usbpicprog-technical

Re: [Usbpicprog-technical] USB electrical characteristics

[Frans S. <fra...@gm...>]

Hi Francesco,

Sorry for not responding, I just opened these mailing lists and discovered
that I forgot to subscribe myself!
Don't worry too much about the current consumption of usbpicprog, it will
draw 50mA max. It can also work from 4.2V.

What you do have to worry about is connecting a target board which is
powered by usbpicprog. If that one draws more than about 300mA, give it his
own powersupply of 5V.
Because of the diode in the VDD connection, it is allowed to use a 5V power
supply (but don't use a lower voltage than 4.5V when usbpicprog is trying to
power up the target board)

Cheers,

Frans

> Hi all,
> I looked at the USB specs taken from usb.org (file usb_20.pdf,
> paragraph 7.2.1) and I've found that any device attached to a USB port
> should be able to work with a Vbus down to 4.4V and is allowed to draw a
> maximum of 100mA upon power-up and a maximum of 500mA after
configuration...
>
> Are those data correct?
>
> How much current does usbpicprog draws from the USB port?
>
> Thanks,
> Francesco

Re: [Usbpicprog-technical] USB electrical characteristics

[Francesco M. <f18...@ya...>]

Hi,

Frans Schreuder ha scritto:
> Sorry for not responding, I just opened these mailing lists and 
> discovered that I forgot to subscribe myself!
no problem ;)

> Don't worry too much about the current consumption of usbpicprog, it 
> will draw 50mA max. It can also work from 4.2V.
very good.

> What you do have to worry about is connecting a target board which is 
> powered by usbpicprog. If that one draws more than about 300mA, give it 
> his own powersupply of 5V.
ok; but what about Vpp?
The charge pump can deliver only a very small current; I've simulated it (using 
a square wave on Vpump1 and Vpump2 at about 20kHz) and absorbing 1.5mA makes Vpp 
drop to 9V....

OTOH I couldn't find any specs about the minimal current which this pin should 
be able to provide... I've found references to a LVP (low-voltage programming) 
mode, where Vpp is used only as a voltage reference (if I got it right); while 
in non-LVP mode, Vpp is used as source for the EEPROM programming.
I may be wrong however...


> Because of the diode in the VDD connection, it is allowed to use a 5V 
> power supply (but don't use a lower voltage than 4.5V when usbpicprog is 
> trying to power up the target board)
sure; I guess that powering the external circuit with < 4.5V would turn on that 
diode, and provoke a large current flow through the PMOS, leading to its 
possible destruction...

Thanks,
Francesco


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Re: [Usbpicprog-technical] USB electrical characteristics

[Francesco M. <f18...@ya...>]

Frans Schreuder ha scritto:
>     ok; but what about Vpp?
>     The charge pump can deliver only a very small current; I've
>     simulated it (using a square wave on Vpump1 and Vpump2 at about
>     20kHz) and absorbing 1.5mA makes Vpp drop to 9V....
> 
>     OTOH I couldn't find any specs about the minimal current which this
>     pin should be able to provide... I've found references to a LVP
>     (low-voltage programming) mode, where Vpp is used only as a voltage
>     reference (if I got it right); while in non-LVP mode, Vpp is used as
>     source for the EEPROM programming.
>     I may be wrong however...
> 
> 
> According to Microchip's programming specification:
> 
> /To activate the Programming mode, high voltage needs to be applied to 
> the MCLR input. Since MCLR is used for a
> level source, this means that MCLR does not draw any significant current./
> 
> So also don't worry about that one!
Ok, thanks for the reassurance!


Francesco


PS: probably the reply-to header field of the mailing list should be set to the 
"list" instead of to the "poster".
You can find this setting in the [general options] GNU mailman admin page of the 
mailing list, at the row containing "Where are replies to list messages 
directed?"...

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