CC1120 TCXO power control on DCPL_XOSC pin

Hi,

This 1.8V may not have enough drive capabilty to drive TCXO. So, it is better to use an External supply to the TCXO through a switch (transistor) and control the TCXO PS Switch (transistor) from one of the CC1120 GPIOs. Please see section 3.4 of CC112X user guide for GPIO mapping (table 10).

Thanks,

PM

Hi

I was looking for the same feature, since datasheet/user manual do not describe this, and I can see two different informations :

One says No : see post bove

One says yes : topic  Handling questions reg. design with CC11

The design reference seems to say yes.

What shall we do? Shall TCXO be powered by CC1200?

Unfortunately it's difficult to give a straight forward answer to this. We design the chip to have the performance in the datasheet for the temperature and voltage range stated. In addition the chip is designed to have the performance with variation in the production over time. The process variation will have a normal distribution and most wafers will then have parameters towards the middle. Close to 3-6 sigma and for combinations of high/ low temp and high/ low voltage is what analog designers refer to as corners. For a couple of these corners the LDO can only supply 1 mA and still be within spec. If the current is higher than 1 mA in this case the PSRR of the LDO will decrease. If the voltage is slightly higher than 2 V the LDO will not have any issues supplying 2 mA over all corners.  

Thanks for this answer.

If I go further, I would need to switch off the TCXO.

Can it be done if I connect the TCXO to DCPL_XOSC?

Shall I set XOSC2 bit 0 =0 ( XOSC_CORE_PD_OVERRIDE) to switch off DCPL_XOSC supply?

XOSC2.XOSC_CORE_PD_OVERRIDE is default 0 so you don't have to write this register if you want the regulator to turn off.

The DCPL_XOSC supply will be turned off when the XOSC is off, eq when a SWOR, SPWD or SXOFF strobe is sent.

Do the LDO require close decoupling capacitor if ti drives the TCXO?

Would you recommend using both 100nF on TCX0 and 47nF on DCPL_XOSC?

Only the 47 nF should be connected to DCPL_XOSC in addition to the TCXO. This is to keep the LDO stable.

Sorry to bother, I come back on this topic, but I need to get consolidated data on this point.

I aim to supply a TCXO (1,8V 2mA max consomption) with this DCPL_XOSC output.

My supply is 3V3 5%, so I will never get anyhwere near 2V.

With such conditions, do you garantee that DCPL_XOSC will supply 1V8 2mA on all operating temperature?

With such headroom, PSSR shall be good, so there shall be no noise on supply

Would you have additional information on this?

Is DCPL_XOSC build to supply external TCXO as Design reference suggest? Is that more dedicated to internal logic for external quartz?

Is the Design Reference validated on all temperature range?

If you got any additional data that could help, I'd be grateful.

Thanks.

BR

Hi,

Back again on this issue...

I need now to supply a TCXO 1V8 2mA max with DCPL_XOSC.

My min supply would be 2.2V.

Would DCPL_XOSC be able to supply the TCXO on all T° range ( -40°C, +85°C).

Would it only be a matter of noise because of not enough head room?

THX