In SAR applications, Semtech SX9331 CAP sensor can detect whether a human body is approaching. When a human body is approaching or moving away, SX9331 sends an interrupt notification to the Host or DSP, and the Host or DSP decides whether to reduce the RF power to ensure that the human body receives The electromagnetic radiation received will not exceed the standard to ensure compliance with SAR regulations.

When the Host or DSP does not detect a CAP sensor, the Host or DSP must reduce the RF power to the RF power where a human body is approaching to ensure compliance with SAR regulations.

But how to detect whether there is an error in the CAP sensor?

Because the communication interface between SX9331 and Host or DSP is I2C, you can first use I2C to read the I2C slave address of SX9331. As long as there is an ACK reply from the I2C interface of SX9331, the SX9331 CAP sensor can be initially detected. But in order To be on the safe side, it is recommended to read the register address 0x42D8 of SX9331 and ensure that the received data is 0x3117. This will ensure that SX9331 is detected.

But if the SX9331 CAP sensor is detected, does it mean that the SX9331 can operate normally? Of course there is no way to guarantee this, but it can be combined with the FAILSTAT function of the SX9331 to further ensure that the sensing environment of the sensor pad is normal to avoid sensor pad failure. Or the hybrid antenna has abnormal contact or is short-circuited to ground.

This article is to introduce how to set up SX9331 Failure detection. Because SX9331 will first perform environmental correction compensation after power on. After completing the correction compensation, the compensation values ​​will be obtained as shown below, and the value is 1615.

In the Digital-Advanced part of SX9331, there is a Failure Detection page that can be set. Based on the compensation values ​​​​that can be operated normally on the PCBA board, the upper limit is 1920 and the lower limit is 1280. Set the upper and lower limits to threshold, when the power is on or after compensation, if there is no antenna or short circuit, the compensation values ​​will be abnormal. As long as it exceeds the upper or lower limit, SX9331 will send an interrupt to notify the Host or DSP. Only when there is a short circuit or no After troubleshooting the antenna connection, perform compensation or power on again to restore the value to the upper and lower limits of the threshold, then the Failure Detection state can be eliminated.

Fail condition register address: 0x800C bit 23.

Failure detection threshold hold register address: 0x8070 [15:8] and 0x8070[7:0]

When failure detection occurs, when the Host or DSP receives the interrupt, it can confirm register address 0x8004 [29:24]. As long as the read value is not 0, an error state has been detected.

During FCC certification, specific content will be required to explain how the CAP sensor is installed on the product and how the corresponding SAR test operates. Only when the CAP sensor is detected and confirmed to be working properly and away from the human body can the CAP sensor be used. RF power works at optimal power to ensure that the electromagnetic radiation received by the human body does not exceed the SAR standard. When used with the Semtech SX9331 CAP sensor, it can fully meet the requirements of FCC certification and ensure that the product can successfully pass certification and be launched on the market.

Semtech PerSe core technology advantages

The SX9324/SX9331 is a capacitive specific absorption rate (SAR) controller.

The SX9324/SX9331 can use two sensor inputs coupled to its smart

SAR's engine accurately differentiates between an inanimate object and a human body.

The resulting detection is used in portable electronic devices to reduce and control radio frequency (RF) transmit power

Significant performance advantages for electronics manufacturers in the presence of the human body

Devices with electromagnetic radiation sources are subject to strict emission regulatory standards and specific absorption rate (SAR) standards.

FAQs

Q: How to perform environmental compensation correction?

Answer: SX9331 compensation can be manually requested by the MCU through I2C at any time, or automatic compensation can be completed by restarting Phase.

Q: How to manually request compensation correction?

Answer: For SX9331 compensation, you need to first set 0X8020 to define the phase to be compensated when the host sends a compensation command. After the setting is completed, the MCU can manually request compensation for the phase specified by COMPEN through I2C at any time, or you can complete automatic compensation by restarting Phase.

Q: Will automatic correction be performed when turning on the machine?

Answer: It is generally recommended to place PHEN in the last step of initialization so that it can automatically correct the environment when starting.

Question: How many detection channels does SX9331 have?

Answer: SX9331 has a total of 5 sensor inputs (CSIO0, CSIO1, CSIO2, CSIO3 and CSIO4)

Question: Can two SX9331s share a set of I2C be recognized?

Answer: The default address of SX9331 is 0x28 (b0101000). If the CSIO2 of one of the SX9331 is grounded during reset (power-on or software), bit 2 will be set and the address will be changed to 0x2C (b0101100).