LDO (TC1071) misbehaving - Page 1
Forum section: electronics / beginners

author: bryce1
author_rank: Regular Contributor
timestamp: May 29, 2015, 10:58:02 am
content: 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.pdfPS: 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.

author: tron9000
author_rank: Frequent Contributor
timestamp: May 29, 2015, 12:05:32 pm
content: 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?

author: bryce1
author_rank: Regular Contributor
timestamp: May 29, 2015, 12:16:34 pm
content: I have it on a pcb

author: mikerj
author_rank: Super Contributor
timestamp: May 29, 2015, 12:51:02 pm
content: What are you using for the output decoupling cap? Does it meet the ESR requirements of this LDO?

author: tron9000
author_rank: Frequent Contributor
timestamp: May 29, 2015, 02:34:45 pm
content: 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?

author: Odysseus
author_rank: Regular Contributor
timestamp: May 29, 2015, 03:00:59 pm
content: 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?

author: PSR B1257
author_rank: Frequent Contributor
timestamp: May 29, 2015, 03:14:17 pm
content: QuoteNominal value or actually measured?What type of resistor?A picture of your PCB might help

author: wraper
author_rank: Unknown
timestamp: May 29, 2015, 04:03:43 pm
content: Where you bought it? Check if the marking matches the datasheet -BBNN

author: bryce1
author_rank: Regular Contributor
timestamp: June 01, 2015, 01:20:27 am
content: I bought it on digikey, it is the right part.Vin is about 4.6V. Load varies, not more than 10mA.Quote from: PSR B1257 on May 29, 2015, 03:14:17 pmMeasured. I tried different 0603 resistors and one through hole.

author: PSR B1257
author_rank: Frequent Contributor
timestamp: June 01, 2015, 02:57:56 pm
content: 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?

author: bryce1
author_rank: Regular Contributor
timestamp: June 02, 2015, 02:57:56 am
content: I tried three different ones.

author: PSR B1257
author_rank: Frequent Contributor
timestamp: June 02, 2015, 04:17:41 am
content: Meters or chips?

author: tron9000
author_rank: Frequent Contributor
timestamp: June 02, 2015, 08:23:14 am
content: If we had some photies of the PCB, then this would help, might be able to spot something?

author: bryce1
author_rank: Regular Contributor
timestamp: June 06, 2015, 05:51:41 am
content: 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.

author: matkar
author_rank: Regular Contributor
timestamp: June 06, 2015, 09:39:52 am
content: 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.