I'm designing a simple Atmel ATtiny microcontroller circuit for use in an older car. Power consumption is just microamps when idle (this is important because the circuit is powered permanently) up to a couple of tens of milliamps for short moments when active.
For the voltage regulator I chose the LM2936-5.0 (
datasheet). This is an automotive LDO which provides protection against the hostile 12V system, has a very low quiescent current and is well available (even from hobby-oriented stores like Conrad which may be important if someone wants to build the circuit for themselves).
I want to squeeze the circuit in an existing module which puts some constraints on the design: The module is mounted in the engine bay which means a temperature range from freezing cold in winter to almost cooking in summer and the components may not be taller than 4 mm because the board will reside in a narrow space behind the existing PCB.
This is not an issue for the (SMD) voltage regulator, microcontroller, transistors and passives, but the LM2936-5.0 requires an output capacitor of at least 10µF and I don't think I can squeeze an electrolytic can in there. Besides, given the temperature conditions I'm not sure an electrolytic capacitor is the best choice for this to begin with.
Right now I'm using a 10µF / 16V tantalum capacitor. Works fine in my prototype. Great temperature stability and it should be well derated for the entire temperature range (LDO output voltage is 5V). Since the circuit is permanently powered I don't think the inrush current is much of an issue.
But... judging by capacitor topics on this forum and elsewhere, using tantalum capacitors is almost considered a crime nowadays. According to some it's just a matter of time before they explode.
That's exaggerated of course but still I'm a bit worried about my choice. Especially if others decide to build the circuit for their car.
I was wondering what others think about this.
- A) 10µF / 16V tantalum capacitors are fine. Just make sure to use a reputable brand
- B) I'd rather go with tantalum polymer (10µF / 10V or perhaps even just 6.3V). Due to the lower ESR a series resistor is mandatory in combination with the LM2936
- C) Avoid tantalum like the plague. Go with X7R MLCC and a series resistor (what value would you suggest considering the poor stability of these capacitors in comparison to tantalum ones?)
- D) Forget about the LM2936 and use another LDO that is designed to work with pretty much any MLCC/ESR (suggestions on something that is targeted at automotive applications, outputs up to around 50mA, has very low quiescent current, comes in a hand-solderable package and is widely available in low quantities?)
Just to be clear: I'm not interested in mass production or cost optimization. This is just hobby-level stuff but obviously I don't want it to fail prematurely. I want it to last for many years.