Questions about I/O ,crystal of nRF51822

[Alice]

Hi

I want to use the nRF51822 to do the BLE product.I have read the datasheet of nRF51822.I have some questions:

1、Can the I/O of nRF51822 support 4.5V~5V input? 2、Can nRF51822 use the active oscillator?I think it is more stable than passive crysta. 3、For the power mode,if I have done as "nRF51822 QFN48 schematic with internal DC/DC converter",however,when the DC/DC is disable,is 51822 works in the LDO mode?

Look forward to your reply.Thank you very much.

King regards, Alice

[Håkon Alseth]

Hi Alice,

1. The GPIO on nRF51822 can not handle more than VDD+0.3V. Example: If you're running on 3.3V, the maximum voltage on a GPIO is 3.6V.

If you use it purely as a input, I would suggest using a resistor divider. If output, use a transistor buffer. If bidirectional, then you will have to use a level shifter.

2. Yes, you can source the nRF-device from an active crystal. This is done by connecting it to pin "XC1" and leaving XC2 unconnected.

3. Yes, it will then fallback to LDO operation. However, I would strongly recommend that you read Stefan's post in this thread before designing in the DCDC: devzone.nordicsemi.com/.../ldo-vs-dcdc-nrf51822

Best regards Håkon