Hi Experts,
we are facing to a strange behaviour with our custom board that implements TQP3M9035 LNA.
In this board we need to drive the shutdown to bypass the LNA.
After we made several measure the LNA seems stop to work.
Normally we drive the shut down pin with these voltage levels measured directly on the pin:
- 50mV when it’s ON
- 750mV when it’s OFF
For some reasons, after some tests we are not able to power on the device with the shutdown pin, except if we heat the pcb.
Considering that:
- The shutdown pin drains current because the voltage on that pin in slightly difference respest to the “pure” voltage divider.
- The RFOUT pin has the voltage supply.
- We use the same connection as in the eval board.
How can I debug this issue?
Thanks.
What resistor network are you using on shutdown pin 6, and what is the incoming voltage level (3.3V or 5V).
When you heat the PCB to get the LNA to work, what is the approximate temperature?
If the fault is intermittent then this is most likely caused by an assembly issue, like poor solder joint. Have you investigated this?
I would investigate by first checking the supply current as you toggle the shut down voltage. Do you get the correct current when the LNA should be on? Worth checking if the on/off threshold has shifted with temperature. The part should turn on when the voltage on shut down pin 6 is below 100mV.
Thanks for your reply,
the resistor network that we have is of 5k6 from 5V to shutdown, and 1k between shutdown to gnd.
We haven’t measured the temperature and we have no information regarding assembly issues.
When the LNA is correctly on the current is ok.
When it should be on, it has the voltage on the pin at 50mV, we have margin on it. If the pin is floating the LNA should be on or off?
Thanks.
There are no internal pull up/down resistors on the shutdown pin that would force the LNA on or off.
When shutdown pin is left open or floating the voltage should pull down via some internal FETs in the bias circuit, turning the LNA on.