Disconnection after a voltage drop

RE: Disconnection after a voltage drop

AmbystomaLabs — Mon, 17 Dec 2018 13:21:09 GMT

How big of a capacitor do you have?

According to what you wrote above, the buzzer uses 80mA and operates for 1 sec. Assuming that the nRF is using a modicum of current compared to your buzzer. The capacitor would need to be i=Cdv/dt

(0.080A / 0.5V (voltage drop) x 1sec) equals 0.16Farads or 160,000uF.

RE: Disconnection after a voltage drop

bjorn-spockeli — Mon, 17 Dec 2018 12:54:50 GMT

Could you provide a plot of VDD of the nRF51822 during an active connection when the buzzer is turned on?

As long as VDD is within the recommended operating conditions stated in the PS(see below), then you should not see the connection drop.

Symbol Parameter Notes Min. Typ. Max. Units
VDD Supply voltage, internal LDO setup 1.8 3.0 3.6 V
VDD Supply voltage, DC/DC converter setup 2.1 3.0 3.6 V
VDD Supply voltage, low voltage mode 1.75 1.8 1.95 V

RE: Disconnection after a voltage drop

far987 — Mon, 17 Dec 2018 12:03:41 GMT

Thanks for your reply.
we use a capacitor to supply this amount of current.
I understand this voltage drop, but we have always enough voltage to keep nrf51822 and buzzer ON.
As I mentioned, the buzzer keeps beeping even after disconnection.

Is there any solution to maximize connection probability? I mean stay connected on the worst case of voltage drop. is there any predefined minimum threshold of voltage to stay connected ?

RE: Disconnection after a voltage drop

AmbystomaLabs — Thu, 13 Dec 2018 18:40:57 GMT

You should review the content on CR batteries. Just search in the devzone you will find a lot. Also there is a Nordic whitepaper on the subject.

This is a wholly inappropriate application for a CR battery. Lithium manganese button cells cannot supply that much current.

A CR2032 is rated for 0.2mA continuous load and according to the panasonic spec has a pulsed rating of 3.3mA. The folks at Energizer show a pulsed rating of 6.8mA.

If you monitor the voltage with an O-scope during radio operation I'm sure you will see it dropping significantly below 2.5v.