FAQ
◦
I/O pins are configured in improper pull-up or pull-down state.
Above incorrect configurations can cause system leakage, so you need to properly configure the state of I/Os
before GR551x enters sleep mode.
•
Solution
Configure the state of I/O pins before GR551x enters sleep mode.
◦
If an I/O pin is in pull-up/pull-down state or used as a driver output, it needs no pull-up/pull-down
configuration.
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If an I/O pin is not used or works in input mode without pull-up or pull-down, it needs to be configured to
internal pull-down.
For sleep mode configurations, see
GR551x Sleep Mode and Power Consumption Measurement Application Note
.
5.3 Can the RF PI Circuits Be Simplified or Removed?
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Description
In designing a PCB, can I modify the recommended RF PI circuit layout due to limited space?
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Issue Analysis
GR551x recommends two PI circuits for RF: a PI circuit close to GR551x and a PI circuit close to the antenna.
Whether these two PI circuits can be simplified or removed needs to be treated differently.
•
Solution
The PI circuit close to GR551x is used to match GR551x internal PA and cannot be removed. It cannot be
simplified also as its inductance and capacitance values must be kept consistent with the recommended circuit.
The impedance of the RF channel from the GR551x PI is 50 Ω and compatible with any 2.4 GHz antenna (2400
MHz to 2484 MHz) that supports Bluetooth products.
The PI circuit close to the antenna end is used to match the antenna, and its circuit can be changed according to
the antenna you use. For the matching of the antenna, you can complete simple matching adjustment by the S11
parameter or the Smith chart from the vector network analyzer. However, for matching of other indicators (such
as antenna gain and directionality), you are recommended to seek help from professional antenna factories.
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