BQ25606: BQ25606: USB power detection in embedded device (D+/D- lines) without sacrifice DCP detection.

Pierre Girard

Part Number: BQ25606
Other Parts Discussed in Thread: TS3USB221A

Hi,

As mr Hoferichter in this resolved post i have to use the same USB port for charging and communcation (Through Ft232) on a schematic for an embedded device.

After having carefully read the solution proposed to mr Hoferichter I ask myself the following question:

By putting two 150 Ohm resistor in line between the charger and the D+/D- bus would involve to sacrifice the DCP mode detection ?

If yes, what are the solution to save all charger type detection without disturbing communication?

over 7 years ago

0 Joel Hernandez II over 7 years ago

TI__Mastermind 25800 points

Hey Pierre,

Putting two 150 Ohm resistors in line with D+/D- should not impair the DCP port detection.

While the USB BC1.2 spec specifies a 'Rdcp_dat' max of 200 Ohm. However, upon further inspection, the detection define in the sepc itself allows for further resistance on the DCP port. Based on the bq25606's worst case: minimum Vdp_src voltage of 0.5V and maximum Idm_sink of 150uA, we find that the largest resistance between the D+ and D- pins of the charger (including the DCP adapter itself) is ~667 Ohms. If we subtract out 200 Ohm, you are left with ~230 Ohm of margin on each individual line.

However, for an alternative solution, I can suggest using a USB switch such as the TS3USB221A. This would require a driving signal to switch the Mux between USB connections.

Regards,
Joel H

0 Pierre Girard over 7 years ago in reply to Joel Hernandez II

Prodigy 60 points

Hi Joel,
Thanks for the explanation,

I'll put the 150Ohm resistor on my prototype and if it's unstable, the TS3USB221A will be a good option.

Thanks a lot for your help,

Goodbye,

Pierre

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BQ25606: BQ25606: USB power detection in embedded device (D+/D- lines) without sacrifice DCP detection.