SMB239
APPLICATIONS INFORMATION (CONTINUED)
Automatic Battery Recharge
programmable EEPROM, found in Registers 00-07.
Once the device has been configured correctly, the
EEPROM may be locked, preventing any further
changes. Additionally, these registers may also be
configured so that they may be updated in RAM
(volatile), even if the underlying EEPROM is locked.
This feature is useful if it is desired to actively manage
the charging profile without making changes to the non-
volatile defaults. Use Register 0E to control locking
and volatile access. Before writing to Registers 00-07
in a volatile manner, Register 31[7] must first be set
high.
The SMB239 allows the battery to be automatically
recharged (topped off) when the battery voltage falls by
a
value of VRECH (115mV typical) below the
programmed float voltage. Provided that the input
power supply is still present, charging remains enabled
(I2C command) and all the pre-qualification parameters
are still met, a new charging cycle will be initiated. This
ensures that the battery capacity remains high, without
the need to manually re-start a charging cycle. The
automatic battery recharging can be disabled if not
required by the application (Register 03h).
FAULT and STATUS Indicators
USB500/100
A large number of battery charging conditions and
parameters are monitored and corresponding fault and
status indications are available to the user via the I2C
compatible registers. These include the following:
USB500/100 allows the user to select a maximum fast
charge current of 87mA or 525mA. The USB500/100
functionality is controlled over the I2C interface,
allowing for full software control of charge current
levels. This function is accomplished via register 31 bit
3, when Register 7 bit 0 is programmed high.
When the USB500 mode is selected, the charge
current level may be as high as 525mA. When the
USB100 mode is selected, the charge current level is
limited to 87mA. In all cases, a lower register value
setting will impose an overriding current limit.
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Charging status
Safety timer timeout
Over-temperature alarm
Under-temperature alarm
Over-voltage alarm
Under-voltage alarm
Missing battery detection
Safety Timers
The integrated safety timers provide protection in case
of a defective battery pack. The pre-charge timer starts
after the pre-qualification check is completed and
resets when the transition to the constant current mode
happens. At that point, the fast charge timer is initiated.
The fast charge timer expires and charge cycle is
terminated if the termination current level is not reached
within the pre-determined duration. Each safety timer
has three programmable timeout periods, which
eliminates the need for external timing capacitors and
allows for maximum design flexibility. In addition, each
timer can be disabled by the appropriate bit selection in
Register 05h.
Thermal Monitor
A temperature sensing I/O (THERM) is provided to
prevent excessive battery temperatures during
charging. The battery temperature is measured by
sensing the voltage between the THERM pin and
ground. The voltage is created by injecting a current
into the parallel combination of Negative Temperature
Coefficient (NTC) thermistor and a resistor. This
voltage is then compared to two predetermined
voltages representing the maximum and minimum
temperature settings of the battery. The purpose of the
resistor in parallel to the NTC thermistor is to linearize
the resistance of the thermistor. Table 1, shows the 1%
resistor that should be placed in parallel with the
corresponding thermistor.
If the temperature limits are exceeded, battery charging
will be suspended until the temperature level has fallen
within the safe operating range. The over-temperature
limit is programmable from 30°C to 65°C, and the
under-temperature limit is programmable from −20°C to
15°C, each in 5°C increments using Register 04h. In
addition, the user can easily select the required bias
current, based on the value of the negative temperature
coefficient (NTC) thermistor located in the battery pack:
10k, 25k, 100k (Register 04h). Disabling the thermal
monitor is also possible by selecting the appropriate
bits in Register 04h.
STAT Output
The STAT is an open-drain output that indicates battery
charge status. STAT has two modes of operation, as
determined by Register 05h[7]: in Mode 0, STAT is
asserted low whenever the battery is charging and de-
asserted at all other times; in Mode 1, STAT is de-
asserted when the charger is disabled, blinks during
charging, and remains continuously asserted when the
charge cycle has completed. A pull-up resistor should
be applied on this pin for interfacing to a microcontroller
or other logic IC.
Programmable Battery Charging
A unique feature of the SMB239 is the ability to modify
all of the important charger parameters via internally
Summit Microelectronics, Inc
2129 3.0 2/23/2009
12
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
