MAX17055 suitable for Lithium Carbon Monofluoride batteries?

Question : Is the MAX17055 Fuel Gauge IC suitable for Lithium Carbon Monofluoride batteries? Answer : Yes, but since this type of battery operate as primary cells there are caveats and certain steps needed to follow for the application to work as intended. Refer to article which also applies to MAX17055: How to Use The MAX17201/MAX17211 and MAX17205/MAX17215 to Fuel-Gauge Primary Cell Batteries | Analog Devices

What register on the MAX17055 shows the SOC based on just the voltage of the battery?

The VFSOC (FFh) register allows the user to find the battery SOC solely based off of the voltage of the battery instead of a combination of voltage lookup and coulomb counting. In addition, the VFOCV (FBh) register holds the value of the open-circuit voltage as measured by the fuel gauge.

What is the difference between BST, BI, BR bits setting in MAX17055?

In MAX17055, AIN pin is used to determine the BST, Bi and BR bits. If the AIN is detected, then BST = 0. If not, BST = 1. If BST changes from 1 to 0, then Bi = 1. If BST changes from 0 to 1, then BR = 1.

How do I convert the HEX values of IChgTerm and Vempty registers into decimal from a ModelGauge M5 fuel gauge?

The case of the register IChgTerm is much simpler to calculate. In order to achieve a value of 250mA (example in datasheet), we take the example hex value in the MAX17055 datasheet of 0x0640 and convert it to decimal, which is a value of 1600. We then multiply this value of 1600 by (01.5625 µV/RSENSE), which can be found in Table 1 of the datasheet in the "Current" row. RSENSE in this example is a10mΩ resistor. The register type can be found in the datasheet under the "IChgTerm" section. The product of 1600 and (01.5625 µV/RSENSE) gives you 250mA, which is the desired value. For the Vempty the desired VR value is 3.3V while the desired VE value is 3.88V for a hex value of 0xA561. On page 12 in Table 2, it can be seen that VR is the most significant 9 bits while VE is the least significant 7 bits. To calculate each of these, you convert the hex value to binary, take the first 9 bits for VR and last 7 for VE, and convert those values to decimal. VR will come out to be 330 and VE will come out to be 97. In the datasheet on page 13 under the VR section, a 10mV resolution is mentioned, meaning you must multiply 330 by 10 mV, giving you the desired 3.3V value. The same goes for VE except the resolution is 40 mV, meaning we multiply 40 mV by 97 to get the desired 3.88V value.

When MAX17055 is powered up from a dead battery by USB charging, the DevName is read but return value is different from value in datasheet. Why?

If MAX17055 lost power by VBATT < 2.3V, it needs VBATT > 3V to start operation. If MAX17055 is read or writen before the dead battery recovers to a high enough voltage, the operation is not reliable. The invaild DevName value means nothing, and customer should wait for the vaild DevName before other operation to MAX17055.

How can you achieve the lowest possible power consumption in the MAX17055?

There are two lower power states available in the MAX17055, hibernate mode and shutdown mode. In hibernate mode the IC consumes around 7uA of current and runs all of the normal functions of the fuel gauge but at a slower measurement update rate of 5.625 seconds while still remaining fully functional. In shutdown mode the IC consumes around 1uA of current and the internal LDO regulator is disabled, all activity stops, and A/D register and fuel-gauge output values are lost. More information on this can be found in the Modes of Operation section of the MAX17055 User's Guide.

Do you have the possibility of fuel gauging a LiNiMnCo battery?

There is an EZ model for Ni based batteries, but you will need to do some evaluation to see how well it works for you. If you are not satisfied with the performance, we can always do a custom model. For evaluation, you need to setup the EZ model and charge and discharge the battery with your application, and determine if the SOC readings are acceptable. For the custom model, you will need to ship the batteries to us for testing, and we will test them for ~2 weeks and extract the battery characteristics into a model file. Please keep in mind there may be an NRE for low volume applications.

