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OPT3101: OPT3101 reduce power consumption / switch modes

Ben Jansen
Prodigy 20 points
Part Number: OPT3101

Hello,

We are looking for ways to reduce power consumption for a battery operated OPT3101 design. My understanding is that  there is

a) the main OPT3101 unit which consumes power and

b) the emitter LED which consumes power

Of these the LED will consume most of the power apparently. Basic idea is that the module power consumption should be as low as possible until an (external) event happens. Then it should start continuous measurement until another external trigger where it should go to the low power mode.

One solution could be that the OPT is in single shot mode so deep sleep. So LED is switched off as well. Periodically we send a trigger to do a single measurement. Maybe 5 Hz. I understand this would mean that the OPT and the LED are only active briefly and reduce power consumption. Kind of low duty cycle. Most part of the time the system would sleep.

Other solution would be that the system gets an external trigger and starts continuous measurement until another trigger stops it. In this case the OPT  doesn't need to be in deep sleep but maybe could be switched off completely or in a kind of standby.

another solution is just switch LED on when starting continuous measuring and off when not measuring. Does this happen automatically?

questions: can you switch actively between single shot and continuous mode by just setting the register. No resetting needed? if so what would the timing be? switching from single shot to continuous?  Waking from deep sleep to single shot timing is given but nothing else.

If not possible to switch actively during operation?  How do I disable and enable the LED drivers so it is not drawing current. (Bit 0 from register 79?  The naming is not consequent in the datasheet.)  And perhaps reduce power draw from OPT3101 as well. Or stop measurement alltogether and that it switches off LED as well until starting measuring again?  Does it have a kind of  standby mode?

And lastly, how fast does the OPT3101 boot during startup (or a reset. Is a quick reset possible?) Every few seconds starting OPT when external trigger activates it and after a minute switching off when another external trigger happens. The time between powering up OPT module and starting continuous measurement should be no more than 20 mS or so.

thanks!

Ben

  • 0
    TI__Expert 6800 points

    Hi Ben,

    Let me go over this and I'll have a response for you tomorrow.

    Thank you,

    Brent Elliott

  • 0
    TI__Expert 6800 points

    Hi Ben,

    You can change from monoshot to continuous mode from standby mode (enabling timing generator TG_EN=1) without having to reset anything. I am not aware of any timing specifications for switching between these modes. The timing of the OPT3101 boot will ultimately be limited by the speed at which the device loads the registers from the external EEPROM. This would need to be tested since I don't have data on that. 

    The device will not enter a deep sleep mode when taken out of continuous mode, but only after capturing while in monoshot mode. When in standby mode, the reference, oscillator, and ambient cancellation are still active. Because of this, the simplest solution would be to use monoshot mode for the distance measurements since power is a large concern for this.

    Thank you,

    Brent Elliott

  • 0 in reply to Brent Elliott
    Prodigy 20 points

    Hi Brent, thanks for your answer. Really helpfull!!!  A few questions:

    1) So if I understand correctly the best thing to do is simply staying in monoshot mode and start triggiering monoshot measurements fast enough when necessary

     System in one shot mode and deep sleep. When an event happens external trigger system starts up and start sending trigger pulses to OPT. OPT awakes from deep sleep and starts first measurement. Between triggers OPT goes into deep sleep. Would 100hz be possible?  After event finishes external triggerring stops and OPTR goes into deep sleep.

    Sound OK to me but only if about 100Hz single shot would be possible. From datasheet I understand this should be possible as wake up from standby is fast enough at 0.4 mS. Don't know how long it takes to go into deep sleep but expect it won't be much longer.

    2) Is it possible to switch to continuous back from monoshot by disabling timing generator TG_EN=0?

    3) How do I disable and enable the LED drivers so it is not drawing current. (Bit 0 from register 79?  The naming seems not consequent in the datasheet.

    regards,

    Ben

  • 0 in reply to Ben Jansen
    TI__Expert 6800 points

    Hi Ben,

    1. Yes, that would be my suggestion. 100 Hz is possible. The device works by taking a certain number of subframes (each subframe is taken at 4 kHz), and then computing the distance based on the data from those subframes. If you want to have 100 separate measurements from the device per second, you will lose a lot of time due to the device going to sleep, waking up, and I2C transactions. The measurement of however many samples you get in that time will more than likely be less accurate than if you had a single monoshot with an amount of subframes that takes the same amount of time, since you will eliminate all of those wakes and sleeps.

    2. It actually might not be possible to switch back from continuous to monoshot without resetting the device. This would need to be tested.

    3.  Register 76 can be used to disable powerdown of blocks when in deep sleep mode, but by default all of these blocks will shut down during sleep mode, including the illumination driver.

    Thank you,

    Brent Elliott

  • 0 in reply to Brent Elliott
    Prodigy 20 points

    Hi Brent,

    so if I understand correctly under case1) you are saying that I could do a monoshot of 1 second (many subframes) and it would be more precise than 100 fast monoshots and averaging them? Is this what you are saying?

    In my case I simply need 50 to 100 Hz sampling to accurately measure a fast change in distance so slow sampling once a second is no option. About once every minute our device needs to sample at about 100Hz for about 30 seconds. And then again wait for a minute. Times may vary. Depends on external signal. And I need to save power because battery operated. Hence the idea of switching between monoshot where OPT can go to deep sleep and switching back to continuous for doing 30s of measurements at 100Hz. As it's not clear if I can switch back and forth between monoshot (where I can use deep sleep) and continuous mode I liked your idea of doing 100Hz monoshot pulses. But only if they are accurate enough

    But how is doing 100Hz monoshots different from 100Hz continuous? With continuous the OPT is taking 10mS per sample and more subframes than 100Hz monoshot where each sample takes perhaps 2mS and the rest deep sleep. So I should take as many subframes as possible with each sample of 100Hz monoshot so that each sample including startup and stop takes almost 10mS. That would be more accurate but consume more energy as well. But when not in 100Hz mode the OPtTwould deep sleep. 

    Until now we tested with an available example for the OPT (TF luna) library so haven't changed any subframe setting or anything. Just checked the default example to see if accuracy and distance were what we are looking for. So skipped a bit the datasheet part of subframes. Now looking into actual energy saving. And your suggestion of 100Hz monoshot. And so question of accuracy pops up. Will do some testing if I can change subframe etc and also if switching between monoshot and continuous and vice versa is possible

    Just one more question: Can I switch off / on illumination driver when in continuous mode?

    thanks,

    Ben

    edit: checked out datasheet subframing. All quite clear now.

  • 0 in reply to Ben Jansen
    TI__Expert 6800 points

    Hi Ben,

    From your edit are you clear with just subframing or is there anything else that needs clearing up? Let me know if so.

    Thank you,

    Brent Elliott