LDO (TC1071) misbehaving

[bryce1]

I cant for the life of me get the voltage I want out of the TC1071. I am sure I misunderstand something in the datasheet.
The voltage divider in my case is 750k(R1) / 470k(R2), which should result in 3.1V?
Instead, I see 4.1V.
What is happening???

http://ww1.microchip.com/downloads/en/DeviceDoc/21353E.pdf


PS: I am using 1uF ceramics on the input and output. The ouput cap has a 0.5 resistor in series to account for the low esr.

[tron9000]

I take it its as drawn on page one of PDF. have you actually mounted it on a PCB or bodged it onto a strip board?

[bryce1]

I have it on a pcb

[mikerj]

What are you using for the output decoupling cap?  Does it meet the ESR requirements of this LDO?

[tron9000]

says its ceramic but From reading the datasheet it doesn't specify not using a ceramic cap, but does say an alu electro or tant can be used. Just for clarity have you tried it without your 0R5 resistor mod in?

[Odysseus]

Verify that the ADJ pin is ~1.2V.  You can also try shorting ADJ to the output and see if that gives you 1.2V.  Your cap and resistor should be sufficient. What is Vin and your load?

[PSR B1257]

750k(R1) / 470k(R2)

Nominal value or actually measured?
What type of resistor?

A picture of your PCB might help 

[wraper]

Where you bought it? Check if the marking matches the datasheet - BBNN

[bryce1]

I bought it on digikey, it is the right part.

Vin is about 4.6V. Load varies, not more than 10mA.

750k(R1) / 470k(R2)

Nominal value or actually measured?
What type of resistor?

Measured. I tried different 0603 resistors and one through hole.

[PSR B1257]

Just for curiosity, have you verified your measurement with a different meter?

Perhaps you have damaged the chip due to excess heat during soldering. Do you have a spare chip?

[bryce1]

I tried three different ones.

[PSR B1257]

Meters or chips?

[tron9000]

If we had some photies of the PCB, then this would help, might be able to spot something?

[bryce1]

You where right to insist on this, the problem lies elsewhere in the circuit. When I test the LDO config in an isolated manner, everything works just fine.

[matkar]

How much current does the circuit draw? If it doesn't go over specs try to increase regulator's output capacitor. I bet you use a 0603 1uF low voltage ceramic  one. Use at least 10uF ceramic or better yet replace it with a tantal. And remove the 0R5 resistor. Next time stick to the datasheet recomendations.