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Old 14th September 2014, 06:41 PM   #1
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Default LT1963 simple pcb

Trying to get something better than my LM317 regs that would fit on a very tight space, so before I try something like trying to squeeze the super reg or a salas in smds, I wanted to try the LT1963.

The psychological limit is 1inch x 1inch or 25mm x 25mm

Voltages required would be 5V, 8V and 10V

Here is what I got so far

Click the image to open in full size.

The part shown is a TI that gives almost identical performance in the same package.
Almost datasheet implementation, with the difference that instead of using R1, I am using a led and an LM329 for the reference.

Two leds would give ~5V.
A led and an LM329 would give ~10V.
An LM329 would give ~8V.

Does it make sense to use such a scheme like in LM317 to reduce impedance etc? And if so, would it benefit from filtering the reference?

The current setup gives a nice pcb so far

Click the image to open in full size.

Note that the reference has an isolated ground pad, in order to allow sense-grounding it close to the load.
And if the reference thingy does not work, I can always use a normal resistor with it.

The cap pads are selected for ceramics with low capacitance drop with frequency, but the big pads would also allow soldering of other types, like polymer or tantalum.

Any thoughts or suggestions?
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File Type: png brd.PNG (39.5 KB, 420 views)
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Old 16th September 2014, 08:50 AM   #2
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OK here is the final pcb as ordered.

I will test and report back any measurements

Click the image to open in full size.
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Old 22nd October 2014, 06:50 PM   #3
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I just received my pcbs and parts...

This does not work. The thing is that LT1963 gets the adjust pin at 1.21V referenced to ground which is not enough to light the leds.

This is different than the LM317 which builds its reference with reference to the output.

This means that for the LT1963, R2 has to be replaced with the led/lm329 reference, and not R1

Meh... That is what you get for being careless

The pcbs still work, but you have to replace the two leds with a resistor
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Old 22nd October 2014, 08:02 PM   #4
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Here is the newest version

Click the image to open in full size.

You can see now the led/reference between the adjust and the output.

Which also allows for a very nice sense line, just like in the non-adjustable version.

And here is how the new pcb will look

Click the image to open in full size.
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File Type: png schb.PNG (22.0 KB, 118 views)
File Type: png brdb.PNG (32.4 KB, 116 views)
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