BQ27541 Datasheet, PDF(24/38 Page) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

◁

bq27541

SLUS861 â DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com

Qmax

Qmax contains the maximum chemical capacity of the active cell profiles, and is determined by comparing states

of charge before and after applying the load with the amount of charge passed. They also correspond to capacity

at low rate of discharge, such as C/20 rate. For high accuracy, this value is periodically updated by the bq27541

during operation. Based on the battery cell capacity information, the initial value of chemical capacity should be

entered in Qmax field. The Impedance Trackâ¢ algorithm will update this value and maintain it in the Pack

profile.

Update Status

Bit 0 (0x01) of the Update Status register indicates that the bq27541 has learned new Qmax parameters and is

accurate. The remaining bits are reserved. Bits 0 is a status bit set by the bq27541. Bit 0 should never be

modified except when creating a golden image file as explained in the application note Preparing Optimized

Default Flash Constants for specific Battery Types (SLUA334.pdf). Bit 0 is updated as needed by the bq27541.

Avg I Last Run

The bq27500 logs the current averaged from the beginning to the end of each discharge cycle. It stores this

average current from the previous discharge cycle in this register. This register should never need to be

modified. It is only updated by the bq27541 when required.

Avg P Last Run

The bq27541 logs the power averaged from the beginning to the end of each discharge cycle. It stores this

average power from the previous discharge cycle in this register. To get a correct average power reading the

bq27541 continuously multiplies instantaneous current times Voltage( ) to get power. It then logs this data to

derive the average power. This register should never need to be modified. It is only updated by the bq27541

when required.

Delta Voltage

The bq27541 stores the maximum difference of Voltage( ) during short load spikes and normal load, so the

Impedance Trackâ¢ algorithm can calculate remaining capacity for pulsed loads. It is not recommended to

change this value.

Default Ra and Ra Tables

These tables contain encoded data and, with the exception of the Default Ra Tables, are automatically updated

during device operation. No user changes should be made except for reading/writing the values from a

prelearned pack (part of the process for creating golden image files).

DETAILED PIN DESCRIPTIONS

System Shutdown Enable (SE Pin)

If the CONTROL_STATUS[SHUTDOWN] has been set, bq27541 will immediately pull the SE pin low at POR.

The fuel gauge can be made to power-off through an external circuit when it releases the SE pin to high

impedance. With an external circuit, this feature is useful to shutdown the fuel gauge in a deeply discharged

battery to protect the battery. The SE pin is released to open drain state when the gauge enters HIBERNATE

mode with the CONTROL_STATUS[HIBERNATE] and [SHUTDOWN] bits set.

The Pack Configuration Register

Some bq27541 pins are configured via the Pack Configuration data flash register, as indicated in Table 10. This

is located at subclass = 64, offset = 0.

Submit Documentation Feedback

Product Folder Link(s): bq27541

▷