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#apertus IRC Channel Logs

2020/05/01

Timezone: UTC


03:00
metal_dent[m]
Good morning!
03:07
Bertl_oO
morning metal_dent[m]!
03:28
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06:45
Bertl_oO
off to bed now ... have a good one everyone!
06:45
Bertl_oO
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07:55
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08:01
BAndiT1983|away
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10:00
BAndiT1983
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BAndiT1983|away
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11:15
BAndiT1983
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11:40
se6ast1an
good day
11:47
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12:37
Bertl_zZ
changed nick to: Bertl
12:37
Bertl
morning folks!
12:39
se6ast1an
good day
12:42
BAndiT1983|away
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13:14
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14:04
vup
Bertl: on the micro r3 we will have two usb ports
14:04
vup
any recommendations on how to connect their vbus together?
14:04
vup
is there a better solution than just using two schottky diodes?
14:06
Bertl
vbus in or out and what is the purpose of the ports?
14:08
vup
vbus in
14:09
vup
they are used as the power source
14:09
vup
(and for data output)
14:09
Bertl
so the idea is to feed power from both sources?
14:09
vup
kind of
14:10
Bertl
any specific reason for that?
14:10
vup
switching between one of them would be enough
14:10
vup
well if we have two usb ports it would be nice, if either could be used for powering the camera
14:11
Bertl
how much power are we talking about?
14:12
vup
3A @ 5V
14:12
Bertl
you are negotiating that with the USB port? :)
14:12
vup
no :)
14:13
vup
but usb type c allows hosts to provide up to 3A without negotiation
14:13
Bertl
well, you could use P channel mosfets instead of shottky diodes
14:14
vup
does that actually help? the ones i found has a Rds(on) of ~50mΩ, which is still a 150mV voltage drop at 3A
14:16
Bertl
a quick check @ mouser gives starting at 1.5mOhm
14:17
Bertl
how much PCB space do you have available?
14:18
vup
unclear
14:18
vup
but shouldn't be too tight currently
14:20
Bertl
https://www.mouser.at/datasheet/2/115/DMP1005UFDF-1142690.pdf
14:52
vup
would you use a ideal diode controller with that or build one discretely?
15:09
Bertl
neither, just connect the gate to GND use the source on the input and the drain as output
15:10
Bertl
if you want to make the inputs selectable, add a dual NPN stage as low voltage 'enables'
15:31
vup
wait I thought mosfet's provide no inherent reverse current protection?
15:31
vup
if I just connect the gate to GND and connect both usb ports, won't one feed the other?
15:37
Bertl
drain to source happens via the body diode, which has a forward voltage of 0.8V
15:38
Bertl
assuming that the 5V supplies are within the spec this should prevent any reverse current
15:38
Bertl
but if you want to play it safe, you can add a controller or discrete circuitry as well
15:42
vup
ah right as long as both supplies are 5V is should work
15:42
vup
I think thats a safe assumption
15:43
Bertl
5V +/- 0.7 or so
15:43
Bertl
well, let's say |V1-V2| < 0.7 :)
15:43
vup
yeah
15:50
Bertl
but you can use a comparator (or dual comparator) to shut off any of the two mosfets
15:51
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16:00
Anoop
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16:21
megora
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16:45
Bertl
off for now ... bbl
16:45
Bertl
changed nick to: Bertl_oO
17:14
vup
Bertl_oO: Hmm I am still not convinced what you propose will actually work. To reiterate, I have two usb ports and want to prevent current from going into the usb port.
17:14
vup
You propose connecting a p channel mosfet with gate tied to GND, source connected to vbus and drain connected to the shared 5V net to each of the two vbus's.
17:14
vup
Now suppose both ports are connected and port 1 has a voltage of 4.9V and port 2 a voltage of 5V.
17:14
vup
Both mosfets will be on (as Vgs will be > Vth), I would think current would flow from port 2 to the shared 5V net. And now because the mosfet of port 1 will also be on, won't the current flow through that mosfet aswell?
17:44
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18:06
BAndiT1983
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19:25
BAndiT1983|away
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22:10
panintended
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22:11
BAndiT1983
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22:42
se6ast1an
off to bed
22:42
se6ast1an
good night
22:43
panintended
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23:07
alexML
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23:07
comradekingu
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23:50
Bertl_oO
vup: yeah, you're right ... doesn't work without additional active circuitry
23:51
Bertl_oO
some kind of comparator which turns off the mosfet when the output voltage is above the input level
23:51
vup
ok makes sense
23:53
Bertl_oO
it works quite fine as reverse polarity protection because the gate is at a higher level in this case
23:53
Bertl_oO
but it doesn't help with competing inputs
23:53
vup
yeah
23:53
vup
i got confused by that at first aswell
00:28
vup
well the FPF1048 seems like a neat solution
00:30
Bertl_oO
indeed