SMB239 datasheet(12/30 Pages) SUMMIT

12 / 30 page

SMB239

Summit Microelectronics, Inc

2129 3.0 2/23/2009

Automatic Battery Recharge

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

2C 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).

USB500/100

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.

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

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

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.

FAULT and STATUS Indicators

A large number of battery charging conditions and

parameters are monitored and corresponding fault and

status indications are available to the user via the I

compatible registers. These include the following:

•

Charging status

•

Safety timer timeout

•

Over-temperature alarm

•

Under-temperature alarm

•

Over-voltage alarm

•

Under-voltage alarm

•

Missing battery detection

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

°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.

APPLICATIONS INFORMATION (CONTINUED)

SMB239 Datasheet(PDF) 12 Page - Summit Microelectronics, Inc.

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