WL1805MOD: What are the characteristics of GPIO11 (Audio SYNC) pin?

Petr Mlynar

Part Number: WL1805MOD

Hello,

we want to use WLAN synchronization due the help of GPIO11. However its unclear what are the proper characteristics of this pin for the connection.

I didn't find anywhere in the specification what is the pulldown resistor. We connected resistor divider from 3.3V level to 1.8V kevel as it is described in https://www.ti.com/lit/an/swra448a/swra448a.pdf?ts=1614021712481 for WLAN enable line. It works fine for WLAN_ENABLE as there is clearly specified 200kOhm pulldown resistor. However for GPIO11 we see after resistor division 1.2V on the output. This is apparently not sufficient to reach high level. It seems that there is a pulldown about 10kOhm on this pin. We also measured second board and we got slighlty different values. So it ranges somehwere around 9 - 11kOhm.

It would be nice to know more details about this pin.

Thanks.

over 2 years ago

0 Seong Kim over 2 years ago

TI__Mastermind 40735 points

Petr,

Please see this related thread: https://e2e.ti.com/support/wireless-connectivity/wi-fi-group/wifi/f/wi-fi-forum/753464/wl1837mod-internal-pull-up-and-pull-down-values/2787558#2787558

BR,

Seong

0 Petr Mlynar over 2 years ago in reply to Seong Kim

Intellectual 615 points

Hi Seong,

thanks for the link but it doesn't fit to GPIO11 as we measure completely different values around 10kOhm.

0 Seong Kim over 2 years ago in reply to Petr Mlynar

TI__Mastermind 40735 points

Petr,

How are you measuring the internal pull down resistor?

BR,

Seong

0 Petr Mlynar over 2 years ago in reply to Seong Kim

Intellectual 615 points

We use resistor divider for GPIO11 pin as described here (https://www.ti.com/lit/an/swra448a/swra448a.pdf?ts=1614021712481) for WLAN_ENABLE pin and the voltage on the output is 1.2V which corresponds to a internal pulldown resistor with value of 10kOhm.

0 Seong Kim over 2 years ago in reply to Petr Mlynar

TI__Mastermind 40735 points

Peter,

That does not constitute as a voltage divider because it is the other way around; a resistor tied to GND and then a resistor in series.

A voltage divider circuit is shown below. It is a series resistor first followed by a resistor tied to GND.

What is the resistor value that you are connecting to GPIO11?

BR,

Seong

0 Petr Mlynar over 2 years ago in reply to Seong Kim

Intellectual 615 points

Hi Seong,

please check attached schematics, I hope it will be clear now. We really need to know internal pulldown resistor value for GPIO11 to properly set R1 and R2 on the picture. Any other characterstics like allowed voltage range input is appreciated. (With values R1 = 2k7 and R2 = 4k7 it seems to work however measured voltage is then 1.93, which is slightly above 1.8V)