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I want to power my nodemcu module with 3.3 V.

Does powering it with 3.3 V also power USB-UART module?

If so I do not want this as it eats the battery.

enter image description here

Bence Kaulics
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a-c-sreedhar-reddy
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1 Answers1

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Yes, the schematic of the v1.0 NodeMCU shows that the 3.3 V bus is directly connected to the CP2102 chip.

enter image description here

You have two possibilities:

  1. Cut the 3.3 V trace on the PCB before the CP2102 chip. Not recommended as you will disable your programming interface and would be hard to restore it.
  2. The reset pin (RST) pin of the CP2102 is floating, you can try to pull it down to GND and keep the chip in reset, to see if that makes it any better.
Bence Kaulics
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  • But in deepsleep mode when the current is measured with a multimeter it is 0.000 – a-c-sreedhar-reddy Jul 24 '18 at 12:04
  • Are you sure that you are measuring it correctly? 0.000 seems strange also it means nothing without units. – Bence Kaulics Jul 24 '18 at 12:32
  • Sorry it is showing 0.00 – a-c-sreedhar-reddy Jul 24 '18 at 13:18
  • And is it kA, A, or uA it matters a lot? 0.00 without SI unit is just a number and nothing else. – Bence Kaulics Jul 24 '18 at 13:21
  • 0.00 amperes using multimeter – a-c-sreedhar-reddy Jul 24 '18 at 13:22
  • @ACSreedharReddy change your multimeter's measurement range to micro amps and repeat the measurement. Also I think you got the answers regarding the USB-UART module. For further decreasing the consumption you already have an other open question. – Bence Kaulics Jul 25 '18 at 11:38
  • Note that cutting the power to an IC is likely a data sheet violation unless explicitly allowed, ie, if the input voltage range is not relative to Vdd. If any of the signals to it are high, you may end up re-powering it through the protection diodes. – Chris Stratton Jul 25 '18 at 16:39
  • @ChrisStratton True, true. By the way the input voltage range is not relative to VDD. Also there is a part in the datasheet "In addition, if VDD or REGIN may be unpowered while VBUS is 5 V, a resistor divider (...) shown in Note 1 of Figure 8 is required to meet the absolute maximum voltage on VBUS specification in Table 2.". Based on this I think it is fine if VDD and REGIN are unpowered, nevertheless it was a hasty statement from me and if someone choose to give up on the UART-USB module it is better to entirely remove it from the board. – Bence Kaulics Jul 25 '18 at 20:04
  • Yes, looks like it's a 3v3 part with 5v tolerant I/O. That input structure can often deal with an I/O voltage even in the complete absence of supply. So probably OK in this case. – Chris Stratton Jul 25 '18 at 20:46