Comments: LTC4150 Coulomb Counter Hookup Guide

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  • I want to replace the sense resistor to give me more sensitivity at a maximum of 250ma, or even at a max of 100ma (my expected max current draw is 25ma@3v). Yesterday, I ordered two more Coulomb Counters so I can mod them, and I wanted to order the resistors. What is not mentioned in the suggestion about replacing the resistor is its form factor. 0603? I can’t find the one I have to measure the resistor, but I know which pile it is in, and know that it will show up eventually as I sort that pile out, but I need an answer today so I can place the order. The possible replacements will be 100mΩ (500ma max), 200mΩ (250ma max), or 500mΩ (100ma max).

    I also have a need to measure the actual coulombs consumed by my circuit, and it makes no sense to run the coulomb counter itself from Vin. This would make sense only if the processor is monitoring its own supply (a future design should make this an option) Another mod I plan to make is to cut the IN+/VDD trace and resolder it to be Vio/Vdd. I am working with a 3.0V/240mAh primary battery (CR2032) and only care about how much power my circuit, and my circuit alone, consumes. There is no charger involved, so I can ignore POL, but I will include it in my software in case I ever need to measure a LiPo. My “host computer” that powers it is a Cortek M0 (3.3V) core. The instructions for jumpers j2 and j3 do not make it clear what should be soldered when a 5V system is monitoring a 3.3V system, or (if it is possible) a 3.3V system is monitoring a 5V system. The options should be specific about whether the host or target voltages matter, and allow for self-monitoring of battery and using one system to monitor another.

  • sorry but there is one thing i dont understand, does the out pins (out + and out - ) have to be connected ?

  • Couple of things that really should be mentioned in the guide…and one on the device spec sheet really.

    The Shutdown mode isn’t actually that useful as it seems to forget part counted coulombs, the spec sheet hardly mentions this but it’s an issue which will slowly add errors to your count if you shutdown the counter frequently. For our particular application we draw less than one coulomb between sleep cycles so it meant we never saw any counts.

    On the sparkfun board there is no pull up resistor for the CLR port. So if you intend to use this device in polling mode then make sure you pull it up to VIO yourself or have your controller pull the pin high to enable the counter.

    EDIT

    Actually it’s worse than that, VIO will draw circa 1mA at 3.3v regardless of shutdown state, so if you intend to use this in a circuit that needs a low power sleep state with the battery still in circuit then do not wire VIO to your 3.3V supply, wire it to something you can set low when in the sleep state and ignore the shutdown pin, it serves no useful function as far as I can tell.

  • I was the original design engineer for Linear Technology’s LTC4150 Coulomb Counter, in 1999-2002.

    POL should NOT be wired directly to a power supply or grounded. It’s an open-drain output that needs a pullup resistor to your supply / battery at 9V or less. Since it’s open-drain, floating it may not be a good idea either. Floating shouldn’t give you a problem with the ESD diodes, but could recult in unpredictable operation. You’re much better off connecting it via a pullup resistor. You need it connected anyway to tell the difference between battery charge and discharge, for an accurate coulomb count.

    The silicon process the LTC4150 is designed in has a breakdown limit between 9.5 and 11 V, so anything above 9V is a no-no. The absolute maximum ratings limit you to -0.3V to 9V at any pin without damage.

    • Belated thanks for chiming in; it’s always good to hear from the original engineers on a part!

      We do connect the POL signal to a pull-up resistor on the board as you can see on the schematic. We’ve also endeavored to inform users (through this guide and silk on the PCB) that the maximum battery voltage is 8.5V. Please let us know if you noticed that we’re violating either of these criteria; we certainly shouldn’t be.

  • Hi, I just received this unit and have connected as per the instructions, the load is between 50 and 120 ma @ 5 volts, I have now been monitoring the INT pin for 30 minutes and it has not gone low once, I think something is wrong.

    The source is a 3V3 Lipo battery, here’s the connections:

    VIO > 5v Power Supply GND > 5v Power Supply Ground POL > 5v Power Supply Ground INT > SCOPE ( & Ground)

    IN = 3v3 LIPO OUT = Load 50 - 100ma

    How can I verify that the device is actually working ??

    • From your description, I think you’re using POL incorrectly. POL is an output (it tells you the POLarity of the current draw), so it should be connected to an input on your microcontroller (or left disconnected if you don’t care about the polarity). Connecting it to GND may be disabling the INT output. Try leaving POL disconnected and see if you get pulses from INT. If you don’t, contact our tech support department, they’ll be delighted (really!) to help you troubleshoot further.

  • Hello, I purchased and tested the device. It worked all fine. I want some suggestions. I want to test the coulomb counter with 12V 100Ah lead acid battery from which current can be drawn more than 5 A. How can I do this? In this (LTC 4150) the max current capacity is 1A. Thanks in advance.

    • Sorry we didn’t see this earlier. Unfortunately, the LTC4150 is limited to 8.5V maximum, so it won’t work with a 12V supply. We’re looking at other parts that do support higher voltages, so we may have an updated board in the future.

  • Hi, is there anyway to connect a microusb from a power bank to the coulomb counter?

    • Sure! The easiest way would probably be to take a USB cable, cut it in half, and connect the input half to the input of the coulomb counter, and the output half to the output of the coulomb counter. There should be red and black wires in the USB cable for power and ground, but those colors aren’t guaranteed, so use a multimeter and the USB pinout to verify you have the right connections. Good luck!

  • Hi, I noticed the schema image is beautifull, especially the connection lines. What kind of software do you use to draw such connections?

    • All of our hookup pictures are done using a program called Fritzing. We like it because its free, open source and makes pretty lines.

      • I actually cheated a bit ;) and used Inkscape along with the product photos our amazing photographer Juan takes for us. For the connection lines, I drew a line where the wire was supposed to go, made it fairly thick, then converted the line (“path”) to a shape (“object”). Once you do that, you can separately control the outline and the fill colors. Thanks for the compliment!


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