nRF9160 COEX2 pin 100k pull-down

[Lukáš]

Hi,

is the 100k pull-down on the COEX2 pin required as stated in the product specification? I don't see it being followed anywhere (reference circuitry, nRF9160 DK schematic, Thingy:91 schematic, etc.)

Best regards,

Lukas

[Sigurd]

Hi Lukas,

Jared is Out of Office, so I'm answering on his behalf.

We got confirmation today from the HW engineers that the pulldown is needed. COEX2 pin requires an external pull-down resistor in 100 kΩ size range to be used.

BR,

Sigurd

[Lukáš]

Hi Sigurd,

thanks for the reply. Could you please explain, why the 100k pulldown is not used in nRF9160 DK or Thingy:91 even when the pin is routed between nRF91 and nRF52?

Lukas

[Sigurd]

Hi,

Most likely because it was originally not needed, but it was later needed when the COEX2 pin got the extra functionality to also serve as "active low grant to external (BLE) device". When the LTE modem domain is powered down / deep sleep, the COEX2 pin will go to input mode with no pull(floating), for the COEX2 pin to function as described in the PS, the pulldown is then needed. It might be enough that the BLE chip uses its internal pull-down for this (13k ohm on nRF52x). In that case, an external resistor might not be needed…. I will double check this with the HW engineers.

Note that as of today, both the BLE and LTE side has the option to output an signal, but none of them has the option to yield for an input signal.

[Sigurd]

Sigurd said:

It might be enough that the BLE chip uses its internal pull-down for this (13k ohm on nRF52x). In that case, an external resistor might not be needed…. I will double check this with the HW engineers.

 The answer to this is:

Functionality wise, no extra pulldown expected needed then, but current leakage wise, the larger extra pulldown causes less current leak in modem active mode, when modem drives the pin high (= indicating no-GRANT). Whether this is a critical difference, may be customer use case dependent.