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LP8860-Q1: current sink function

T Kishi
Genius 4425 points
Part Number: LP8860-Q1

Hi

My Customer has question.

Can I use only the current sink function without using the Boost function of LP 8860-Q1?

The simple configuration is as attached.

LP8860_1.pdf

Best Regard

T Kishi

  • 0
    TI__Expert 5475 points
    Hi,

    We have not seen any customer using the device like that. May I ask what is their application? Why do they need so many RGB LED strings? The typical application is for backlighting with white LEDs.
    I think the connection should be ok if they can connect properly to make sure there is no unwanted fault triggered. For example, for the device #2 and #3 which have no boost, connect VSENSE_P and VSENSE_N together. Connect FB to the boost output of device #1.
    Besides that, another thing that is needed to considered is the thermal. For device #2 and #3, adaptive headroom control will be inactive. Then the voltage drop on the current sink will be high. Make sure the thermal is within limit.
  • 0 in reply to Shirley He
    Intellectual 390 points

    Hi, Shirley,

    This is *almost* the application I want to ask about. I want to use one LP8860-Q1 without any boost power supply:

    The application is to control a set of LEDs (4 strings of 3 diodes each), using only the precision current sinks ( 0 to <65mA), with a fixed (~12VDC) power supply.

    No external PWM, just SPI or I2C.

    If my circuit leaves out all of the boost topology parts, what do I need to do to operate the LP8860?

    * Supply 12VDC at Vdd

    * Connect VSENSE_P to VSENSE_N

    * Connect FB to +12V ??

    Can I leave out C2x and Ccpump ?

    What about Isense and Isense_gnd ?

    Anything else to worry about?

    Initially, what do you recommend I do to test this all out using an LP8860-Q1EVM eval board?

    Thank you!

    Dave

  • 0 in reply to Dave Bell1
    TI__Expert 5475 points
    Hi Dave,

    Below are some aspects I can think out to use LP8860 without using a boost. We have not used the device in this way, so we're not sure if it is workable.

    * Supply 12VDC at Vdd

    * Connect VSENSE_P to VSENSE_N

    * Connect FB to +12V ??
    I think it should be ok.

    Can I leave out C2x and Ccpump ?
    Be sure to disable the charge pump.

    What about Isense and Isense_gnd ?
    Connect ISENSE to ground.

    Anything else to worry about?
    Be sure to disable all the fault detections of the boost or make sure the faults cannot be triggered.
  • 0 in reply to Shirley He
    Intellectual 390 points

    Thank you, Shirley!

    To make sure I understand correctly,

    What about Isense and Isense_gnd ?
    Connect ISENSE to ground.

    Connect both Isense and Isense_gnd pins to power/analog ground?

    Can I leave out C2x and Ccpump ?
    Be sure to disable the charge pump.

    Is there an Enable/Disable pin I missed, or do I disable via SPI/I2C?

    Be sure to disable all the fault detections of the boost or make sure the faults cannot be triggered.

    Similarly, via SPI/I2C, or ae there hardware Disables?

    Dave

  • 0 in reply to Dave Bell1
    TI__Expert 5475 points
    Hi Dave,

    Please disable the charge pump, other fault detections, and disable boost adaptive mode via SPI/I2C.