SMB239
APPLICATIONS INFORMATION
DEVICE OPERATION
2.0V, a charging current of 10mA (typical) is applied on
the battery cell. This allows the SMB239 to reset the
protection circuit in the battery pack and bring the
battery voltage to a higher level without compromising
safety.
The SMB239 is a fully programmable battery charger
for single-cell Li-Ion and Li-Polymer battery packs. The
device’s simple, linear-mode operation and ultra-small
package significantly reduce component count and
required board space. The SMB239 provides four main
charging phases: trickle-charge, pre-conditioning (pre-
charge), constant (fast-charge) current and constant
voltage. The overall system accuracy of the SMB239 is
1%, allowing for a higher capacity utilization versus
Pre-charge Mode
Once the battery voltage crosses the 2.0V level, the
SMB239 pre-charges the battery to safely charge the
deeply discharged cells (Figure 3). The pre-charge
(pre-conditioning) current is programmable from 25mA
to 212.5mA (Register 00h). The SMB239 remains in
this mode until the battery voltage reaches the pre-
charge to fast-charge voltage threshold (programmable
from +2.4V to +3.1V in 100mV steps). If the pre-charge
to fast-charge voltage threshold is not exceeded before
the pre-charge timer expires, the charge cycle is
terminated and a corresponding timeout fault signal is
asserted (“Pre-charge Timeout” in register 36h).
other conventional solutions.
The main battery
charging parameters are programmable, allowing for
high design flexibility and sophisticated battery
management. Furthermore, the SMB239 offers many
advanced protection features, allowing applications to
meet strict safety standards without the need for
additional cost and components.
Power Supply
The SMB239 can be powered from an input voltage
between +4.35 and +6.5 Volts applied between the IN
pin and ground. The voltage on the IN pin is monitored
by an Under-Voltage (UVLO) circuit, which prevents the
charger from turning on when the voltage at this node is
less than the UVLO threshold (+3.5V). The IN pin also
supplies an internal +2.5V VDD regulator, which is used
as an internal VDD supply. When the input supply is
removed, the SMB239 enters a low-power shutdown
mode, exhibiting a very low discharge leakage current
(2µA), thereby extending battery life.
Constant Current Mode
When the battery voltage exceeds the pre-charge to
fast-charge voltage threshold, the device enters the
constant current (fast charge) mode. During this mode,
the fast charge current level is set by the corresponding
register. The fast charge current is programmable from
47.5mA to 525mA (Register 00h).
Constant Voltage Mode
When the battery voltage reaches the pre-defined float
voltage, the fast-charge current starts diminishing. The
float voltage is programmable from +4.020V to +4.40V
in 20mV steps and is ±1% accurate over the +10°C to
+50°C temperature range. The higher float voltage
settings of the SMB239 enable the charging of modern
battery packs with a required float voltage of 4.3V, and
4.4V. Furthermore, the ability to dynamically adjust the
float voltage allows the implementation of sophisticated
battery charging and control algorithms.
Pre-qualification Mode
When an external wall adaptor or another type of power
source is connected, the SMB239 performs a series of
pre-qualification tests before initiating the first charge
cycle. The input voltage level needs to be higher than
the UVLO threshold, and 130mV greater than the
battery voltage; and the appropriate I2C command
(enable/disable) needs to be asserted. The pre-
qualification parameters are continuously monitored
and charge cycle is suspended when one of them is
outside the limits.
A device option exists (controlled by register 08h[5]) for
preventing charging initiation upon power cycling
unless the battery voltage is 200mV, 390mV or 550mV
(VCH) below the float voltage level. This prevents over-
stressing of the battery via continuous charging cycles
in systems with short run times and frequent power
cycling (IN power connect/disconnect).
Charge Completion
The charge cycle is considered complete when the
charge current reaches the programmed termination
current threshold. The termination current is
programmable from 25mA to 250mA (Register 01h). If
the termination current threshold is not met before the
fast-charge timer expires, the charge cycle is
terminated and a corresponding timeout fault signal is
asserted (“Fast-charge Timeout” in register 36h).
Trickle-charge Mode
Once all pre-qualification conditions are met, the device
checks the battery voltage to decide if trickle-charging
is required. If the battery voltage is below approximately
Summit Microelectronics, Inc
2129 3.0 2/23/2009
11
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