Accessing the Timer and TimerH registers as one 32-bit register at MAX17055

In MAX17055, Timer register resolution is 175.8ms, that is when it reads 0xFFFF , 3.2Hrs time is elapsed. Whenever Timer register reaches 0xFFFF, TimerH register will increment by 1. Effectively TimerH resolution becomes 3.2hrs. So the range of both the registers together becomes 23.94yrs. At any given point of time if both registers are read then the time elapsed is calculated as, Time = (TimerH(decimal) * 3.2hrs) + (Timer(decimal) * 175.8ms).

There are two grounds on the MAX17055. How do I connect them?

There are two grounds in the application circuit of the MAX17055. One is the ground (CSP pin) of the MAX17055 IC, which should be connected to the negative end of the battery. The exposed pad of the IC (EP) and one end of the current sensing resistor are also connected to CSP. In addition, the system ground is connected to the load GND and the other end of the current sensing resistor, which is connected to CSN. Please see figure below from functional diagram in the datasheet:

MAX17048 datasheet states the ModelGauge algorithm "eliminates learning". Does it mean the the SoC of the battery can be read when the battery is inserted for the first time?

MAX17048 is a fuel gauge based on the battery model loaded to the device. The battery capacity can be accurately predicted after the battery model established by Maxim for the user is loaded to the device. Learning is not required once the model is loaded.

Does Maxim have a fuel gauge chip suitable for Panasonic NCR18650B?

MAX17055 is equipped with Panasonic NCR model, yet the precision of this model is not as high as the common lithium-ion battery. It you need more precise measurement, the battery needs to be characterized. The following is a snippet of the MAX17055 datasheet. Other ModelGauge m5 fuel gauge datasheets (MAX17201/11, MAX17205/15, MAX17260 - MAX17263) also recommend custom model for NCR cells for best performance.

How is Maxim's current offerings of fuel gauge different from Dallas's fuel gauge?

Maxim's new generation of fuel gauge is based on the technology of Dallas's fuel gauge with significant improvements in the algorithm and measurement circuit. The new battery fuel gauge products are more compact with higher precision, lower current consumption, and lower cost. For new designs, please refer to the following recommendations when selecting a replacement for Dallas's fuel gauge: 1. DS2780 > MAX17211 2. DS2781 > MAX17215 3. DS2782 > MAX17201 4. DS2740 > MAX17211 5. DS2745 > MAX17055 6. DS2746 > MAX17055 7. DS2756 > MAX17201 8. DS2438 > MAX17215

What battery chemistry is supported by EZ?

> LiCoO2 , most common > NCA/NCR > LiFePO4, LiMnO2, LiNiO2 etc

Why is characterization not needed with EZ?

> ModelGauge m5 algorithm is robust, learns, adapts to variations (load, temp, cell to cell, aging) > EZ model provides high accuracy for the most common Li+ batteries

Why is host side fuel gauge more cost effective?

> Host side fuel gauge is cheaper than pack side fuel gauge because it does not have NV memory > Host software writes the battery model to host side fuel gauge every time at IC power up

Difference between ModelGauge and ModelGauge m5 products?

please see below features for ModelGauge and ModelGauge m5: • ModelGauge > ModelGauge products provides good accuracy and smallest solution size > Most cost effective > Requires characterization • ModelGauge m5 > ModelGauge m5 products provides best accuracy and typically requires a current sense resistor > Eliminates characterization with EZ

Can I just implement some code in the microcontroller to do fuel gauging?

> This is a lot of effort and the accuracy will be poor > This approach drains battery quickly because uC can’t go to sleep mode

Why do I need a fuel gauge?

> If you have a rechargeable Li-Ion battery, you need one > Accurate fuel gauging is essential to the user experience > Unexpected shutdowns and short battery life are among the most common user complaints

What are the LSB units for the power (0xB1) and average power (0xB2) registers?

The power (0xB1) and average power (0xB2) registers are in 2’s compliment format with an LSB of 8μV 2 /Rsense. For example, a 10mΩ sense resistor will result in an LSB of 0.8mW (i.e. LSB = 8μV 2 /10mΩ = 0.8mW).

Can I use the MAX17055 like the MAX17201 with primary cells such as LiSOCL2 as described in App Note 6416?

The MAX17055 can do LiSOCL2 in the same manner as the MAX17201, though since it does not have non volatile memory all the parameters need to be reloaded when the power is removed.