We have had three builds of a device using the LMX9838 module. On 60% of the last build only, the BT output power is down 10db. The design has not changed and they had no such problems with build one or two.
They did use another CM last time but x-rays and microscopic inspections show no obvious workmanship issues.
We would like to get a better understand the device markings (we do have a spec sheet but not all markings are explained) and would like understand the purposes of all ground pins – especially the ones that are not tied together. These two items may give us a clue.
The device markings are explained in detail at the link below.
Device Marking Conventions: http://www.national.com/en/quality/marking_conventions.html
Digital Field Applications
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Please let me know about the ground pins when you get a chance.
I am not sure I understand the question regarding the ground pins.
What exactly does the customer want to know?
There are several ground pins on the device. They spec sheet says they must all be connected to ground but gives no additional detail on what they do. Most are connected together. At least one pin is isolated and had less than normal solder on it on the two devices that we disassembled.
We would like to understand the function of all ground pins that are not connected together.
The ground pins are input pins that serve as the logic level low voltage reference for the device.
All ground pins (3,4,17,18,24,29,30,31,32) must be connected to the ground plane.
Proper layout of the ground plane is discussed at the following link.
LMX9838 layout: Grounding question: http://e2e.ti.com/support/low_power_rf/f/155/p/204371/725982.aspx#725982
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