LT8491 datasheet(21/82 Pages) AD

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LT8491

Rev. 0

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OPERATION

Configure VBAT for Stages 0, 1 and 3 section. Stage 1 is

often referred to as bulk charging in the battery charging

community. However, this stage will continue to be called

Stage 1 for the remainder of this document. Stage 1 charg-

ing is indicated in the STAT_CHARGER register when the

CHRG_STAGE bits are 001b and the CHRG_LOGIC_ON

bit is 1.

Stage 2: Constant Voltage

In Stage 2, the LT8491 charges the battery to a constant

voltage (VS2). This constant voltage stage is indicated

for battery voltages above 98% (typical) of the Stage 2

voltage. Stage 2 is often referred to as float charging for

lithium-ion batteries and absorption charging for lead-

acid batteries. To avoid confusion, this stage is referred

to as Stage 2 for the remainder of this document. Stage 2

charging is indicated in the STAT_CHARGER register

when the CHRG_STAGE bits are 010b and the CHRG_

LOGIC_ON bit is 1.

Charging in Stage 2 typically continues until the output

current (IOUT) falls below C/10. Options are available to

configure how the charger proceeds from Stage 2. These

options include:

• Terminate charging when IOUT < C/10

• Terminate when the Stage 2 timer expires

• Proceed to Stage 3 when IOUT < C/10

• Continue charging in Stage 2 indefinitely

Footnotes in Figure 8 indicate the respective I2C configu-

ration registers for these options.

Stage 3: (Optional) Reduced Constant Voltage

Stage 3 is optionally enabled in the CFG_CHRG_MISC

a reduced constant voltage. Stage 3 is often referred to

as float charging for lead-acid batteries. It will continue

to be called Stage 3 for the remainder of this document.

Stage 3 charging is indicated in the STAT_CHARGER

CHRG_LOGIC_ON bit is 1.

Done Charging

When done charging, the power stage is disabled, and

charging is complete. This is indicated in the STAT_

CHARGER register when the CHRG_STAGE bits are 100b

and the CHRG_LOGIC_ON bit is 1. Telemetry acquisition

generally continues although some telemetry, related to

the battery side of the charger, may be limited as dis-

cussed in the Telemetry: Acquisition section. In addition,

although some telemetry continues to be acquired, no

charging faults will be reported. Restarting the charging,

when done charging, can be done in four ways:

• The charging can be restarted by toggling the control

charger enable bit low to high. See the CTRL_CHRG_

EN register description.

• The charger can be configured to restart automatically

under various conditions. See the Configure Automatic

Restart section.

• The charger can be reset by cycling the power.

• Issuing a restart chip command while CTRL_CHRG_EN

is cleared, will also restart the charger if CFG_INIT_

CHRG_EN is set. See the CTRL_RESTART_CHIP reg-

ister description.

Charging Faults

The LT8491 periodically monitors for the following

fault conditions, on a priority basis, while the charging

logic is on (STAT_CHARGER→CHRG_LOGIC_ON=1)

and the charger isn’t in an input UVLO condition

(STAT_SUPPLY→VIN_UVLO=0):

• VBAT too low for charging

• Battery temperature too low for charging

• Battery temperature too high for charging

• Battery disconnected

• Stage timer expired and configured to be a fault, indi-

cating that charging took too much time

These faults are reported in the STAT_CHRG_FAULTS

source is provided in the register’s data sheet section.

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