EG915U electrical characteristics regarding PWRKEY, MAIN_DTR, MAIN_RI

IoT Modules LTE Standard Module
1

Hello,
I have a few questions about the electrical characteristics of the PWRKEY pin and the UART pins of the EG915U-EU module. Unfortunately, the hardware design document (v1.1) leaves a few questions unanswered.

  1. The PWRKEY pin is an input (DI, as called in the hardware design document), but probably has a pull-up to VBAT. How big is this resistance to VBAT signal or what current do I have to sink to pull the pin to 0V?

  2. The hardware design document says: “When using AP_READY, MAIN_DTR, and MAIN_RI (pins 19, 30, and 39), please note that these pins will have a period of variable level state (not controllable by software) after the module is powered on: at high level (3.0 V) for 2 s and then at low level (0 V) for 1.2 s before they can be configured as 1.8 V input or output.” …
    What does that mean? The document also states that the UART pins belong to the 1.8V voltage domain. But is there still 3V on these pins for 2 seconds after power up (is that really 3V or simply VBAT)? What impedance do these pins have at 3V, is this a pull-up to VBAT, what currents should I expect when the 3V is discharged via the clamping diodes of my 1.8V microprocessor?

Thanks in advance,
Patrick

2

Hello,

For the first question, the document hardware design “EG915U_###_V1.1” p39/95 says " If the module needs to turn on automatically, PWRKEY can be driven low directly to ground with a recommended 1 kΩ resistor. However, ensure that the voltage of VBAT_BB and VBAT_RF pins are below0.5 V before power-up."

For your second question, I think that means, during startup the voltage level is not set internally yet, you have to wait before using it. A good thing to do is to use level shifter with Vdd_EXT as voltage ref for the modem side.

Hope it helps!