LPC804 - external 32Khz clock source

[shai_b]

Hello Team,

My customer is planning to use LPC804 in a smart low power tag, they need to use an external clock to achieved high accuracy clock source.

Please advise if our LPC804 can works with 32.768Khz crystal if not what is the minimum clock frequency as CLK_IN the LPC80x supports that suit for lowest power consumption mode, Thanks in advance 

Kind regards,

Shai 

[Sabina_Bruce]

Hello Shai,

Hope you are doing well.

For the lpc804 you will not be able to use a crystal, the clkin pin may accept an external clock source. However in order to choose the minimum you will have to review the tables 12 and 18 of the datasheet to match your application. The maximum frequency is 15MHz.

Best Regards,

Sabina

-----------------------------------------------------------------------------------------------------------------------

Note: If this post answers your question, please click the Correct Answer button. Thank you!

----------------------------------------------------------------------------------------------------------------------- 

[shai_b]

Sabina,

Thanks for your inputs, according to the Datasheet in table 12 I've noticed there is mentioned of 1Mhz crystal which can lead the lowest power consumption in active mode but there is not 1Mhz crystal mentioned in sleep mode.

Could you please advise which kind of crystal is recommend to achieve the lowest power consumption (in sleep and active mode)? Thanks in advance.

just to remind you the application is smart-tag and there is a requirement for ultra-low power and high accuracy in terms of cunting time (using an external crystal for reaching  +-1ppm error rate)  

I will appreciate your suggestion here.

Thanks and regards,

Shai

[Sabina_Bruce]

Hello Shai,

Hope you are doing well.

The datasheet does not specify the use of a crystal. As mentioned, it will not be possible to use an external crystal with the LPC804. The datasheet on table 12 describes the different FRO frequencies(internal oscillator), in addition for the active more the FRO is disabled and the internal low power oscillator is enabled which has a fixed output of 1 MHz.

I recommend that you try the example that lets you test the different power modes from the SDK (LPCXpresso804_power_mode_switch_lpc), you may vary the clock source using the config tool in MCUXpresso IDE for quick testing and will be able to determine the best option for your application. Please keep in mind that the datasheet specifies typical values and with all GPIO outputs driven LOW and pull-up resistors disabled. This means that the results on your end will vary.

Best Regards,

Sabina

-----------------------------------------------------------------------------------------------------------------------

Note: If this post answers your question, please click the Correct Answer button. Thank you!

----------------------------------------------------------------------------------------------------------------------- 

[shai_b]

Sabina, Thank you for your inputs.

Kind regards,

Shai