For the MAX17201/05/11/15 Fuel Gauges, what should I do with the THERM, AIN1 and AIN2 pins if I do not implement temperature monitoring?

The easiest option is to leave all three pins unconnected. If you'd prefer to not leave them open, THRM, AIN1 and AIN2 can be tied to REG3 safely.

Can the MAX17205 be used with more than 15 cells in series?

The NCELLS bits in PackCfg register can only be programmed for a maximum of 15 cells in series; however, the MAX17205 can still monitor 16 or greater cells in series if the master ignores the NCELLS bits in PackCfg register.

How to power the MAX17205 with the battery pack of more than 4 cells in series?

When the battery pack is more than 4 cell in series, we can use below circuit to provide power supply for MAX17205, it includes 18V Zener, 500kohm resistor, a MOSFET and 1uF capacitor . The 18V Zener will clamp the gate voltage of the MOSFET within 18V. The MOSFET is on and charge the 1uF capacitor as Vgs>Vgs(th) and Vds>Vgs-Vgs(th). When the capacitor voltage reaches about 16V, the MOSFET turns off as Vgs<Vgs(th). The MOSFET will turn on and off to keep the capacitor at about 16V to power the MAX17205.

How to load a battery model without triggering an NV write cycle?

To load a battery model without triggering an NV write cycle, please follow steps below: 1. Load the fuel gauge model to the ModelGauge m5 registers (180h to 1DFh) 2. Reset IC fuel guage operation by writing 0001h to the Config2 register (0BBh) 3. Wait tPOR for fuel gauge to reset.

In MAX17201/5 GUI how to change the cell capacity?

In the configuration wizard, enter the actual capacity (Cell size) and click next and go to Step17. In step 17, Select the second option: "Write Configuration RAM and restart fuel gauge so changes take effect" Then Click "Update IC". Then the design Cap will be updated.

What is the MAX17205 I2C address?

The two I2C slave addresses for the MAX17205 are 0x6C and 0x16 as shown in Table 27 of the datasheet. Each address is used to access a separate portion of the internal memory.

How to achieve a proper boot sequence for the MAX17205?

When multiple cells are introduced one by one as mentioned in page 29 figure 3 in the datasheet, during insertion of the first cell, the micro-controller IC boots as voltage is induced across the pin and current flows. Some times the second cell or multi cell insertion could cause bad booting and there might be some high currents drawn. This can be oversome by introducing the balancing resistance of around 100 ohms across each cell and making Cellx pin open. The packcfg.chEN register has to be set accordingly based on the application for these kind of multi-cell configuration.

How to achieve cell balancing for the MAX17205 in a low power application?

In the MAX17205 the status of nPackCfg Register has to be configured as mentioned in Page 59 in the data sheet. nPackCfg Register has to be set to suit the configuration selected for the number of cells and selecting the threshold voltage for balcfg register accordingly. It has to match the hardware selected for the purpose as each hardware has different settings. Typical circuits can be found on page 27 in the data sheet.

After selecting a default Murata thermistor in the MAX17201/205/211/215 ModelGauge GUI, the Configuration wizard clears the nTGain and nTOff registers. Is this a bug?

This is not a bug because the Murata thermistor chooses the default values of the TGAIN and TOFF. When the default values are chosen, the nTGAIN and nTOFF registers are cleared to make the NV memory space open for user memory, and the default values are loaded from ROM instead. If you choose the third option in the list, or pick a non default value, then the nTGAIN and nTOFF will be set with their custom values, and the enTGO bit will be set.

How to use memory locks in MAX1720x design?

