SMB239 datasheet(11/30 Pages) SUMMIT

11 / 30 page

SMB239

Summit Microelectronics, Inc

2129 3.0 2/23/2009

APPLICATIONS INFORMATION

DEVICE OPERATION

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

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.

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).

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

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.

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).

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

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.

Charge Completion

The charge cycle is considered complete when the

charge current reaches the programmed termination

current

threshold.

The

termination

current

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).

SMB239 数据表(PDF) 11 Page - Summit Microelectronics, Inc.

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