Using the PWR_KEY pin for wake up in an emegency

Hi,

I am using the BC66 module in a tiny PCB with a very small battery (3V).

The application is very easy, a button connected to the PSM_EINT pin, in order to wake up and send a message to a server.

The problem is that at the end of the life of the battery and due to the fact the BC66 module has peak currents about 350mA, occasionally the voltage can drop off 2.1 Volts, and then, the module goes to an unknown state, and it is not going to wake up anymore. Therefore, the only way to switch on the module BC66 again, is generating a falling down signal in the pin PWR_KEY.

Therefore, I tied the two pins PWR_KET and PSM_EINT together. Everything is working perfectly. In this way, if the module goes to an unknown state due to the fact Vbatt < 2.1 Volts, when you press the button the next time, the module will work again.

So far so good, but recently I’ve read this note in the document: Quectel_BC66_Hardware_Design_V1.2.pdf

PWR_KEY cannot be pulled down all the time, otherwise the module will not able to enter into PSM.

I am only pressing the PWR_KEY + PSM_INT in the first beginning.

So I have a lot of doubts If I can do what I am doing. I didn’t notice that the module didn’t go to PSM mode, but I am a bit concerned about this issue.

I need to go production with around 5k units. So I need to have this issue very clear and solved to be calm.

Best regards.

Hi Oscargomezf
It is not recommended that you use it this way.
pwr_key has power on and power off function.
If you do not control Timing when you press a button, it will cause the module to shut down.

The only way to switch on the module BC66 again, is generating a falling down signal in the pin PWR_KEY.
I suspect that the module is already in the shutdown state, not the PSM state, so PSM_INT cannot wake up.

Hi Abner,

Thank you very much for your help.

So, you told me: “pwr_key has power on and power off function.”. I know the function: “power on the BC66”:

image

But I didn’t know that with the PWR_KEY you can power off the module BC66. Do you know how much time do I have to low the signal PWR_KEY to switch off the module?

If this behaviour can be a problem for my application and in order to avoid powering off the module BC66, it could be a solution to add some electronics in order to detect a falling signal on PWR_KEY and fixed this time to a maximum of 800msec, for example, in order to avoid powering off the module BC66.

Best regards.

Hi Oscargomezf
The shutdown function of PWR_KEY has been closed, you can only use AT + QPOWD = 1 to shut down.
If you turn off the PWR_KEY shutdown function, the previous function is theoretically feasible.

Hi Abner,

1º. So then, according to: “It is not recommended that you use it this way.
pwr_key has power on and power off function.
If you do not control Timing when you press a button, it will cause the module to shut down.”

Therefore this statement is wrong and I can use PWR_KEY like I said, that is to say:

The problem is that at the end of the life of the battery and due to the fact the BC66 module has peak currents about 350mA, occasionally the voltage can drop off 2.1 Volts, and then, the module goes to an unknown state, and it is not going to wake up anymore. Therefore, the only way to switch on the module BC66 again, is generating a falling down signal in the pin PWR_KEY.

Therefore, I tied the two pins PWR_KET and PSM_EINT together. Everything is working perfectly. In this way, if the module goes to an unknown state due to the fact Vbatt < 2.1 Volts, when you press the button the next time, the module will work again.

2º. But, what about the note in the datasheet: Quectel_BC66_Hardware_Design_V1.2.pdf

PWRKEY cannot be pulled down all the time, otherwise the module will not be able to enter into PSM

Best regards.

Hi Oscargomezf
pwr_key has power on and power off function.
Previously, shutdown was supported, and now the latest version and later versions have turned off this feature.

PWRKEY cannot be pulled down all the time, otherwise the module will not be able to enter into PSM.
When PSM_EINT does not enter PSM, it is low level. When PWR_KET and PSM_EINT are connected together, PWR_KET is always at low level, which will prevent the module from entering deep sleep mode.
So you are still not feasible this way.

When PSM_EINT does not enter PSM, it is low level.

Isn’t PSM_EINT working on falling edge? Both PSM_EINT and PWR_KEY work with same level (active low), they just differ in how long you need to hold it low.

1 Like

Hi everyone,

Yes @rastik, I can ensure this statement: “Both PSM_EINT and PWR_KEY work with same level (active low)”, because I tested it. But I am concerned about that occasionally due to the note in the datasheet: Quectel_BC66_Hardware_Design_V1.2.pdf: “PWRKEY cannot be pulled down all the time, otherwise the module will not be able to enter into PSM”, the module couldn’t enter in PSM mode.

Therefore, in order to avoid activating PWRKEY after the BC66 module starts when I activate the PSM_EINT signal, and so as to be at 100% that the module is going to enter in PSM mode, this is my circuit proposal:

With this driver we can ensure only a pulse in the init, so if the module BC66 is off, due to the Vbat was less than 2.1 Volts and because of the fact the signal VDD_EXT is low, we are going to be able to switch on the module BC66, but as soon as the device wakes up the VDD_EXT is going to be 1.8Volts and the buffer will be disabled.

So I only have to check this, burt before doing that, Do you think @Abner-Q this is good enough? Would you mind asking Quectel engineers?

Best regards.

@oscargomezf I was more replying to the info from @Abner-Q. Personally, I think that your should work (probably even the simple one - just connecting both inputs together). But you need to make sure the user is pressing the button for at least 500 ms, or PWRKEY will not work.

Yes @rastik,

I can ensure that the user is going to press the button for more than 500msec, but the user is going to press the button several times for 20-30 seconds, so I am aware for the note in the datasheet: Quectel_BC66_Hardware_Design_V1.2.pdf

PWRKEY cannot be pulled down all the time, otherwise the module will not be able to enter into PSM

This is the reason I want to design some kind of circuit to avoid being the PWRKEY pin activated for more than once.

Best regards.