Hi,
First, I know that CC1310 supports using a GPIO for a 32.768 kHz input square wave signal.
I intend to use si time SiT1552. This device has many configurations for its output signal, also with reduced voltage swing to minimize current consumption (load current).
Question 1:
However, the most ideal way would be to feed this signal into one of the actual pierce oscillator inputs. This way the voltage pk to pk swing can be reduced which then will minimize the load current for the TCXO ouput. SI Time has an application note https://www.sitime.com/api/gated/AN10037-SiT15xx-Optimized-Settings-for-32kHz-Inputs-MCUs.pdf which demonstrates this for some MCU devices. Could TI look into this?
Question 2A:
Another approach could be to configure an IO as digital 32 kHz input (the normal approach) and utilize the the different voltage supply domains offered by the CC1310.
The SiT1552 can operate from 1.5V to 3.63V. In our application the battery has a nominal output voltage of 3.6V.
Hence using a diode or more in series to lower the supply voltage (originating from 3.6V) for both the TCXO and VDDS2 would reduce the output voltage swing from the TCXO, which reduces the switching load current.
Would this work?
Question 2B:
Another idea that popped up would be to use the VDDR as power source for the TCXO - since this is on even in standby mode. I know that this pin should not be used to power any external circuitry.
However, this TCXO only requires 1 uA on the average, and with a peak current of 28 uA during startup.
So my question is, will this be OK due to the low current, even though the datasheet states that no external circuitry should be put on VDDR?
HC
