LP3910 datasheet(33/72 Pages) TI1

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LP3910

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SNVS481M – NOVEMBER 2006 – REVISED DECEMBER 2015

8.3.4.3 Thermal Charger Power FET Regulation

The internal power FET Q2 in the linear charger module is thermally regulated to the junction temperature of

115°C to ensure optimal charging of the battery. The charge current is limited by the charge current selected in

the charger control register but is also thermally limited to prevent the junction from overheating during high

charge currents at high ambient temperatures as the package power dissipation is limited.

Thermal regulation ensures maximum charge current and superior charge rate without exceeding the power

dissipation limits of LP3910 device.

8.3.4.4 Battery Charger Operating Modes

8.3.4.4.1

Pre-Qualification Mode

Lithium batteries cannot be subjected to a high current when the battery voltage is under a certain threshold,

otherwise the longevity of the battery would be compromised. Below this threshold of VFULLRATE, which typically

measures 2.85 V, the charger circuit supplies a pre-qualification charge current. If the wall adapter is charging

the battery, the charger circuit supplies a constant current of 10% of the programmed charge current. If the USB

is charging the battery, the charger circuit supplies a constant 50-mA charge current. When the battery voltage

reaches VFULL_RATE, the charger transitions from pre-qualification to full-rate charging. In pre-qualification mode,

the STAT2, STAT1, and STAT0 bits in the charger supervisory register are respectively low, low, high.

8.3.4.4.2

Full-Rate Charging Mode

The full-rate charge cycle is initiated following the successful completion of the pre-qualification mode. During

full-rate charging, the battery voltage steadily increases while charged with a CC. The three charger status bits

STAT2, STAT1, and STAT0 are respectively low, high, and low. The full-rate charge current is selected using the

charge control register, which defaults to 100 mA.

Charging Li-ion batteries at a rate of 1C is recommended (where C is the capacity of the battery). As an

example, it is recommended to charge a battery with a capacity of 800 mA at 800 mA, or 1C. Charging at a

higher rate may compromise the quality and lifetime of the battery.

8.3.4.4.3

Constant-Voltage (CV) Charging Mode

The battery voltage increases rapidly as a result of full-rate charging and once it reaches the programmable

termination voltage of either 4.1 V, 4.2 V or 4.38 V, the charger moves to constant-voltage charge mode. During

this mode, the charge current gradually decreases while the battery remains at the termination voltage. The

termination voltage can be selected to be either 4.1 V, 4.2 V or 4.38 V by programming bits D6 and D7 in the

Charger Control register to accommodate different battery chemistries. In CV charging mode, the Charge Control

Status bits STAT2, STAT1 and STAT0 are respectively logic 0, logic 1, and logic 1.

8.3.4.4.4

Top-Off Charging Mode

When the charge current reduces to the EOC threshold (programmable to 5% or 10% of programmed full rate

charge current), constant voltage charging continues for an additional 21 minute TOP-OFF time period. In TOP-

OFF charging mode, the Charge Control Status bits STAT2, STAT1 and STAT0 are respectively logic 1, logic 1

and logic 1. At the end of the TOP-OFF period, the charger transitions to Charge Cycle Complete.

8.3.4.4.5

Charge Cycle Complete

During charge cycle complete, the charger is automatically disabled, regardless of the state of the charge enable

bit. In charge cycle complete, the STAT2, STAT1 and STAT0 bits are respectively logic 1, logic 0, and logic 1.

When the battery voltage drops below the VRESTART threshold, charging resumes in full-rate charging mode.

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