- Mon Jun 22, 2015 2:46 pm
#21268
I run that same setup, and I leave the USB adapter unconnected to Vcc. It seemed to work with it connected, but this doesn't seem like a good idea. Also, with it disconnected the ESP is never powered off the USB, which is a good thing considering how much current it draws. You have to have the external power supply hooked up.
Moderator: igrr
- Mon Jun 22, 2015 8:00 pm
#21302
It doesnt seem like good practice but I thought maybe the 3.3v ftdi supply was designed to also be externally powered.
from FTDI data ..
+3.3V output from integrated LDO regulator. This pin should be decoupled to ground using a 100nF capacitor. The main use of this pin is to provide the internal +3.3V supply to the USB transceiver cell and the internal 1.5kΩ pull up resistor on USBDP. Up to 50mA can be drawn from this pin to power external logic if required. This pin can also be used to supply the VCCIO pin.
So no, its a low impedance output and would likely get very upset if voltage exceeds 3.3v and if excess current is drawn is going to spike the USB transceiver which will cause comms issues.
Leave it disconnected if you use external 3.3v.
from FTDI data ..
+3.3V output from integrated LDO regulator. This pin should be decoupled to ground using a 100nF capacitor. The main use of this pin is to provide the internal +3.3V supply to the USB transceiver cell and the internal 1.5kΩ pull up resistor on USBDP. Up to 50mA can be drawn from this pin to power external logic if required. This pin can also be used to supply the VCCIO pin.
So no, its a low impedance output and would likely get very upset if voltage exceeds 3.3v and if excess current is drawn is going to spike the USB transceiver which will cause comms issues.
Leave it disconnected if you use external 3.3v.
- Mon Jun 22, 2015 10:07 pm
#21308
If I wire up 2 1.5 volt batteries in series I get 3 volts
If I wire up 2 more and put them in parallel you will find that an acceptable 3 volt supply
So if I connect two DC power supplies in parallell what is the objection?
there may be some parasitic fluctuation but one will even out the other . Put a cap across if you wish but I can see nothing wrong with this.
If I wire up 2 more and put them in parallel you will find that an acceptable 3 volt supply
So if I connect two DC power supplies in parallell what is the objection?
there may be some parasitic fluctuation but one will even out the other . Put a cap across if you wish but I can see nothing wrong with this.
Last edited by tytower on Tue Jun 23, 2015 12:21 am, edited 1 time in total.
- Mon Jun 22, 2015 11:17 pm
#21316
firstly .. wire 2 1.5 volt batterys in you get 3v, not sure where 5v comes from ?
put 2 more in parallel, its still 3v.
also active regulators are not batterys.
connect the output of 2 regulators together (which is what is happening in the OP) you may get high frequency osicllations, or you may not .. if you apply 3.4v to a 3.3v regulator .. it may conduct excess current .. or it may not .. it might attempt to crowbar the excess to voltage to ground, or it may not.
apply 3.2v to a 3.3v regulator and the 3.3v reg will attempt to put out more current to drag the powe supply out of the stone ages and up to 3.3v where it thinks it should be, does this exceed the 50mA max of the ftdi .. depends on the power supply design, wire resistances and internal impedances of both supplys.
basically without knowing exactly what is going on design wise in the ftdi chip, its all guesswork. batterys are VERY forgiving in comparison, however .. apply 12v to a 6v battery and see what happens, its similar in this scenario.
you cannot charge a regulator.
basically applying 3.3v is very unlikely to damage it .. apply anything more and all bets are off.
tytower wrote:If I wire up 2 1.5 volt batteries in series I get 5 volts
If I wire up 2 more and put them in parallel you will find that an acceptable 5 volt supply
So if I connect two DC power supplies in parallell what is the objection?
there may be some parasitic fluctuation but one will even out the other . Put a cap across if you wish but I can see nothing wrong with this.
firstly .. wire 2 1.5 volt batterys in you get 3v, not sure where 5v comes from ?
put 2 more in parallel, its still 3v.
also active regulators are not batterys.
connect the output of 2 regulators together (which is what is happening in the OP) you may get high frequency osicllations, or you may not .. if you apply 3.4v to a 3.3v regulator .. it may conduct excess current .. or it may not .. it might attempt to crowbar the excess to voltage to ground, or it may not.
apply 3.2v to a 3.3v regulator and the 3.3v reg will attempt to put out more current to drag the powe supply out of the stone ages and up to 3.3v where it thinks it should be, does this exceed the 50mA max of the ftdi .. depends on the power supply design, wire resistances and internal impedances of both supplys.
basically without knowing exactly what is going on design wise in the ftdi chip, its all guesswork. batterys are VERY forgiving in comparison, however .. apply 12v to a 6v battery and see what happens, its similar in this scenario.
you cannot charge a regulator.
basically applying 3.3v is very unlikely to damage it .. apply anything more and all bets are off.
