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Original question:

LP5036: Are there internal protection diodes around OUTx ?

LP5036: Excessive leakage

Derek
Mastermind 9792 points
Part Number: LP5036
Other Parts Discussed in Thread: LP5030, LP5024

Hello,

   I'm working on a medical device that we are trying to expedite into the market for obvious reasons. We're having a problem with multiple boards and I need your help.

The LP5036 is connected to ten (10) RGB LEDs. Each element on the LED gets its own output channel on the LP5036. Yes, we could have used the LP5030 but the LP5036 was more readily available so we are using that for now.

PROBLEM: All red LEDs are on continuously, about 1mA for entire board of 10 red elements. This would be a leakage of about 100uA, far above the specification. This occurs even when the board is totally disconnected from I2C bus; only VLED and VCC are powered.

Riref is set to 10k; 
Each LED is Kingbright APFA3010SEEZGKQBKC, forward voltage is 2V Red, 3.3V Green, 3.3V Blue. Physically the Red pin and Common pin are on opposite sides of the package so
VCC is 3.3V. LEDs are powered by 3 'C' batteries, nominal voltage 4.5V.
Supplying both LVCC and LEDs from 3.3V (as a test) results in current draw of 1.07mA. Much higher than leakage current specified.

Tried turning off CHIP_EN in DEVICE_CONFIG0, no change
Tried turnning of LED_GLOBAL_OFF in DEVICE_CONFIG1, no change
Tried toggling hardware EN pin, no change.
Tried halving the value of Riref (to 5k) but no change.

If it was just a random solder problem then I would have expected the other channels (blue & green) to be affected. I also would have expected to see some channels affected but not all.

LED board using LP5036.pdf

reGISTERS UPON STARTUP:
LP205xx Register Values:
[0] DEVICE_CONFIG0 = 0x00 [1] DEVICE_CONFIG1 = 0x3C [2] LED_CONFIG0 = 0x00 [3] LED_CONFIG1 = 0x00
[4] BANK_BRIGHT = 0xFF [5] BANK_A_COLOR = 0x00 [6] BANK_B_COLOR = 0x00 [7] BANK_C_COLOR = 0x00
[8] LED0_BRIGHT = 0xFF [9] LED1_BRIGHT = 0xFF [10] LED2_BRIGHT = 0xFF [11] LED3_BRIGHT = 0xFF
[12] LED4_BRIGHT = 0xFF [13] LED5_BRIGHT = 0xFF [14] LED6_BRIGHT = 0xFF [15] LED7_BRIGHT = 0xFF
[16] LED8_BRIGHT = 0xFF [17] LED9_BRIGHT = 0xFF [18] LED10_BRIGHT = 0xFF [19] LED11_BRIGHT = 0xFF
[20] OUT0_COLOR = 0x00 [21] OUT1_COLOR = 0x00 [22] OUT2_COLOR = 0x00 [23] OUT3_COLOR = 0x00
[24] OUT4_COLOR = 0x00 [25] OUT5_COLOR = 0x00 [26] OUT6_COLOR = 0x00 [27] OUT7_COLOR = 0x00
[28] OUT8_COLOR = 0x00 [29] OUT9_COLOR = 0x00 [30] OUT10_COLOR = 0x00 [31] OUT11_COLOR = 0x00
[32] OUT12_COLOR = 0x00 [33] OUT13_COLOR = 0x00 [34] OUT14_COLOR = 0x00 [35] OUT15_COLOR = 0x00
[36] OUT16_COLOR = 0x00 [37] OUT17_COLOR = 0x00 [38] OUT18_COLOR = 0x00 [39] OUT19_COLOR = 0x00
[40] OUT20_COLOR = 0x00 [41] OUT21_COLOR = 0x00 [42] OUT22_COLOR = 0x00 [43] OUT23_COLOR = 0x00
[44] OUT24_COLOR = 0x00 [45] OUT25_COLOR = 0x00 [46] OUT26_COLOR = 0x00 [47] OUT27_COLOR = 0x00
[48] OUT28_COLOR = 0x00 [49] OUT29_COLOR = 0x00 [50] OUT30_COLOR = 0x00 [51] OUT31_COLOR = 0x00
[52] OUT32_COLOR = 0x00 [53] OUT33_COLOR = 0x00 [54] OUT34_COLOR = 0x00 [55] OUT35_COLOR = 0x00

AFTER TURNING OFF LED GLOBAL OFF:
issue persists:

