ANT Forum

I'm looking for some confirmation on what this chip uses for current when a channel has been opened and ANT is immediately put to sleep. This is what I believe to be the IDLE state. I'm seeing a number like 160uA. That is when not sending any data. A 1Hz transmit uses about 200uA.

Minor details:
-Asynchronous 57kbps
-Single bi directional transmit channel
-full use of sleep pin

The ANT power estimator says I should get 55uA when transmitting at 1Hz.

If I put ANT to sleep without an active channel, I see < 2uA with an MCU in power save and <1 in power down. I have no problem with that. But I thought this chip should be about 1uA when in idle state and this is also what I believe the calculator refers to as base current... and I assume that means an open channel.

If there's any tricks to this, I'd like to know. Right now, it uses about 4x the amount of current than I expect.      

Have you had a look at the "Power States" application note? That provides a better description of what the different power states mean.
http://www.thisisant.com/pages/developer-zone/ant-application-notes

Could you please describe the sequence that you are using to "open a channel and put ANT immediately to sleep"? Using the SLEEP line you will avoid consuming power for the serial port when you don't need to send serial messages, but there will still be RF activity as long as the channel is open.      

I'm on a different line of thought for a moment. This is an ANT+ implementation and the device profile dictates a 4Hz channel period. Does ANT continue to send at 4Hz even though I only wake it and send data at 1Hz? That would clear things up. If so, ignore the rest.

If not, here's more detail.

A re-read of the power states cleared up "base current" for me. I configure the channel settings and open the channel using command (0x4C). I wait for RTS to be de-asserted between all commands used for configuration of the channel. I do have successful communication with my slave device (Garmin cycling computer).

Upon opening the channel, I raise the SLEEP line. I have waited up to 5 seconds also, just to make sure unknown things have had a chance to settle. This procedure is to test power consumption without communication because I intend to use the SLEEP state a lot.

This design does have a 32kHz crystal.      

If you open a master channel at 4Hz, it *will* transmit every 250ms. When you send data to ANT, you are only updating the contents of the broadcast buffer.

Also note that because you are working with an ANT+ sensor implementation, you must use the channel period specified in the profile, as using a lower rate would cause interoperability issues with other receivers.      

Thanks for the clarification, alejandra. I have discovered that I can use exact multiples of the device profile's period and synchronization will be maintained and the predicted power savings are realized. Quite interesting, if not in strict adherence to the spec.