LPC845 Low-power oscillator temperature

[1234567890]

Datasheet says low-power oscillator frequency is +-40 % over process and temperature. May drift while counting due to temperature changes.

=> Are there any documents available specifying the influence of _just_ the temperature? Measuring/Calibration at a specific temperature is not that difficult. But how strong will the temperature change the frequency? 1 % per 30K? 5 % per 30K? 10 % per 30K? ...

VDD will have influence as well (but under my control); actually I'm interested only in temperature.

[ZhangJennie]

HI

LPO is designed for low power wake up,  they don't need high precision clock. Thus besides +-40% precision, we don't have its spec for temperature variation.

could you pls describe what you want this LPO for? will it be used for waking up the device only? or is that used for communication with external device? why you need this spec?

Have a great day,
Jun Zhang

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[1234567890]

Hi.

I will need (actual plan...) the LPO on a battery powered radio device as a transmitter, for waking up (from deep power down or maybe power down) only. To reduce power consumption on the receiver side as well I want to activate the receiver only shortly before the transmitter starts to send. So they need a kind of time synchronisation to be only active at the very same time. The receiver will send back a time stamp to the sender so the sender know the time deviation to the receiver (just possible for relatively small deviations, of course). With this information and the actual (temperature dependent) LPO frequency the sender can calculate the value for COUNT->VALUE for the next sending point to wake up.

This only can work when the influence of the temperaure (-> LPO frequency) isn't too big. With indoor nodes (pretty stable temperatures) no problem, but a few outdoor nodes are an option at the moment. And there can be easiliy more then 10 K difference in an hour or so.

So I have to make a few simple measurements by myself.

Thanks.

[ZhangJennie]

HI

Thanks for the sharing.

Just FYI, If you need accurate clock source. external clock is recommended.

The WKT can use a clock input on the external pin PIO0_28 for clocking the wake-up timer in sleep, deep-sleep, power-down, and deep power-down modes. Select the external clock source by setting bit SET_EXTCLK in the CTRL register.

For more information, see user manual, Chapter 23: LPC84x Self-wake-up timer (WKT)

Have a great day,
Jun Zhang

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