decreased suddenly.
Ripple rejection- apply some ripple on the input at the desired frequency and observe how much gets through to the output.
Drop-out- observe the output behavior as the input is increased from zero to a voltage a few volts above the output, with various loads.
You can measure quiescent current Iq as well, if you like. If you pullup resistor is very low (like 1K) you may see a significant increase in current as the op-amp rails for a high set output voltage and input slightly too low to regulate.
Best Answer
It's described on the datasheet here:
For Vout, use the voltage from the table you've quoted (which depends on the resistors).
As you can see, the output voltage changes only slightly with input voltage until you closely (say within 0.25V or so, depending on output current) approach the dropout voltage. For voltages less than the dropout voltage it will tend to follow the input voltage down. No information is given as to what happens at very low input voltages.