I'm a long time lurker 🙂
How do I tell what is the maximum voltage drop an LDO can handle?
My mentor explained adjustable LDOs like this to me (paraphrased of course):
"An LDO is essentially a high precision, low range, voltage controller
that requires a slightly higher input voltage to function. For
example, even though an LDO is rated at (1.24-26)V if the input is
25V, it will only be able to output (24.2-24.8)V."
How can I find these boundaries in a datasheet?
Considered components:
- MIC29150/29300/29500/29750 High-Current Low-Dropout Regulators
- LT3015 Series – 1.5A, Low Noise, Negative Linear Regulator with Precision Current Limit
Sorry if my English is not good. C++ is my native language.
Best Answer
LDO means low-dropout regulator. This is understood to be a type of linear regulator. The minimum difference between input and output is called the dropout voltage. So an LDO deserves the name only if its dropout voltage is "low." Many old LDO's don't really deserve to call themselves an LDO by today's standards.
Anyway, that is not what you asked about. There are normally two constraints on the maximum input voltage. One is that there is simply a maximum recommended operating voltage. If you go above that, you may wind up with problems. Second is determined by heat dissipation. The power dissipated by a linear regulator is (Vin - Vout) * Iload. So what you normally do is figure out your maximum input voltage and maximum load current and use those to calculate the dissipation.
Then you have to check the thermal resistance of the component to figure out whether dissipating that amount of heat will cause the silicon to get too hot. I am sure you can find detailed instructions about thermal calculations on the WWW or in the search box for this forum.
In general, you will dissipate less power with lower Vin and lower load current.