BQ27510-G2 Datasheet, PDF (21/38 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Direct Battery Connection

bq27510-G2
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SLUS948 – AUGUST 2010
Quit Current, Dsg Relax Time, Chg Relax Time, and Quit Relax Time
The Quit Current is used as part of the Impedance Track™ algorithm to determine when the bq27510-G2 enters
relaxation mode from a current flowing mode in either the charge direction or the discharge direction. The value
of Quit Current is set to a default value of 40 mA and should be above the standby current of the system.
Either of the following criteria must be met to enter relaxation mode:
1. | AverageCurrent( ) | < | Quit Current | for Dsg Relax Time
2. | AverageCurrent( ) | > | Quit Current | for Chg Relax Time
After about 30 minutes in relaxation mode, the bq27510-G2 attempts to take accurate OCV readings. An
additional requirement of dV/dt 4 mV/sec is required for the bq27510-G2 to perform Qmax updates. These
updates are used in the Impedance Track™ algorithms. It is critical that the battery voltage be relaxed during
OCV readings to and that the current is not be higher than C/20 when attempting to go into relaxation mode.
Quit Relax Time specifies the minimum time required for AverageCurrent( ) to remain above the QuitCurrent
threshold before exiting relaxation mode.
Qmax 0 and Qmax 1
Generically called Qmax, these dynamic variables contain the respective maximum chemical capacity of the
active cell profiles, and are determined by comparing states of charge before and after applying the load with the
amount of charge passed. They also correspond to capacity at very low rate of discharge, such as C/20 rate. For
high accuracy, this value is periodically updated by the bq27510-G2 during operation. Based on the battery cell
capacity information, the initial value of chemical capacity should be entered in the Qmax n field for each default
cell profile. The Impedance Track™ algorithm updates these values and maintains them in the associated actual
cell profiles.
Update Status 0, Update Status 1
Bit 0 (0x01) of the Update Status n registers indicates that the bq27510-G2 has learned new Qmax parameters
and is accurate. The remaining bits are reserved. Bits 0 is a status flag that can be set by the bq27510-G2
although a user can modify it. 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 bq27510-G2.
Avg I Last Run
The bq27510-G2 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 bq27510-G2 when required.
Avg P Last Run
The bq27510-G2 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
bq27510-G2 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 bq27510-G2
when required.
Delta Voltage
The bq27510-G2 stores the maximum difference of Voltage( ) during short load spikes and normal load, so the
Impedance Track™ algorithm can calculate remaining capacity for pulsed loads. It is not recommended to
change this value.
Batt Insert Delay, Sleep Insert Delay
The Batt Insert Delay setting delays the bq27510-G2 detection process after battery insertion. Sleep Insert Delay
specifies the delay before the gauge enters Sleep Mode after battery insertion. For proper operation, set Sleep
Insert Delay greater than Batt Insert Delay. For example, with Batt Insert Delay = 10 ≤ (10,000ms) and Sleep
Insert Delay = 15 s, the bq27510-G2 does not enter SLEEP mode before 5 seconds after the battery detection.
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