LM3658 Datasheet, PDF (9/13 Pages) National Semiconductor (TI) – Dual Source USB/AC Li Chemistry Charger IC for Portable Applications

LM3658 Operation Description
(Continued)
TABLE 3. Status Pins Summary
STAT1
OFF
ON
OFF
ON
STAT2
OFF
OFF
ON
ON
Condition
Power-Down, charging is
suspended or interrupted
Pre-qualification mode, CC and CV
charging, Top-off mode
Charge is completed
Bad battery (Safety timer expired),
or LDO mode
If the TS pin is not used in the application, it should be
connected to GND through 10kΩ pulldown resistor.
When the TS pin is left floating (battery removal), then the
charger will be disabled as the TS voltage exceeds the upper
temperature limit.
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.
Charger Timer (T_CHG)
The charge timer starts with the initiation of full-rate charging
and has a duration of 5 hours for the LM3658. If the charge
current does not reach EOC, charging stops and STAT1 and
STAT2 both turn on to indicate a bad battery status. Once
the charge control declares a bad battery, removing the input
source is the only means to clear the bad battery status.
Top-Off Timer (T_TOPOFF)
Once the charger successfully completes constant current
constant voltage charging, it enters top-off mode and starts
T_TOPOFF timer. Topoff lasts 30 minutes for the LM3658.
During top-off, charging stops when T_TOPOFF reaches its
count or when I_CHG reaches 2.5% of the full-rate charge
current. There is no time-out condition in top-off mode.
When charging is interrupted either by battery temperature
out of range or disabling the LM3658, the applicable safety
timer will store its count value for the duration of the inter-
ruption and subsequently resumes counting from its stored
count value when charging continues, only if the charger
resumes to the same operation mode it was in before the
interrupt.
BATTERY TEMPERATURE MONITORING (Suspend
Mode)
The LM3658 is equipped with a battery thermistor interface
to continuously monitor the battery temperature by measur-
ing the voltage between the T_S pin and ground. Charging is
allowed only if the battery temperature is within the accept-
able temperature range set by a pair of internal comparators
inside the LM3658. If the battery temperature is out of range,
STAT1 and STAT2 both turn off and charging is suspended.
Timer holds its count value.
The TS pin is only active during charging and draws no
current from the battery when no external power source is
present.
20128210
The LM3658 battery temperature feature is tailored to use
negative temperature coefficient (NTC) 103AT thermistors
with 10kΩ impedance. If alternative thermistors need to be
used in the system, supplemental external resistors are
needed to create a circuit with equivalent impedance.
20128211
DISABLING CHARGER (Charge Interrupt Mode)
Charging can be safely interrupted by pulling the EN_b pin
high and charging can resume upon pulling the EN_b pin
low. The enable pin can be permanently tied to GND with no
extra current consumption penalty during power down mode.
When the charger is disabled, timer holds its count value,
and STAT1 and STAT2 are both off.
INPUT/OUTPUT BYPASS CAPACITORS
Care should be taken to support the stability of the charge
system by connecting a 1 µF capacitor as close as possible
to the BATT pin. An input capacitor ranging from 1.0 µF–
10.0 µF must be connected to the CHG_IN and USBpwr
input pins. Low cost ceramic capacitors can be selected.
THERMAL PERFORMANCE OF THE LLP PACKAGE
The LM3658 is a monolithic device with integrated power
FETs. For that reason, it is important to pay special attention
to the thermal impedance of the LLP package and to the
PCB layout rules in order to maximize power dissipation of
the LLP package.
The LLP package is designed for enhanced thermal perfor-
mance and features an exposed die attach pad at the bottom
center of the package that creates a direct path to the PCB
for maximum power dissipation. Compared to the traditional
leaded packages where the die attach pad is embedded
inside the molding compound, the LLP reduces one layer in
the thermal path.
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