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Freedom_Neo
Senior
March 30, 2022
Solved

Why do we choose LSE capacitance low?

STM32H7B3I-DK - Discovery kit use NX3215SA-32.768KHZ-EXS00A-MU00525 Crystal. Crystal Load Capacitance is 6, 9, 12.5 pF but STM32H7B3I-DK - Discovery kit use 1.5pF. Why it use different load capacitance.

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Freedom_Neo
Freedom_NeoBest answer
Senior
March 30, 2022

First, you must be sure that your crystal is compatible with the selected STM32 LSE. Then, it is highly recommended to use a crystal with low pullability, that is with CL ≥ 6 pF:

7 pF is a good compromise between low drift and moderate power consumption

9 and 12.5 pF can be used in noisy environments, but impact the power consumption.

6 replies

Piranha
Principal III
March 30, 2022

> Read AN2867.

Which part of this sentence from the previous topic you do not understand?

Freedom_Neo
Freedom_NeoAuthorBest answer
Senior
March 30, 2022

First, you must be sure that your crystal is compatible with the selected STM32 LSE. Then, it is highly recommended to use a crystal with low pullability, that is with CL ≥ 6 pF:

7 pF is a good compromise between low drift and moderate power consumption

9 and 12.5 pF can be used in noisy environments, but impact the power consumption.

Piranha
Principal III
March 30, 2022

That quote doesn't even answer your question about the capacitors.

I'll tell you a secret - to understand a load capacitance, you should at least read the section called "Load capacitance"!