LTC3407A-2 uC supply problem

[onoffman]

Refer to the circuit **broken link removed**

I am using the same except r4=887k and r3= 197k for getting 3.3V
and r2=887k and r1=442k for 1.8v

Vout is given by 0.6(1+r2/r1) volts and 0.6(1+r4/r3)


I have soldered the DFN10 pack chip and after that i am using this as a source for tests

9v batt>Lm7805>"LTC3407A-2 circuit"


But I am getting 1.4Volts and 3.4v. second one seems ok but the first voltage is way too low .. i used 1% tolerance resistors .
Please help me ,what may be the reason of low output? How to test it .

 

[karesz]

Hi onoffman,
Can you check it with an oscilloscope for oscillatings/signalforms?
Are you sure, that your components are all right? What about the inductances & layout pls?
Do it work wrong too if you apply a 4.5V battery at the input & no other 5V regulator?
Are you sure, that your layout rules are all right_sorry, an oscillating/falls work modus is possible_check the "Layout rules" in datasheet...
To end: you can change both inductances from 1.8V to 3.3V & vica versa...
K.

 

[onoffman]

thank you for the help , components are all correct and layout too.

i tested as follows
> reduced the 5v supply with a 270ohm to approx 4.7v .(Measured with DMM at input )

resulted in o/p 1.01v and 2.7v

This shows that the regulator is not running...as i suspected IC is wrongly soldered.

Vref1 =0.5v
and Vref2=2v !!!!
datasheet tells these need to be 0.6v
IC is in dfn10 pack i soldered with a thin iron , it got tilted a little .. i will borrow a Hot air pencil and remove the chip and put new one properly.

>

 

[karesz]

You must check for soldered backside (thermal)pad too_if it exist, and for contacts/shorts between pins their dont have contacts...
K.

Added after 3 minutes:

You must be clear, that it dont exist some oscillating in your circuit!
You need an oscilloscope and is not every time possible to see it, than the probe has at 10pF own capacitors_a changing in circuit situation is resultat if you touch with them the component points...

Added after 3 minutes:

If you will solder a DFN IC, you need very good planarity!!_it must be less as 50uMETER!
You can only one pin/pad presolder & need good flux too befor soldering!

Added after 2 minutes:
Check pls these film, from "electronicus": Post09 Feb 2010 14:33 Re: Manual soldering of TQFP 100 pin chips, Look the video demonstration : https://www.youtube.com/watch?v=vZ1qisX52rI&feature=related