Hello TI,
I seem to be having the same issue as was reported in the thread below:
I have LM1971 mounted on a custom PCB. We use 5V Vdd and 2.5V Vref. I am able to write to the device via SPI (logic analyzer attachments included.) I can successfully set the attenuation in any step between 0db to -20 db. However, if I attempt to se a higher attenuation (including 0x3F mute), the attenuation remains at -20 db. Also, we have run an experiment separate from our custom PCB where we apply 5V at Vdd and measure the resistance from In to Out. We are measuring about 35 kOhm under this condition, which indicates that the device is not coming out of POR in mute mode with In and Out disconnected, as suggested by the datasheet.
The E2E thread above suggests that the issue may be hardware related. We have tried devices with two separate date codes (four devices in total) and are seeing the same issue on all devices.
Here are the scope captures of SPI bus. These show sending an attenuation of 0x02 first and then an attenuation of 0x3F (mute.) The result is that the 0x02 will set the correct attenuation, but the mute will set about -20 dB. I can alternate the commands as many times as I want and they will have their respective effect, but the mute never goes to -100 dB.:
Here are the settings for the logic analyzer. They are the same as the SPI settings. I am using MSP432P401Y and the TI SPI driver.
Please let me know of any recommended next step to either isolate the root cause or fix the issue.
Thanks!
Steve
