SMB135 View Datasheet(PDF) - Summit Microelectronics
Part Name
Description
Manufacturer
SMB135
Summit Microelectronics
SMB135 Datasheet PDF : 34 Pages
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APPLICATIONS INFORMATION
DEVICE OPERATION
The SMB135 is a fully programmable battery charger
for single-cell Li-Ion and Li-Polymer battery packs. The
device’s high-efficiency, switch-mode operation
reduces heat dissipation and allows for higher current
capability for a given package size. The SMB135
provides four main charging phases: trickle-charge,
pre-conditioning (pre-charge), constant (fast-charge)
current and constant voltage. The overall system
accuracy of the SMB135 is 1%, allowing for a higher
capacity utilization versus other conventional solutions.
Furthermore, the main battery charging parameters are
programmable, allowing for high design flexibility and
sophisticated battery management.
Power Supply
The SMB135 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 Under-Voltage (UVLO) and Over-Voltage Lockout
(OVLO) circuits, which prevent the charger from turning
on when the voltage at this node is less than the UVLO
threshold (+3.5V), or greater than the OVLO threshold
(+7.0V). The IN pin also supplies an internal +2.5V
VDD regulator, filtered by an external capacitor
attached between the VDDCAP pin and ground; this
filtered voltage is then used as an internal VDD supply.
When the input supply is removed, the SMB135 enters
a low-power shutdown mode, exhibiting a very low
discharge leakage current (2µA), thereby extending
battery life.
Pre-qualification Mode
When an external wall adaptor or a USB cable is
connected, the SMB135 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, lower than the OVLO threshold and
130mV greater than the battery voltage; the ENABLE
input needs to be asserted or the appropriate I2C
command needs to be asserted; and the cell
temperature needs to be within the specified
temperature limits for the charging cycle to start. The
pre-qualification parameters are continuously monitored
and charge cycle is suspended when one of them is
outside the limits.
Trickle-charge Mode
Once all pre-qualification conditions are met, the device
checks the battery voltage to decide if trickle-charging
is required (Figure 3). If the battery voltage is below
approximately 2.0V, a charging current of 10mA
(typical) is applied on the battery cell. This allows the
SMB135 to reset the protection circuit in the battery
SMB135
pack and bring the battery voltage to a higher level
without compromising safety.
Pre-charge Mode
Once the battery voltage crosses the 2.0V level, the
SMB135 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 in 12.5mA steps, assuming a sense
resistor of 100mΩ (Register 00h). The SMB135
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).
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 either the
USB500/100 input (see below) or the corresponding
register. The fast charge current is programmable from
47.5mA to 525mA (16 steps), assuming a sense
resistor of 100mΩ (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 +4.00V to +4.62V in
20mV steps and is ±1% accurate over the 0°C to +70°C
temperature range. The higher float voltage settings of
the SMB135 enable the charging of modern battery
packs with a required float voltage of 4.3V, 4.4V, and
4.5V. Furthermore, the ability to dynamically adjust the
float voltage allows the implementation of sophisticated
battery charging and control algorithms.
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 130mA in 15mA steps,
assuming a sense resistor of 100mΩ (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).
Summit Microelectronics, Inc
2106 3.1 11/4/2008
13
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