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I have designed a wearable device and added a MAX30102 to it (MAX30102 home page, datasheet). The datasheet says the maximum current drawn by the IC (excluding the LEDs) should be 1200uA or 1.2mA.

The switching regulator can provide up to 200mA of 1.8V, and I have tested that. But as soon as I solder the MAX30102 back on it, the 1.8V drops to 0.8V and current increases from 5mA (of the whole PCB) to 95mA. So that's a 90mA increase caused by the MAX30102. The only thing using 1.8V rail is this IC.

I have attached the schematic of my PCB, as well as the typical application circuit in the ICs datasheet. and I cannot figure out why this is happening.

MAX30102 schematic MAX30102 typical application PCB render Actual PCB PCB text

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    \$\begingroup\$ Have you traced where the current goes? Is the MCU with 3.3V IO voltages or 1.8V IO voltages? \$\endgroup\$
    – Justme
    Feb 22, 2021 at 12:09
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    \$\begingroup\$ Usman Mehmood - Hi, (a) Can you please edit the question and add a close-up photo of the PCB showing the MAX30102 and surrounding components, in case readers notice anything? (b) How are you soldering the MAX30102 to the PCB? Hand soldering, or hot air, or heated oven, or something else? (c) Is this the first time you have soldered a MAX30102 onto your PCB, or have you done that before? If you have done it before, was your soldering process successful? (d) When you got the excessive current on the 1.8 V rail, did you have any connections or pull-up resistors on SDA, SCL, -INT signals? Thanks. \$\endgroup\$
    – SamGibson ♦
    Feb 22, 2021 at 23:43
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    \$\begingroup\$ Hi @SamGibson The MAX30102 was soldered by a PCBA factory using a pick and place machine and whatever heating equipment they used. I had 5 units, all with the same problem. I re-soldered one unit with hot air, but it made no difference. The SCL, SDA, and INT pins are being pulled up to 3.3V by 4.7k resistors. \$\endgroup\$
    – Usman Mehmood
    Feb 24, 2021 at 6:26
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    \$\begingroup\$ Where on the board is the 1V8 line connected to the supply? On these pictures I can see no via connecting the trace with anything other than C2 and C6 (by the way, why would you place the 100n C2 further away from the pins than the 4.7µ C6? That does not make sense and renders C2 quite useless). \$\endgroup\$
    – jusaca
    Feb 24, 2021 at 8:58
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    \$\begingroup\$ @jusaca The 1V8 line is the one you see exactly below the marking "IC1". You are right, I should have placed the 100nF cap closer to the pin than the 4.7uF cap. Thank you. :) \$\endgroup\$
    – Usman Mehmood
    Feb 24, 2021 at 9:45

1 Answer 1

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The 1.8 Vdd input on the chip only powers the ADC's and some digital logic. Unless there is internal damage, the pin should not draw anything like 95 mA.

Possibility #1: in this land grid package with 0.8 mm pitch between pads, the 1.8 Vdd pin (11) and the GND pin (12) are adjacent. Are you sure you don't have a solder bridge between those pins under the IC?

Possibility #2: could you have the IC flipped 180 degrees? That would feed the 1.8 Vdd into the LED driver ground pin.

Possibility #3: the chip is damaged. Bummer, but double check all your connections before you put in a new one. Good luck!

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    \$\begingroup\$ Hi @mark The sensor was indeed flipped by 180 degree. I de-soldered, corrected and soldered it back. Now the power is all good. Thanks for the suggestion. :) \$\endgroup\$
    – Usman Mehmood
    Feb 24, 2021 at 9:41
  • \$\begingroup\$ Thank you for the feedback! The IC lacks the standard Pin 1 marking, so it’s easy for the assembler to make this error. If there’s room, it may help to have a little drawing of the IC appearance on the silkscreen. \$\endgroup\$
    – Mark Leavitt
    Feb 24, 2021 at 15:57
  • \$\begingroup\$ You are very right. I will put a little drawing next to the IC on my future PCBs. \$\endgroup\$
    – Usman Mehmood
    Feb 26, 2021 at 5:42
  • \$\begingroup\$ Hello @UsmanMehmood thank you for sharing your question and analysis, I am working with a similar application with MAX30102, could I use your schematic? I have been analyzing many proposals from different makers, did you share your projetc in github? or is it a private project? thank you in advance! \$\endgroup\$
    – imt_blake
    Nov 6, 2022 at 4:55

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