The datasheet of TI bq40z50-R2 (Li-Ion Battery Pack Manager) tells that "The SMBus clock and data lines have internal pulldown".

Pin equivalent Diagram is in image below: Pin equivalent Diagram

Aren't usually the SMBus Data and Clock lines to be connected to pull-up resistors?

I'd like to connect this IC and a Battery Charger IC to same SMBus, but the latter requires pull-up resistors for the SMBus lines.

Would this work anyway?



1 Answer 1


The internal pull-downs in question are very weak, 1 MΩ. They are not meant to be "operational", and won't have any effect on normal I2C data transactions when the standard (10k-5k or 2k) pull-ups are attached to the I2C system bus. The reason for weak pull-downs is to provide well-defined bus state during power-on transients, when not all parts of the system are yet powered up.

The initial state with pull-downs is used by internal logic of the IC, per datasheet P.34:

When the gas gauge senses that both lines are low (such as during removal of the pack),the device performs auto-offset calibration and then goes into SLEEP mode to conserve power"

  • 1
    \$\begingroup\$ Just a tip: you can use HTML symbols in the posts. &Omega;, &mu;, &deg;, etc. For superscripts and subscripts use HTML <sup>...</sup> and <sub>...</sub>. They don't work in the comments. \$\endgroup\$
    – Transistor
    Mar 31, 2019 at 20:31
  • \$\begingroup\$ Ok, thanks for the explanation! \$\endgroup\$
    – haku15
    Mar 31, 2019 at 21:15
  • \$\begingroup\$ @Transistor, thanks, and don't delete your comment - I will use it as future guide:-) \$\endgroup\$ Mar 31, 2019 at 21:21

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