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Looking for a small-size, small-output, PWM-enabled LED driver

Anonymous
Anonymous
Guru 17045 points
Other Parts Discussed in Thread: TPS60230, TPS61150, TPS61150A, TPS61183, LM3407, TPS75105, TPS75103, TPS60231

Hello,

 

We are looking for a small footprint, cheap, yet PWM dimming control enabled LED driver. Some more specific requirements are below:

  1. Output: 1 to 2 channels. For each channel we would have one, at most two ordinary small white LEDs connected in series, with working voltage 3.0-3.3V
  2. Current per channel: no greater than 30mA
  3. PWM dimming: required

 

Does TI have any suitable driver in the portfolio?

 

Garry Hodges

 

  • What is the input voltage?

  • Anonymous
    0 Anonymous in reply to Jeff F

    Jeff,

    It's between 2.8 to 3V.

     

    Garry

  • If you only have 1 LED per string, then I suggest the TPS60230, tying two strings together to get 30mA.

    If you have 2 LEDs per string and only 2 strings, then I suggest the TPS61150. 

     

     

  • Gary,

    What I didn't see in your request was input supply voltage, so I will list a few alternatives which can support multi-strings in the same IC.

     

    Boost:

    • TPS61150A - Dual Output Boost WLED driver (single inductor)
    • TPS61183 - 6 channel 

    Buck

    • LM3407 - floating buck for single string.

    Linear

    • LM3432 / LM3432B - 6-channel Linear LED driver
    • TPS95105 - 4-channel linear LED driver.  

     

    Regards,

    John

  • Anonymous
    0 Anonymous in reply to John Perry

    John,

     

     

    Would TPS75105 be an option?

    Garry

  • For the TPS75103 to work, its input voltage would need to be a dropout voltage higher than the highest output voltage, or Vin(min) = VLEDmax+Vdropout.

  • Anonymous
    0 Anonymous in reply to Jeff F

    Jeff,

     

    I am interested in TPS60230. However, according to the datasheet this is a fractional charge pump with 1x/1.5x modes. It therefore seems to me that it behaves like a "step-up" converter with Vout/Vin either 1.0 or 1.5.

     Contradicting this, datasheet page 3 lists input voltage range as [2.7, 6.5] (see image below). But LEDs usually have a fixed forward voltage which is not supposed to be exceeded. For instance, if VForward is 3.3V and there is no additional resistor connected in series with LED, does 1x/1.5x mean VIN must be either 3.3V (3.3/1) or 2.2V(3.3/1.5)?

     

     

    On the other hand, I read somewhere that "Regulated Charge Pump" is a combination of fractional charge pump and a feedback control (see image above). So is TPS60230 a fractional charge pump only, or is in fact a "Regulated Charge Pump" with additional feedback control circuits?

     

    Garry Hodges

  • The TPS60230's feedback loop ensures that the fractional charge pump provides only enough output power to keep the Dx pin voltages high enough for operation.   The voltage at the VOUT is not regulated but will be the sum of the LED voltage, created by the current being pulled through it, and the minimum voltage required by the Dx pins. 

  • Anonymous
    0 Anonymous in reply to Jeff F

    Jeff,

    So may I understand as: Because of the presence of the feedback, the input voltage can vary between 2.7V and 6.5V, while the output current would still be current?

     

    Garry

  • Yes.  The LED current will be regulated.  At max Vin, the charge pump will not be very efficient because it will be acting more a linear regulator and stepping down the input voltage instead boosting.

  • Anonymous
    0 Anonymous in reply to Jeff F

    Jeff,

    First,

    For TPS60230,

    1. It is  LED driver, but not listed under Power Management > Lighting and Display Solutions.

    2. It is only listed under Power Management > Switching Regulator > Inductorless DC/DC Regulator (Charge Pump) > Step-Up Charge Pump Regulator.

    I found this classification scheme has the disadvantage that:

    Some LED drivers (e.g. TPS60230) are not listed under (1), so by using the selection tool the customer could miss them

    Does there exist a more complete/comprehensive tool listing all LED drivers without missing any?

    Second,

    I am using only two LEDs

    • Input voltage range:                 3.0-3.3V
    • Maximum forward voltage:     3.3V
    • Maximum current:                    25mA
    • Series or parallel:                    either
    • PWM dimming control:           required

     

    I found that TPS60230 has up to 5 LED Vout pins which is probably too redundant. Is there a driver of smaller size and still satisfying the above requirements?

     

    Garry

  • I apologize for the confusion.  Regarding 1, we shifted our focus aware from ICs that backlight smaller displays, such as found in cell phones.  So, the marketing collateral leaves those out. Regarding 2, the TPS60231 should be there but it should also be searchable with over WLED drivers.  With incorporating the former National Semi parts into our search, the TPS60230/1 got dropped.  I will get that fixed.

    For your application, I still recommend the TPS60231, which is the 3 string version of the TPS60230. 

     

     

  • Anonymous
    0 Anonymous in reply to Jeff F

    Jeff,

    I was looking for TPS60230 and TPS60231 PCB foorprint; but the webpage seems only provide schematic symbol for download?

    Could you provide TPS60231 footprint?

     

    Garry

  • Anonymous
    0 Anonymous in reply to Jeff F

    Jeff,

    With either 60230 or 60231, would there be ripple in the LED current due to Vin change?

     

    Garry

  • The footprint is toward the back of the datasheet. 

    The switching noise is at such a high frequency and so small that human eye cannot detect changes in the LED brightness.