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TPS62200 LED Driver

Juval Izhaki
Prodigy 70 points
Other Parts Discussed in Thread: TPS62200, TPS62120, TPS62110, TPS75103, TPS62240, TPS62260, TPS61260

Hi

I would like to use the TPS62200 sync buck regulator as a low current LED (the LED only consume 4v@20mA from a 6V battery source) driver in a current feedback form.

My question is as follow :

1. Can the TPS62200 be used as a led driver?

2. Can I dim the LED by PWM modulating the EN input?

3. Would this type of design considered efficient design?

4. What is the efficiency of this type of circuit and how to calculate it?

 

Thanks

Yuval

 

 

 

 

  • 0
    TI__Guru*** 142860 points

    Just 1 LED?  What is your battery voltage range?  i.e. 4 AA can go up to around 6.5V when fresh.

    If you have a 5V rail in your system, the TPS75103 would be perfect.  If your Vin goes higher than 6V, then you will need to use the TPS62120.  The TPS62110 has an EVM that shows an example of how to drive an LED with these parts.

    The TPS62200 had not been tested as an LED driver.  It may work but there are newer, smaller solutions available.

    If the IC is not an LED driver and does not contain a dedicated pin for PWM dimming, then typically you can toggle the EN pin to get PWM dimming.  The typical frequency is around 100 Hz in this case.

    At your low currents and relatively high Vf, either a linear or switching driver would be efficient.  You can consider the LED as your load and thus output power is equal to Vf * Iled.

    What else do you have in your system?  Likely, this LED is not determining the overall system efficiency.

  • 0 in reply to Chris Glaser
    Prodigy 70 points

    Hi Chris 

    Thank you for the fast answer.

    I have decided to switched from the TPS62200 to TPS62240 due to budget limitation (the 62240 cost less)

    I have found on the net an application note describing a LED driver for the TPS62260 who is the same as TPS62240 only designed for 600mA.

    Any how my design work  from 2 x CR2032 3V lithium battery and controlled by an MSP430 micro controller.

    The LED's connected in series and  consume 20mA ,the LED need's a minimum of 4V for normal operation.

    PWM is only needed for soft-starting the device.

    I have design the system for high efficiency - in power off mode the system should consume less then 10uA (basically i disconnect the micro from the power path and putting the TPS62240 and the LDO (TPS76330) to sleep using the enable(EN) pin's

    Thanks

    Yuval

  • 0 in reply to Juval Izhaki
    TI__Guru*** 142860 points

    Yes, if your 3V battery is really 3V maximum even when fresh, then the TPS62240 solution per that app note is perfect.

    If you wanted to only use 1 coin cell, you could use a boost converter such as the TPS61260.

    The TPS62240 and TPS76330's shutdown currents are in the datasheet and are much less than 10uA.  Why do you use the TPS76330?  We have many newer linear regulators that give better performance and lower cost.

  • 0 in reply to Chris Glaser
    Prodigy 70 points

    Hi Chris

    Thanks for the answer.

    I decide to use the TPS76330 because I am familiar with it.

    Can you recommend a better chip with foot print like SOT23-5, shut down pin ,lower cost and very lo IQ?

    Yuval

     

     

  • 0 in reply to Juval Izhaki
    TI__Guru*** 142860 points

    Yes.  You can find one that meets your specs at power.ti.com.  I would check out our TLV7 series, which are super low cost LDOs.

    The TPS76330 is an old part with relatively high Iq (85 uA) and it requires a large, costly tantalum output cap.  Newer LDOs have Iq around 40 uA or even 1uA and require cheaper ceramics.

    The TLV70430 looks to meet your needs.

  • 0 in reply to Chris Glaser
    Prodigy 70 points

    Hi Chris

    Thanks for the replay.

    I have check the TLV70033 it looks good but it works up to 5.5V (absolute max is 6V) my system works with two 3V battery (6V) I am not sure whether it is a good solution to make the system work near the regulator absolut max value.

    I thought of adding a diode in series with the regulator VIN rail (this way I can keep the low price and stay away from the absolute max VIN region)?

    Yuval

     

  • 0 in reply to Juval Izhaki
    TI__Guru*** 142860 points

    I would highly recommend staying within the recommended operating conditions.  You must stay within the absolute maximum operating conditions.

    A diode works if it can guarantee that enough voltage drop.  Here is an app note that discusses other ways: http://www.ti.com/lit/an/slva119/slva119.pdf

    You can search for a higher input voltage LDO with the power quick search at power.ti.com.  The TLV70430 that I recommended will work.