LM3658 Operation Description

POWER-DOWN MODE

The LM3658 will power down automatically when the voltage

on the USBpwr or CHG_IN pin drops below the battery

voltage with an amount that is equal to V

V

power FETs as well as the open-drain pull-down transistors

on the status pins STAT1 and STAT2. The only current

consumed by the LM3658 is an ultra-low quiescent current

of 1 µA typical.

POWER-ON RESET

As soon as the voltage of one of the power sources rises

above V

charging will not be initiated unless the supply voltage

source exceeds the V

AUTOMATIC POWER SOURCE DETECTION

When the voltage of one of the power sources exceeds the

V

a valid charge supply. When both supply voltages are valid

and present, CHG_IN will automatically be selected over

USBpwr. The USBpwr will be the designated power source

only if no CHG_IN is present or when the voltage on the

CHG_IN pin is less than the battery voltage.

THERMAL POWER FET REGULATION

The internal power FETs are thermally regulated to the junc-

the battery. At all times is the charge current limited by the

I

current is therefore a function of the charge current settings,

the thermal conductivity of the package and the ambient

temperature as described in the following equation:

20128205

Where T

θ

resistance of the package. Thermal regulation guarantees

maximum charge current and superior charge rate without

exceeding the power dissipation limits of the LM3658.

PRE-QUALIFICATION MODE

During pre-qualification, STAT1 is on and STAT2 is off, and

the charger supplies a constant current of 50 mA to the

battery. When the battery voltage reaches V

charger transitions from pre-qualification to full-rate charg-

ing. The pre-qualification mode aborts when the battery

doesn’t reach V

FULL_RATE

within the time allowed in

T

STAT2 will both be on, indicating a bad battery condition.

CHG_IN FULL-RATE CHARGING MODE

The full-rate charge cycle is initiated following the successful

completion of the pre-qualification mode. Timer T

to count when the charger enters full-rate charging, with

STAT1 on and STAT2 off. When charging with an AC wall

adapter, the full-rate charge current is proportional to the

value of the resistor that is connected to the I

described in the following equation:

It is recommended to charge Li-Ion batteries at 1C rate,

where “C” is the capacity of the battery. As an example, it is

recommended to charge a 750 mAh battery at 750 mA, or

1C. Charging at a higher rate can cause damage to the

battery.

USBpwr FULL-RATE CHARGING MODE

The full-rate charge cycle is initiated following the successful

completion of the pre-qualification mode. Timer T

to count when the charger enters full-rate charging, with

STAT1 on and STAT2 off. If the USB bus provides the

charger supply, then the default full-rate charge current is

100 mA max unless the USB_sel pin is pulled high, which

sets the charge current to 500 mA max.

CONSTANT-VOLTAGE CHARGING MODE AND

END-OF-CHARGE (EOC) DETECTION

The battery voltage increases rapidly as a result of full-rate

charging and will reach the 4.2V termination voltage, trigger-

ing the constant-voltage charge cycle. Timer T

to count in this cycle. STAT1 is on and STAT2 is off. The

charge current gradually decreases during constant-voltage

charging until it reaches the End-Of-Charge (EOC), which is

equal to 10% of the full-rate current set either by the resistor

connected to the I

times out before EOC is reached, charging stops and STAT1

and STAT2 will both be on, indicating a bad battery condition.

TOP-OFF CHARGING MODE

Once EOC has been reached, a top-off cycle continues to

charge the battery. Timed top-off cycle provides optimal

battery capacity following a complete charge cycle. During

this cycle, charging terminates when I

the full-rate charge current or when T

whichever occurs first. STAT1 will turn off and STAT2 will turn

on once the top-off cycle completes successfully, indicating

that charging is done.

MAINTENANCE MODE

Maintenance mode begins immediately after the charger

successfully finishes the top-off cycle. In the maintenance

mode, the battery voltage is being monitored by the LM3658

continuously. If the battery voltage drops 200 mV below

V

battery. As this new full-rate charge cycle begins, STAT1 will

turn on and STAT2 will turn off, and all the timers will reset.

Refer to the LM3658 Flowchart.

CHARGE STATUS OUTPUTS

The LM3658 provides two open-drain outputs STAT1 and

STAT2 that can be connected to external LEDs or to General

Purpose I/O’s (GPIO) of a peripheral IC. All charge status of

the LM3658 is illustrated in Table 3. “ON” means that STATx

pin is pulled low as its pull-down transistor is turned on,

representing a logic 0.

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