AAT3685IWP-4.2-1-T1 Ver la hoja de datos (PDF) - Analog Technology Inc

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AAT3685IWP-4.2-1-T1

Lithium-Ion/Polymer Battery Charger

Analog Technology Inc 

BatteryManagerTM

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AAT3685

Lithium-Ion/Polymer Battery Charger

Charge Complete Voltage

Regulated Current

Preconditioning

Trickle Charge

Phase

Constant Current

Charge Phase

I = Max CC

Constant Voltage

Charge Phase

Constant Current Mode

Voltage Threshold

Trickle Charge and I = CC / 10

Termination Threshold

Figure 1: Current vs. Voltage Profile During Charging Phases.

Battery Preconditioning

Before the start of charging, the AAT3685 checks sev-

eral conditions in order to assure a safe charging envi-

ronment. The input supply must be above the minimum

operating voltage, or under-voltage lockout threshold

(VUVLO), for the charging sequence to begin. In addition,

the cell temperature, as reported by a thermistor con-

nected to the TS pin from the battery, must be within the

proper window for safe charging. When these conditions

have been met and a battery is connected to the BAT

pin, the AAT3685 checks the state of the battery. If the

cell voltage is below the Preconditioning Voltage Threshold

(VMIN), the AAT3685 begins preconditioning the cell.

The battery preconditioning trickle charge current is

equal to the fast charge constant current divided by 10.

For example, if the programmed fast charge current is

500mA, then the preconditioning mode (trickle charge)

current will be 50mA. Cell preconditioning is a safety pre-

caution for a deeply discharged battery and also aids in

limiting power dissipation in the pass transistor when the

voltage across the device is at the greatest potential.

Fast Charge / Constant Current Charging

Battery cell preconditioning continues until the voltage

on the BAT pin exceeds the Preconditioning Voltage

Threshold (VMIN). At this point, the AAT3685 begins the

constant current fast charging phase. The fast charge

constant current (ICC) amplitude is determined by the

selected charge mode SETH or SETL and is programmed

by the user via the RSETH and RSETL resistors. The AAT3685

remains in constant current charge mode until the bat-

tery reaches the voltage regulation point, VBAT.

Constant Voltage Charging

The system transitions to a constant voltage charging

mode when the battery voltage reaches output charge

regulation threshold (VBAT) during the constant current,

fast charge phase. The regulation voltage level is fac-

tory programmed to 4.2V ( 1%). The charge current in

the constant voltage mode drops as the battery cell

under charge reaches its maximum capacity.

End of Charge Cycle Termination

and Recharge Sequence

When the charge current drops to 7.5% of the pro-

grammed fast charge current level in the constant volt-

age mode, the device terminates charging and goes into

a sleep state. The charger will remain in a sleep state

until the battery voltage decreases to a level below the

battery recharge voltage threshold (VRCH).

When the input supply is disconnected, the charger will

also automatically enter power-saving sleep mode. Only

consuming an ultra-low 0.3μA in sleep mode (1μA for

AAT3685-1), the AAT3685 minimizes battery drain when

it is not charging. This feature is particularly useful in

applications where the input supply level may fall below

the battery charge or under-voltage lockout level. In

such cases where the AAT3685 input voltage drops, the

device will enter the sleep mode and automatically

resume charging once the input supply has recovered

from its fault condition.

3685.2007.12.1.4

www.analogictech.com

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