ModelGauge m5 RAM Registers and all nonvolatile memory locations can be permanently locked to prevent accidental data loss in the application. Locking a memory block only prevents future writes to the locations. Reading locked locations is still allowed. You can lock the RAM separately and leave NV ram unlocked, or lock individual columns on NV memory, and leave some columns or leave RAM unlocked. Each LOCK may be set separately or together. If you want to lock RAM only, this is controlled by Lock2. This is set by writing the register to 0x6A02. NV RAM only is set by locking registers 0x18_ to 0x1D_, which is achieved by setting lock1, 3,4,5. TO do this, send the command 0x6A1D. If you only wanted to lock the model table and SN, and Device Name, (columns 0x18, 0x19, and 0x1D), you would need to set locks 1 and 5. This is done by command 0x6A11. The “Sets no locks” means it won’t lock any unlocked blocks. For example, if you have lock 1 set, and you want to change the memory for the OCV table, writing 0x6A00 won’t unlock the Lock1 register block, but it also won’t lock any other register blocks. So if you wanted to lock any register block, you bit OR it with the 0x6A00 command to set that lock only.

Could MAX17205 be supported for monitoring and balancing a 4S pack?

MAX17205 could monitor and balance 2S or 3S pack. Can't support balance 4S pack, but MAX17205 could monitor 4S or a multiple-series cell pack

When using the MAX17205, how do we determine if the battery is charging or discharging?

You can check the magnitude of the current on the current-sense resistor (i.e., register 6C:0A, or 00A) to determine if the battery is charging or discharging: When the value is larger than a certain value (the smallest charging current, for example, 10mA), the battery is charging. When it is smaller than a certain value (smallest discharging current, for example, -10mA), it is discharging.

Choosing the right part for measuring 8-cell lithium iron phosphate (LiFePO4) battery

An 8-cell lithium iron phosphate battery power can be measured by the MAX17205. However, the characteristics of different LiFePO4 batteries may vary by a lot. Before using the MAX17205, models need to be built to reflect the corresponding battery characteristics and application conditions for accurate measurements.

How do l convert the current register value to actual current value for MAX17201, MAX17211, MAX17205, MAX17215?

Current register format is in 2's complement. The LSB size is 1.5625uV/RSENSE, where RSENSE is the sense resistor. For example, for MAX17201evkit, the default sense resistor is 0.01ohm. Thus the LSB size would be 1.5625uV/(10mohm) = 0.15625mA The table below is a capture from the evkit GUI as an example. To convert from 0xF163 to the corresponding current, the calculation is as follow: Since the most significant bit is high, this is a negative current. To convert from the binary value to decimal, 0xFFFF-0xF163+1=0x0E9D=3741 in magnitude. current = -3741*0.15625mA=-584.53125mA, which matches the value posted in the GUI above.

The voltage, current, and temperature values read from MAX17201, MAX17205, MAX17211, MAX17215 are correct, but the RepSOC is always 1.0%. Why is that?

The tips below may be helpful: 1. When configuring the registers, the battery cannot be charging or discharging as OCV estimation takes place after the setup. If there is any current during that period, the OCV may be incorrect, introducing error to RepSOC. 2. For multi-cell battery, the battery capacity is related to the number of cells connected in parallel, not the batteries connected in series. For example, for 2600mAh cell connected in 3S1P, the capacity of the battery pack is still 2600mAh. It is not 2600*3 =7800mAh.

Should the I2C address of MAX17201, MAX17205 be 0001011x or 0010110x?

The MAX17205 has two I2C addresses: One is 0x16(0001 011x) , and the other is 0x6C(0110 110x) . Different slaves addresses are used according to different internal addresses being accessed, as shown in table 27 of the datasheet (Rev 2; 8/16).

The MAX17201, MAX17211, MAX17205, MAX17215 nPackCfg Register (1B5h) is related to battery pack configuration. Should this register have the same content as PackCfg (0BDh) register?

PackCfg (0BDh) is the address of a non-volatile register. If MAX17205 is placed with the battery pack (i.e pack side), 0BDh does not need to be written. As the battery will constantly supply power to the MAX17205, the value in the non-volatile register (1B5h) will not get lost. However, if the MAX17205 is placed on the host side, the correct battery configuration needs to be written to 0BDh. This is because the data that is stored in 0BDh will be written into 1B5h after changing the battery and MAX17205 is powered up again. It must be noted that there is a limit to the number of times that the non-volatile register can be written; It can be written up to seven times (page 84 of the datasheet (Rev 2; 8/16))

Does MAX17205 support Nickel-cadmium (NiCd) batteries or Nickel-metal-hydride (NiMH) batteries?

