The LTE modem uses a dedicated three-pin interface for RF interference avoidance towards a companion radio device such as an external positioning device or Bluetooth® Low Energy device.
The interface has the following outputs:
- COEX0 – Output from the LTE modem to the external device. When internal GPS is used, COEX0 can be used as active high control for the external LNA component.
- COEX1 – Output from the LTE modem to the external device. When internal GPS is used, COEX1 delivers the GPS 1PPS (one pulse per second) time mark pulse. The 1PPS feature must not be used when LTE is enabled.
- COEX2 – Output from the LTE modem to the external device. When active high, this indicates that the LTE modem transceiver is turned on. COEX2 can also be treated as an active low grant from the LTE modem to the external device, indicating permission to transmit and receive.
Note: Using the COEX2 pin requires an external pull-down resistor in the 100 kΩ size range.
The COEX interface timing in relation to the LTE modem state is shown in the following figure.
Figure 1. COEX interface timing
