• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 64 subscribers
  • Views 714 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3410X (LM3410XBSTOVPEV) eval board concern/issue

cm
Prodigy 100 points
Other Parts Discussed in Thread: LM3410

having an issue with this board not regulating current properly.  to prevent damage we tested as follows limiting current from power supply.

test observations:
we've modified this board to drive LEDs other than on-board ones (cut trace between board LEDs and ground, added wires to go off-board).  the DIMM signal is tied to V-in through a 100 kOhm resistor.  V-in is set to 5.0 V and current limit on power supply is set to zero.  monitoring LED current and V-FB (and they track each other as they should with 1 ohm resistor on board).  R4 not installed.

upon increasing current limit on power supply, current will begin to flow and LED lights up and power supply voltage shows 2.0-2.1 V output.  further increase on current limit causes LED current to increase toward limit (190 mA) with no change in output voltage (2 V).  as we approach 190 mA LED current the current will suddenly increase to 350-400 mA (didn't let it run long) and nearly full V-in of 5 V.

Questions:
1-don't understand why current is not being regulated to 190 mA as this is purpose of the device.  suggestions?
2-are there any other tests which would help explain this behavior?
3-what other ways can we make the board function as needed, other than putting PWM on DIMM pin (which would be a PITA).

thanks

  • 0
    Prodigy 100 points

    other detail:
    using the on-board set of 4 LEDs the circuit regulates at 190 mA as designed.  the loss of regulation occurs when instead it drives a single 200 mA (green) LED.  i haven't found it in the data sheets yet but maybe the problem is driving a LED whose turn-on voltage is below some lower threshold?  

  • 0 in reply to cm
    TI__Mastermind 25500 points
    The LM3410 is a boost regulator. The output voltage must be higher than the input voltage for regulation, otherwise there is a direct path between the input through the inductor and diode through the LED and you can have overcurrent (the boost regulator will not even be switching). If you have a single LED with a 5V input you will need either a buck or a buck-boost regulator to achieve regulation.
  • 0 in reply to Clinton Jensen
    Prodigy 100 points
    thanks Clinton- after i thought about it (and added series LEDs to verify) it seemed clear output voltage needed to be higher. interesting (a little), and verifying your explanation, was 2 LEDs allowed the board to regulate properly but with DIMM=0 there was about 0.5 mA of current to faintly turn on the LEDs. with 3 LEDs there was no current with DIMM=0 and proper regulation.
    thanks for your answer.