MAX17205 is designed for lithium batteries and does not support fuel gauging of Nickel-cadmium batteries or Nickel-metal-hydride batteries. Please consider using Maxim's earlier product, DS2438, for fuel-gauging nickel-cadmium batteries or nickel-metal hydride batteries.

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MAX17205G+T: FAQ

Q: How to load a battery model without triggering an NV write cycle?

To load a battery model without triggering an NV write cycle, please follow steps below: 1. Load the fuel gauge model to the ModelGauge m5 registers (180h to 1DFh) 2. Reset IC fuel guage operation by writing 0001h to the Config2 register (0BBh) 3. Wait tPOR for fuel gauge to reset.

Q: In MAX17201/5 GUI how to change the cell capacity?

In the configuration wizard, enter the actual capacity (Cell size) and click next and go to Step17. In step 17, Select the second option: "Write Configuration RAM and restart fuel gauge so changes take effect" Then Click "Update IC". Then the design Cap will be updated.

Q: What is the MAX17205 I2C address?

The two I2C slave addresses for the MAX17205 are 0x6C and 0x16 as shown in Table 27 of the datasheet. Each address is used to access a separate portion of the internal memory.

Q: How to achieve a proper boot sequence for the MAX17205?

When multiple cells are introduced one by one as mentioned in page 29 figure 3 in the datasheet, during insertion of the first cell, the micro-controller IC boots as voltage is induced across the pin and current flows. Some times the second cell or multi cell insertion could cause bad booting and there might be some high currents drawn. This can be oversome by introducing the balancing resistance of around 100 ohms across each cell and making Cellx pin open. The packcfg.chEN register has to be set accordingly based on the application for these kind of multi-cell configuration.

Q: How to achieve cell balancing for the MAX17205 in a low power application?

In the MAX17205 the status of nPackCfg Register has to be configured as mentioned in Page 59 in the data sheet. nPackCfg Register has to be set to suit the configuration selected for the number of cells and selecting the threshold voltage for balcfg register accordingly. It has to match the hardware selected for the purpose as each hardware has different settings. Typical circuits can be found on page 27 in the data sheet.

Q: After selecting a default Murata thermistor in the MAX17201/205/211/215 ModelGauge GUI, the Configuration wizard clears the nTGain and nTOff registers. Is this a bug?

This is not a bug because the Murata thermistor chooses the default values of the TGAIN and TOFF. When the default values are chosen, the nTGAIN and nTOFF registers are cleared to make the NV memory space open for user memory, and the default values are loaded from ROM instead. If you choose the third option in the list, or pick a non default value, then the nTGAIN and nTOFF will be set with their custom values, and the enTGO bit will be set.

Q: How to use memory locks in MAX1720x design?

ModelGauge m5 RAM Registers and all nonvolatile memory locations can be permanently locked to prevent accidental data loss in the application. Locking a memory block only prevents future writes to the locations. Reading locked locations is still allowed. You can lock the RAM separately and leave NV ram unlocked, or lock individual columns on NV memory, and leave some columns or leave RAM unlocked. Each LOCK may be set separately or together. If you want to lock RAM only, this is controlled by Lock2. This is set by writing the register to 0x6A02. NV RAM only is set by locking registers 0x18_ to 0x1D_, which is achieved by setting lock1, 3,4,5. TO do this, send the command 0x6A1D. If you only wanted to lock the model table and SN, and Device Name, (columns 0x18, 0x19, and 0x1D), you would need to set locks 1 and 5. This is done by command 0x6A11. The “Sets no locks” means it won’t lock any unlocked blocks. For example, if you have lock 1 set, and you want to change the memory for the OCV table, writing 0x6A00 won’t unlock the Lock1 register block, but it also won’t lock any other register blocks. So if you wanted to lock any register block, you bit OR it with the 0x6A00 command to set that lock only.