<div dir="ltr">John,<div><br></div><div>Thank you for your breakdown on voltage regulators. Would you mind sharing some of your favorite part numbers in the "Modern BiCMOS LDOs"? </div><div><br>Thanks!</div><div>Shane</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Nov 16, 2020 at 5:52 PM John Wettroth via TriEmbed <<a href="mailto:triembed@triembed.org">triembed@triembed.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
<div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>I'll put my 2 cents in here for a few subtleties.
I defined probably 1000 different linear and switching regulators
at Maxim in my 25 years.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>Vout plus dropout is pretty good overall. But
don't forget that dropout is defined where the output voltage drops 100
mV. Its coming out of regulation and all the goodness that linears give
you stops happening. You also want to do this at max load, max output
tolerance and worst temp. The drop out for bipolars decreases for
higher temps which helps but at very cold temps, it can grow- a lot a very
cold. This is not allways well specified.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>There are several classes of dropout that are driven by
the design of the ouput stage</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>Vdropout</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>2v standard bipolar
linears like the 7805 use an NPN darlington output- nice low impedance and easy
to use.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>1v LM1117 type bipolar
linears use a Sziklai modified darlington with an NPN follower driven by a PNP-
pretty good comprimise</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>.5v LM2940 PNP pass element
parts have low dropout but some squirelly stability issues at times and can have
high quiescent at dropout</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>.1v PMOS or charge pumped NPN
pass element types that looks like a small resistance in dropout.
Quiescent can be very low.</span></font></div>
<div dir="ltr" align="left"><span></span><font face="Arial"><font size="2"><font color="#0000ff">.</font></font></font></div>
<div dir="ltr" align="left"><font face="Arial"><font size="2"><font color="#0000ff"><span>Depending on the type of regulator, there are subtlties
that happen around dropout.</span></font></font></font></div>
<div dir="ltr" align="left"><font face="Arial"><font size="2"><font color="#0000ff"><span></span></font></font></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>Old bipolar regulators like the 7805 have a drop out of
about 2v conservatively. The output is an emitter follower darlington
stage which is 2 vbe's (.7v each) and 2 Vce sat (about .2v each). This is
about 1.8v. Since the output is a follower, it has a gain
of 1 and are generally very well behaved with very little thought
given to bypassing and stability. High frequency rejection is poor and
accuracy is somewhat poor.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>First generation bipolar LDO's like the
LM2940 etc, used a PNP output stage with a grounded NPN pulling its base
down. These parts have two Vce sats in the dropout path (about .5v).
These transistors have gain on top of the error amp gain and get
unstable without following the the bypassing instructions closely. The
output cap becomes the dominant pole and the ESR of the output cap has to in a
specific range- neither two small or two large. The other annoying feature
of this class is as you approach dropout- the beta provided by the PNP
pass element goes south and they can draw lots of current at or near dropout
trying to keep the PNP in saturation. In low power circuits, this can
cause a sort of latching action and flatten a battery in no
time.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>The LM1117 type second gen bipolar LDO's have a NPN
follower ouput. These have the benefit of a follower but only moderate
dropout performance. They were basically invented to make 3.3v from 5v
which a 7805 couldn't do. Good for point of load but kind of mediocre
otherwise.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>Modern BiCMOS LDO's generally have a PMOS pass element
and some MOS and Bipolar circuits.. These can have very low quiescent,
very low noise and the lowest dropout possible. They are also pretty
stable with most loads but take a signicant cap on the output usually.
Something like a 10 uF ceramic. Microchip make some good low cost
parts in this class. Probably my favorites.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>There are all CMOS LDO's that share most of features of
the last category but don't get the low noise and high accurancy
generally.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>One other issue is your 8v battery. The charging
voltage on a Lead Acid could be over 10V which is a common abs max for many
linears.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span>My 2 cents.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" size="2" face="Arial"><span></span></font> </div>
<div> </div>
<p><font size="2">Regards,<br>John M. Wettroth<br>(984) 329-5420 (home)<br>(919)
349-9875 (cell) </font></p>
<div> </div><br>
<div lang="en-us" dir="ltr" align="left">
<hr>
<font size="2" face="Tahoma"><b>From:</b> TriEmbed
[mailto:<a href="mailto:triembed-bounces@triembed.org" target="_blank">triembed-bounces@triembed.org</a>] <b>On Behalf Of </b>Pete Soper via
TriEmbed<br><b>Sent:</b> Monday, November 16, 2020 10:46 AM<br><b>To:</b>
<a href="mailto:triembed@triembed.org" target="_blank">triembed@triembed.org</a><br><b>Subject:</b> Re: [TriEmbed] Powering ESP32 from an
8v golf cart battery<br></font><br></div>
<div></div>
<p><br></p>
<div>On 11/15/20 10:34 PM, The MacDougals via TriEmbed
wrote:<br></div>
<blockquote type="cite">
</blockquote></div>
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