Hi guys,
I'm using with the TPS7A4700 and I want to get Vout of 3.3v
The Vin is 3.6v , is it possible?? In the datasheet is written something with Vo(nom) that the Vin should be either greater than 3v or greater than Vo(nom) +1v. What does it mean??
In addition the input capacitor in my design is 10uF Tantalum capacitor and the output capacitors are 4 capacitors of 10uF, each of them Tantalum as well.
Aviad.
Hi Aviad,
First, your capacitor selections meet the datasheet requirements and should be fine.
Regarding your question on the input voltage - Vo(nom) + 1V is somewhat common in linear regulator datasheets.
Here, the value of "1V" is defined as the voltage "dropout" of the linear regulator.
The performance of a linear regulator gets worse as the input voltage gets very close to (Vout +V_dropout).
Some small amount of dropout is required to keep the LDO functional.
See section 8.2.2.2 for more details in the datasheet.
An additional reason to maintain at least 1V of dropout is because that is where the datasheet table values were captured.
So it is very easy to look up the expected operating conditions of the linear regulator.
If you wish to operate at 3.3V input and 3V output, you will want to limit your output current to well under the maximum for this component.
For these exact values, 500mA output current will typically be allowable as shown in the table.
For a 500mA load, only 216mV of dropout is needed (typically).
Please make sure to consider your input and output tolerances.
For example, if the input and output have 3% tolerance, you will only have 111mV worse case of dropout voltage.
(3.3V*97%) - (3V*103%) = 111mV
In this case you may want to limit your load current to 250mA to give yourself some additional tolerance.
Thanks,
- Stephen
