LM3658 Datasheet, PDF (8/13 Pages) National Semiconductor (TI) – Dual Source USB/AC Li Chemistry Charger IC for Portable Applications

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_{OK_CHG} (V_BATT >
V_CC - V_{OK_CHG}). Power-Down mode shuts off the internal
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_BATT + V_{OK_CHG}, the charger will wake up. However,
charging will not be initiated unless the supply voltage
source exceeds the V_POR.
AUTOMATIC POWER SOURCE DETECTION
When the voltage of one of the power sources exceeds the
V_POR threshold, the LM3658 detects which power source is
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-
tion temperature of 120^oC to guarantee optimal charging of
the battery. At all times is the charge current limited by the
I_SET resistor setting, the USB 100 mA/500 mA selection, or
the 100^oC junction temperature of the LM3658. The charge
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_A is the ambient temperature and θ_JA is the thermal
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_{FULL_RATE}, the
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_PREQUAL timer. In this event, charging stops and STAT1 and
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_CHG starts
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_SET pin as
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_CHG starts
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_CHG continues
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_SET pin or the USB_sel pin. If Timer T_CHG
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_CHG reaches 2.5% of
the full-rate charge current or when T_TOPOFF times out,
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_TERM, a new full-rate charge cycle starts to replenish the
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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