Can STM32L071KZU6 use HSE oscillator?

[Aaron G]

Posted on May 02, 2018 at 14:29

The STM32L071KZU6 is a fairly new part in a compact no-lead (UFQFPN32) package.  I am trying to determine if a high-speed external oscillator can be used with this part (in bypass), but the documentation is inconsistent and unclear.

Arguments for being able to use a high-speed oscillator with STM32L071KZU6:

• Table 2 in the datasheet shows 'Clocks: HSE/LSE/HSI/MSI/LSI' as '1/1/1/1/1' for all parts and packages, including this one, which strongly implies that one HSE is available.
• In the reference manual, section 7.2.1 (HSE Clock), for HSE bypass, it says: 'In this mode, an external clock source must be provided.  It can have a frequency of up to 32MHz...On devices where OSC_IN and OSC_OUT pins are available: the OSC_IN pin must be driven...Otherwise, the CK_IN pin must be driven.'  This implies that there is always an HSE input, but it may be called 'OSC_IN' or 'CK_IN'.

Arguments against being able to use a high-speed oscillator with STM32L0717KZU6:

• The package pinout diagram (Figure 10) in the datasheet shows pin 1 as 'PC14-OSC_IN' and pin 2 as 'PC15-OSC32_OUT'.  There is no 'OSC32_IN' to match 'OSC32_OUT' so it is not clear whether the marking for PC14 is correct.
• Table 15 in the datasheet describes pin 1 for the UFQFPN32 package as 'PC14-OSC32_IN (PC14)' with additional function of 'OSC32_IN'.  There is no pin shown on this package for 'OSC_IN' which is where I would expect the HSE to connect.  'OSC32_' has always meant the 32.768kHz (LSE) clock input on STM32 parts.
• The datasheet shows no pin marked 'CK_IN' as mentioned in the reference manual.  'CK_IN' does not appear anywhere in the datasheet.
• In other STM32 parts, PC14 has always been tied to 'OSC32_IN'. It isn't clear if the role of PC14 has changed just for this package.  Also, Figure 1 in the datasheet shows that the OSC32_IN only goes to the LSE input and OSC_IN only goes to the HSE input, so it does not appear that one pin can do both roles.

So which is it?  Can the STM32L071KZU6 use an external high-speed (20MHz) oscillator in HSE bypass mode or not?  My guess is that it cannot, but I would like to be sure since this this is how we would prefer to use the part.

Can anyone from ST, or anyone who has used this part in this way, provide some clarification?  It would be nice if the documentation made this more explicit.

Thanks.

#STM32L071KZ #UFQFPN32 #HSE

[Aaron G]

Posted on May 02, 2018 at 15:21

As another datapoint, the STM32CubeMX utility does not show HSE as an option in the clock configuration tab for the UFQFPN32 package while it does appear on the QFP100 package for the STM32L071xxx.  This suggests that someone at  ST has looked at this and explicitly removed the HSE from the smaller package in the tool.

I'm going to assume that HSE is not available on this part unless someone has evidence to the contrary.

[Tesla DeLorean]

Posted on May 02, 2018 at 16:46

Pretty sure it is one of the things you give up on the low pin count devices. Consider the smaller WLCSP49 device which does have OSC_IN/OSC_OUT

STM32L072CZY6TR WLCSP49

@ST The docs also make reference to a non-existent 'OSCI_IN' pin

http://www.st.com/content/ccc/resource/technical/document/datasheet/b5/24/80/11/51/59/47/f7/DM00141pdf/files/DM00141pdf/jcr:content/translations/en.DM00141pdf

[waclawek.jan]

Posted on May 03, 2018 at 00:40

Appears HSE is not available in the smallest packages, similarly to other 'L0x.

This is a

https://community.st.com/0D50X00009XkfIfSAJ

here ever since the 'L0 appeared; shame that the DS is not clear in this (and even contains the 1/1/1/1, which is clearly an error - similar to the 'PC14-OSC_IN' mentioned in that 3 years old post too).

JW