I am building a small circuit with an extra SRAM, for the arduino.
I am using two 23k256 and a TXB0108 logic level shifter. I am thinking of powering the chips simply by voltage divider from 5 volts, the whole circuit is using.
I wonder how much current should I leave for the chips?
I went through data sheets of both chips, and all I could find that 23k256 needs 1mA and TXB0108, barelly uses any current - 1uA. So in total I understand I need 3mA, but should I leave a bit more? as using standart 330/680 resistors I could supply 10mA, or would it be way to much and would fry the chips.
Any comments welcome.
do you know any voltage regulators, which could output 5V and 3V3 from one chip? I could not find any and I am trying to save space on PCB, so though of using the voltage divider.
i know, that you can't use voltage divider for low impendance circuit, because the current will just go to ground throught the circuit.
but is this the case? (just for learning purposes)
I am thinking of powering the chips simply by voltage divider from 5 volts,
A few possibilities:
See if you can power the chip at 5v. They may have maximum Vcc at 5v. Or they may be able to operate at 5v - you will need to see if you can take the changes.
If you have to power it at a lower voltage, see if you can drop the 5v easier. Two silicon diodes in serial, plus a resistor to ground will provide about 1.4v drop; or a resistor to an LED (white LEDs for example are around 3v). or a zener.
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I've used a simple RED LED in cases like this. It will reduce 5V to something a 3.3V chip will be happy with. I also use a 680 ohm resistor to ensure the LED lights up. That way I get my pilot light (power on) too.
BillO:
I've used a simple RED LED in cases like this. It will reduce 5V to something a 3.3V chip will be happy with. I also use a 680 ohm resistor to ensure the LED lights up. That way I get my pilot light (power on) too.
Nice bit of thinking outside the box, provided you don't overload the LED by pulling too much current through it.
BillO:
I've used a simple RED LED in cases like this. It will reduce 5V to something a 3.3V chip will be happy with. I also use a 680 ohm resistor to ensure the LED lights up. That way I get my pilot light (power on) too.
thats a very good tip. thank you.
saved me some space on tiny pcb and three components less (no v regulator circuit + led works as power on indicator)