Does the MAX17055 have a minimum supported battery capacity?

MAX17055 has no minimum battery capacity limits because unlike the MAX17262 the sense resistor can be changed to accommodate any value of battery capacity.

Does the MAX17055 provide overdischarge, or overcharge protection?

The MAX17055 does not have hardware comparators for fast protection on overdischarge, overcharge, or short circuit. These kind of events can damage the cells much faster than the MAX17055 can protect them. The MAX17055 ALRT being open drain active low means by default the the FETs are on, even if the MAX17055 is shutdown/dead/damaged. This is an unsafe condition. The MAX17055 has no special treatment for overcurrent events. If there is short circuit present on the output pins, MAX17055 will shut off the FETs after ~175ms. There should be dedicated ICs for primary safety protection for these events.

Can the MAX17055 switch the battery off using the alert pin driving an external FET?

The MAX17055 alert pin is an active low output. The drive range is from the supply (BATT+ ) to GND. This limits the high side FET to be a PFET. A PFET solution will require an additional inverter on the ALRT pin output to pull the gate low to allow the charge/discharge of the battery when no alert condition is present. This solution will make the system more prone to faults, hence the ALERT pin cannot be used to control the battery charging or used as master to control any slaves attached to it.

How do I check that I have the I2C connection setup properly on the MAX17055?

The MAX17055 supports the slave address 0x6C (or 0x36 for 7 MSbit address). Regardless of the fuel gauge configuration, if the I2C bus is functional, you will be able to read Vcell content. If you have the battery cell is connected, then you will be able to read Vcell content since device will make the analog reading and register will be populated with raw data. In term of troubleshooting I2C communication, we recommend to monitor the SDA and SCL on the scope to ensure they are transferring data as expected and ensure the none of these lines are held low for any reason, that will prevent host from reading values from the device.

Is the MAX17055 compatible with the CG-320A, Panasonic battery?

We can’t seem to locate the chemistry type of the this battery and it doesn’t look like Maxim has characterized it before. You can start with the default model and after a few cycles if it does not perform well then a customized battery characterization would be required.

MAX17055 enters and exits hibernate when the battery current is less than about C/100. What is C?

C rate is relative to the battery capacity. For example, C/100 on a 1000 mAh battery is 10 mA.

Battery Characterization at Low and High extended temperatures up to +70C

Maxim fuel gauge battery characterization for customer's batteries is done at 0 ֯ C, +20 ֯ C and +40 ֯ C. Regarding the characterization at 70 ֯ C, we characterize up to 60 ֯ C. The reason being that the cells do not change behavior at high temperature as they do at cold; the cell model changes are minimal, if any, from 60C to 70 ֯ C – assuming the cell is safe to operate. So no new model is needed. Test data on run-times at 60 ֯ C and 20 ֯ C is virtually the same. From a high-level perspective, it is disruptive to run characterization at temperatures other than 0, 20 and 40 ֯ C because the temp chamber cannot be used for anything else during that time. We can do a special case for customers if it is absolutely necessary. However, it looks like the battery characteristics change in a very minor way.

What is the smallest current a running MAX17055 fuel gauge is able to measure and use in algorithm calculations?

The smallest current that the MAX17055 is able to measure and update for use in the ModelGauge algorithm is based on the sense resistor selection. Anything lower than the measurement resolution will not be accurately accounted for in the current measurements used in the ModelGuage algorithm. Please see the Current Measurements section of the User's Guide for more information.

Do you have to backup any registers or parameters of the MAX17055 to external nonvolatile memory before going into shutdown mode?

No, you do not need to backup any registers before entering shutdown mode in the MAX17055. In shutdown mode, the internal LDO regulator is disabled, all activity stops, A/D register and fuel-gauge output values are lost but the MAX17055 still retains other important register values including battery parameters, configuration, and status. It is however recommended to save the learned parameters to nonvolatile memory periodically in case there is a sudden loss of power to the IC (not due to shutdown mode).

Why is the battery capacity measured by the MAX17055 less than 100% despite being fully charged?

