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Low noise symmetrical PSU TPS7A4701 and TPS7A3301
Low noise symmetrical PSU TPS7A4701 and TPS7A3301
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Old 21st April 2014, 11:04 AM   #1
mravlca is offline mravlca  Slovenia
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Default Low noise symmetrical PSU TPS7A4701 and TPS7A3301

Hi!

So I was checking web to see if there are any new LDO regulators that have low noise output, so I came across TPS7A4701 and TPS7A3301. Both regulators have approximately same specs and are capable of giving 1A output, input voltage is up to +/-36V and maximum output voltage is +/- 33V, which is ideal for preamplifiers, DACs, headphone amps and similar devices. I designed eagle library and PCB which is now in size 66.5mm x 36.3mm. I would like to know what do you think about PCB layout and I would like to know how much should those pads on QFN package need to look out of it to make good solder joints.
As you will see on the bottom is GND plane to provide enough large area to dispense heat and even maybe to attach it to the heatsink.

Regards,
Ales
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File Type: jpg TPS7A_PCB.JPG (97.1 KB, 2001 views)
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Old 21st April 2014, 12:03 PM   #2
stormsonic is offline stormsonic  Slovenia
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R2, R4 daj čimbližje izhodu, kjer je priklopljeno breme. Več na ZS, da ne smetim.
R2, R4 put closer to the output, where load is connected. More on PM.
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Old 21st April 2014, 12:29 PM   #3
Devilsdance7775 is offline Devilsdance7775  Australia
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Quote:
Originally Posted by stormsonic View Post
R2, R4 daj čimbližje izhodu, kjer je priklopljeno breme. Več na ZS, da ne smetim.
R2, R4 put closer to the output, where load is connected. More on PM.
Dont put R2,R4 closer to the output cause you dont know what additional parasite inductance will bring into error amplifier circuit. (or make an alternative connections, so you can choice letter on)

About QFN pads, get the size from data sheet. Make it a bit bigger for your own safety.
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Old 21st April 2014, 02:15 PM   #4
stormsonic is offline stormsonic  Slovenia
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Quote:
Originally Posted by Devilsdance7775
Dont put R2,R4 closer to the output cause you dont know what additional parasite inductance will bring into error amplifier circuit. (or make an alternative connections, so you can choice letter on)
Really?
Longer trace won't introduce any additional parasitic inductance into error amp. Longer trace will only introduce negligible voltage output error (inductive reactance * 350nA current through FB pin), since R2 is sense node, similar like ADJ pin on LM317 regulator.
Mixing Sense/Force track is bad, if you want low noise. Running force current through sense track will introduce voltage noise, for example, running 100mA through 1miliOhm will give you 100uV.
Look into datasheet, Figure 23. Or check excellent Walt Jung papers. Or Salas shunt regulator thread. Or Peufeu's explanation here.
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Old 21st April 2014, 03:45 PM   #5
MisterRogers is offline MisterRogers  United States
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Low noise symmetrical PSU TPS7A4701 and TPS7A3301
Looks good Ales - Definitely something I could use.
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Old 21st April 2014, 04:05 PM   #6
androa76 is offline androa76  Slovenia
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Wery good... Can you also made some 3pin mini regulator for hifi gear replacement.
Like this one...
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Old 22nd April 2014, 06:42 AM   #7
Devilsdance7775 is offline Devilsdance7775  Australia
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Quote:
Originally Posted by stormsonic View Post
Really?
Longer trace won't introduce any additional parasitic inductance into error amp. Longer trace will only introduce negligible voltage output error (inductive reactance * 350nA current through FB pin), since R2 is sense node, similar like ADJ pin on LM317 regulator.
Mixing Sense/Force track is bad, if you want low noise. Running force current through sense track will introduce voltage noise, for example, running 100mA through 1miliOhm will give you 100uV.
Look into datasheet, Figure 23. Or check excellent Walt Jung papers. Or Salas shunt regulator thread. Or Peufeu's explanation here.
trust no one but me do not move these resistors
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Old 22nd April 2014, 09:16 AM   #8
mravlca is offline mravlca  Slovenia
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Originally Posted by androa76 View Post
Wery good... Can you also made some 3pin mini regulator for hifi gear replacement.
Like this one...
I will design one, with programmable output and with sensing circuit, to use it for 3.3V and 5V, +/-12V will be using same scheme as in first post.

Quote:
Originally Posted by stormsonic View Post
R2, R4 daj čimbližje izhodu, kjer je priklopljeno breme. Več na ZS, da ne smetim.
R2, R4 put closer to the output, where load is connected. More on PM.
Looking at TPS7A4701 EVM those two resistors are as close a possible to the regulator. Also current through the FB is 35nA when having R2 value of 10kohm.

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Originally Posted by Devilsdance7775 View Post
trust no one but me do not move these resistors
As I see it I will have to trust measurements and nobody else

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Originally Posted by MisterRogers View Post
Looks good Ales - Definitely something I could use.
If there will be good results than I might make some ready build boards.

Stay tuned

Best Regards,
Ales
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Old 22nd April 2014, 09:33 AM   #9
stormsonic is offline stormsonic  Slovenia
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Old 22nd April 2014, 10:29 AM   #10
Devilsdance7775 is offline Devilsdance7775  Australia
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Originally Posted by stormsonic View Post
makes sense
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