hi
ive got a requirement to add a clock to a 328, so i need a battery backup for it if the power goes out just wondering what is the most common surface mount 100ma regulator i could use / most popular one. or maby is there a more suitable one that i could use for such a small current?
i did measure a single 328 running think it was about 15ma if i remember
my first choice would be a 78L05L just wondering if this is a common regulator
jonisonvespa:
hi
ive got a requirement to add a clock to a 328, so i need a battery backup for it if the power goes out just wondering what is the most common surface mount 100ma regulator i could use / most popular one. or maby is there a more suitable one that i could use for such a small current?
i did measure a single 328 running think it was about 15ma if i remember
my first choice would be a 78L05L just wondering if this is a common regulator
thank you
What are your requirements for dropout voltage, etc.?
What is powering the circuit the rest of the time? You need to design it so that there is an orderly handover of power from the PSU to the battery. The usual solution is to feed the voltage regulator from the PSU through a diode and from the battery via another diode.
No need to have battery power for the 328p just to maintain time/date information. Do what most do and add a simple I2C RTC module that has it's own battery back-up protection.
The other thing is, the 78L05L v.regs have a 5mA or so quiescent [bias] current, so not great
for low-power apps. Better choice would be something like an LP2950.
Have you tried entering your requirements on webench and checking out TI's suggestions?
Just tell 'em your voltage/current requirements and optimize for price/footprint/efficiency. Requires registering at TI I think, but it's well worth it.
I just happened to tabulate 9 TO-92 v.regs today for a project I'm working on. Here is the list
versus current spec [not exhaustive - just the datasheets I had on file, BTW].
Note - some of these parts have "unusual" pinouts. There are also a lot of smt v.regs that I
wasn't interested in here.
Thermal resistance for TO-92 is 200 degC/W, so you have to be a little careful about over
heating at the higher currents. Eg, with Pd = Vdrop * Iload = 0.5W, and you limit Vdrop to
0.5W/.25A = 2V, it'll still burn your finger.