LP205xx Register Values:
[0] DEVICE_CONFIG0 = 0x40 [1] DEVICE_CONFIG1 = 0x01 [2] LED_CONFIG0 = 0x00 [3] LED_CONFIG1 = 0x00
[4] BANK_BRIGHT = 0xFF [5] BANK_A_COLOR = 0x00 [6] BANK_B_COLOR = 0x00 [7] BANK_C_COLOR = 0x00
[8] LED0_BRIGHT = 0xFF [9] LED1_BRIGHT = 0xFF [10] LED2_BRIGHT = 0xFF [11] LED3_BRIGHT = 0xFF
[12] LED4_BRIGHT = 0xFF [13] LED5_BRIGHT = 0xFF [14] LED6_BRIGHT = 0xFF [15] LED7_BRIGHT = 0xFF
[16] LED8_BRIGHT = 0xFF [17] LED9_BRIGHT = 0xFF [18] LED10_BRIGHT = 0xFF [19] LED11_BRIGHT = 0xFF
[20] OUT0_COLOR = 0x00 [21] OUT1_COLOR = 0x1F [22] OUT2_COLOR = 0x00 [23] OUT3_COLOR = 0x00
[24] OUT4_COLOR = 0x1F [25] OUT5_COLOR = 0x00 [26] OUT6_COLOR = 0x00 [27] OUT7_COLOR = 0x1F
[28] OUT8_COLOR = 0x00 [29] OUT9_COLOR = 0x00 [30] OUT10_COLOR = 0x1F [31] OUT11_COLOR = 0x00
[32] OUT12_COLOR = 0x00 [33] OUT13_COLOR = 0x1F [34] OUT14_COLOR = 0x00 [35] OUT15_COLOR = 0x00
[36] OUT16_COLOR = 0x1F [37] OUT17_COLOR = 0x00 [38] OUT18_COLOR = 0x00 [39] OUT19_COLOR = 0x1F
[40] OUT20_COLOR = 0x00 [41] OUT21_COLOR = 0x00 [42] OUT22_COLOR = 0x1F [43] OUT23_COLOR = 0x00
[44] OUT24_COLOR = 0x00 [45] OUT25_COLOR = 0x1F [46] OUT26_COLOR = 0x00 [47] OUT27_COLOR = 0x00
[48] OUT28_COLOR = 0x1F [49] OUT29_COLOR = 0x00 [50] OUT30_COLOR = 0x00 [51] OUT31_COLOR = 0x00
[52] OUT32_COLOR = 0x00 [53] OUT33_COLOR = 0x00 [54] OUT34_COLOR = 0x00 [55] OUT35_COLOR = 0x00
[56] RESET = 0x00....(tick)#........(tick)#.

  • 0
    Mastermind 9792 points

    Further testing: I checked all the channels with a current meter, not just the red ones, and even when the device is off, all have a 2.5mA steady leakage current, measuring current from VBAT to OUTx. When VBAT = 3.0V, the output voltage (measured between OUTx and VBAT) is 1.6V. So that's probably why the red LEDs were turning on but none of the others; the red LEDs have a lower forward voltage.

    How do I fix this issue? I've used the LP5024 on a previous design and we never saw this issue.

    Update: I cut all but one red LED signals, the red LED still showed the steady leakage. But when I cut the last red LED signal, the leakage current is now illuminating the green LEDs. 

    This issue is now on three of the eight boards we have.

    Thanks,
    Derek

  • 0 in reply to Derek
    TI__Genius 12915 points

    Hi Derek,

    First of all I think we should identify if leakage issue caused by IC or peripheral circuit. Could you help de-mount the LP5036 and power up the board to see if the leakage still exist?

  • 0 in reply to Hardy Wu
    Mastermind 9792 points

    Hello, the only thing this board has on it is the LP5036 and the LEDs. I removed the LP5036 and the problem totally went away. So then the issue is inside the LP5036. Also, I did not see any debris under the chip, it looks very clean.

  • 0 in reply to Derek
    TI__Genius 12915 points

    Hi Derek,

    It is not a normal behavior that LP5036 should have. Since some boards are good based on your description, I suspect that IC was damaged in unknown reason. To confirm it, could you help to do a A-B-A swap test (Mount abnormal IC to good board to see if leakage issue follow the IC, mount IC from good board to abnormal board to see if board have problem, mount abnormal IC back to abnormal board again to exclude solidering issue). If the issue follow the abnormal IC, I suggest you can contact local FAE for further failure analysis work.

  • 0 in reply to Hardy Wu
    Mastermind 9792 points

    Hello, we've been able to isolate this issue to the IC. Please PM me with contact info for our local FAE so we can get FA started immediately. This is an infection control product that's in high demand right now, so we want to get it into hospitals quickly.

    Thanks,

    Derek

  • 0 in reply to Derek
    TI__Genius 12915 points

    Hi Derek,

    Sorry that I do not know it. I think you can contact the sales or someone where you buy the ICs. Maybe you could find your local TI office information in below.
    http://www.ti.com/about-ti/contact-us.html#worldwide-locations