Yet another ultra low noise high PSRR LDO - LT3042

See below the relative noise density measurement between TPS7A4700, configured to 4,2V dc out, and a 'reference 60ohm' input impedance.
measurement tool: Gerhard's pre, (cca 220pV/sqrtHz) >>RTX6001 >> HpWorks

the 60ohm ref line is, equivalent to 1nV/SqrtHz noise spectral density
As a consequence, the TPSA74700 output noise spectral density comes 20dB higher, 10nV/SqrtHz.
 

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here there are all compared together: highest trace is TPS7A4700 (10nV/sqrtHz)
below LT3042, 4V dc out, 100mA load current, 10uF reference bypass cap (2nV/sqrtHz)
lowest trace is the 60ohm, 1nV/sqrtHz baseline reference
 

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Amazing thank you for sharing. This is what life should be, togheter we help each other and share our findings, to get the best products and to not be prey to marketing. Thank you. Edit : and to support the manufacturer of good products and fair prices ;)


Is it a good idea to use the pgfb (fast start resistor divider) to sink the 60mA ? Or should i use higher other values, and use a dedicated sink/load resistor ?
 
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And there is more to it than just the used ICs ;-)

You are correct. It is also important to choose the right tool for the job. To illustrate here are 3 measurements of the self noise (i.e. input shorted) of my 60dB LNA. The LNA is my take on Samuel Groner's LNA using 4 unmatched 2sk369 fets scavenged from an old scrapped Pioneer A443 amp.

1. LNA powered with SilentSwitcher + battery pack
2. LNA powered with my LT30xx switcher + battery pack
3. LNA powered with my LT30xx switcher + USB from the same workstation :eek:. Just look at those nasty spikes :D

To be fair LNA is not the optimum usage of SilentSwitcher. It is excellent e.g. with Jan's Autoranger.
 

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Hello I have a 15v output on my lt3045. So I used 150k resisitor as Rset. and 22uF Cset.
Since I buy my resistors by 10 (to get them cheaper) I have spares of 150k res.

Now I need set up fast startup for the 22uF Cset at 15V output. but i want to use 150k res in the divider. what value could i use for the other resistor ?

I read the datasheet, it said howto set up fast startup, I have the formula, but what is the good ratio in %, to charge up Cset ?

I need help. Thank you.

EDIT . my Cset in 16V rated, is it enough?
 
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the voltage divider of external resistors, RPG2 and RPG1 program the power good threshold and also activates the fast start-up circuit. Output voltages below 300 mV disable the programmable power good and fast start-up capabilities.
Can some one explain me how the fast startup work ?
Does it mean that when the PGFB pin hits 0.3V it will disable disable the 'fast charging' ?

I set the 3042 at 15v. so i have spare of cset 150k resistor i want to use to set Fast startup.

If I use 150k + 50k divider it means I am dumping a 75% of the output voltage (since the voltage divider is connected to Vout pin), so it will hit 0.3v at the PGFB pin (and stop fast charging) when the Vout pin is at 1.2V. Or does it mean I have set up fast charging at 75% ?

0.3v is 2% of 15v. if i want to set the PGFB pin to be at 0.3V when I hit 15Vout, I need 150k+3K voltage divider ?

Can you help me because I read the datasheet many times this full week and I can't understand.