Datasheet

LM3658
www.ti.com SNVS328E –MAY 2005–REVISED MARCH 2007
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,
triggering 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 1. “ON”
means that STATx pin is pulled low as its pull-down transistor is turned on, representing a logic 0.
Table 1. Status Pins Summary
STAT1 STAT2 Condition
OFF OFF Power-Down, charging is suspended or
interrupted
ON OFF Pre-qualification mode, CC and CV
charging, Top-off mode
OFF ON Charge is completed
ON ON Bad battery (Safety timer expired), or LDO
mode
SAFETY TIMERS
In order to prevent endless charging of the battery, which can cause damage to the battery, there are three
safety timers that forcefully terminate charging if the charging mode is not completed within the time allowed.
Pre-Qualification Timer (T
PREQUAL
)
The pre-qualification timer starts with the initiation of the pre-qualification mode and allows 30 minutes to
transition from pre-qualification to full rate charging. If the battery voltage does not reach V
FULL_RATE
in 30
minutes, charging stops and status pins STAT1 and STAT2 both turn on to indicate a bad battery status.
Copyright © 2005–2007, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Links: LM3658