The MAX17055 can be used to obtain accurate measurement of the battery capacity without characterizing the battery. Only a simple configuration of the MAX17055 is necessary (e.g battery capacity, charge termination current, and empty voltage). However, it should be noted that the difference between the configured battery capacity and the actual battery capacity cannot be too large because it may not be possible to measure the full battery capacity accurately. For example, if the actual battery capacity is 1000mAh, and if the capacity register in the MAX17055 is configured to be 2000mAh, the capacity may not converge to 1000mAh even after multiple charging and discharging cycles.

LSB size of capacity for MAX17055

LSB size capacity is "5.0Vh/Rsense" with 0.010 ohm in Table 6 of MAX17055 datasheet. So what would be the LSB capacity for 0.020 ohm sense resistor ? The capacity LSB is expressed in uVh/RSense regardless of the RSense. For example, if you have a 10mOhm sense resistor: 5uVh/0.01 ohms = 500uAh -> 0.5mAh. When your sense resistor changes, the RSense denominator changes, but the numerator LSB (uVh) remains the same. For example: 20mOhm, the equation becomes 5uVh/0.02ohms = 250uAh -> 0.25mAh. For current, the LSB is expressed in uV/Rsense, and dividing by ohms gives you a uA or mA LSB with scaling.

How often do ModelGauge m5 registers update?

Registers are automatically updated once per firmware cycle, which happen every 175.8ms in Active mode and every 5.625s in Hibernate mode by default. The Hibernate mode period can be modified through the HibCfg register. Registers can be written at any time and new settings will go into effect at the next firmware cycle (up to 175.8ms or 5.625s). For changes to the AtRate register, wait at elast two firmware cycles (351ms or 11.25s) before reading the AtTTE, AtAvSOC, or AtAvCap registers. Reading or writing registers does not affect the firmware cycle timing or cause the fuel gauge to exit Hibernate mode.

Use MAX17055 Fuelgauge to measure voltage accurate up to 1mV?

Question: How to get accurate voltage of the battery up to 1mV? Answer: Using VFOCV to measure the voltage is more accurate. The VFOCV can reach the real value of the voltage more quickly if set RCOMP0=0x0000. It needs about several minutes if the initial value of VFOCV is not quite far from the real value. If the VFOCV is too far from the real voltage, software reset the IC first.

For MAX17055, if we use the normal Li battery, which initial is best?

We would recommend they start with the EZ config model. This will accelerate their development cycle, since there is no need for characterization. If they find that the EZ config model observes an error in the reported capacity greater than 3% then the battery must be characterized. The EZ config model provides less than 3% error for most battery chemistry. For battery chemistries like NCR/LiPO they may need a battery characterization.

MAX17055 is used for 3 different projects and the battery pack is removable. If there is 20% aged battery and plug in to system, what’s the fastest way through charging/discharging so that ModelGauge m5 can know the battery is aged?

The fuel gauge capacity learning is still similar to ModelGauge m3 dq_Acc and dP_Acc learning. MAX17205 is a bit different because it initializes the dQ_Acc value to 25%, while MAX17055 initialize to 200%. However, since MAX17055 and MAX77818 are host side, they could change the initialization firmware to write these values to 25% of initial capacity. The learning will happen through monitoring coulomb counter accumulation and delta percentage accumulation. I have a table below that shows the accumulation for a 20% aged battery. After the first ~ 4 cycles, a 1000 mAh battery will be learned to 810 mAh, and afterwards the changes are very gradual. Actually, just the first full charge or discharge is enough to learn 160 mAh difference (80% of capacity loss). The 100% cycle here is 100% VFSOC change, not 100% charge + 100% discharge. To make sure the learning is managed best, there should b e a 45 minute rest near full and empty to allow FullCapNom to update. VFSOC is the calculated present state of charge of the battery according to the voltage fuel gauge.

How do I convert from the voltage, current, and capacity to the register values of MAX17055, and vice versa?

For calculations regarding voltage, current, and capacity of the MAX17055, please use the register resolutions in the table on page 16 of the datasheet. For example, for a 5000mAh battery: If we use a 10mohm sense resistor, the register value for capacity is 5000 mAh / (5uVh/ 10mOhm) = 10000 in decimals. In hexadecimal, it is 0x2710, that is, 0x2710 should be written into the DesignCap Register (18h).