SMB218 View Datasheet(PDF) - Summit Microelectronics

Part Name

Description

Manufacturer

SMB218

Six-Channel Programmable DC-DC Power Managers with Battery Charger

Summit Microelectronics 

PLEASE NOTE: The SMB118 has entered End-of-Life.

SMB118/218

APPLICATIONS INFORMATION (CONTINUED)

Battery charging is initiated by the detection a DC

voltage on the DOCK_DC input. When the voltage on

DOCK_DC exceeds the programmed minimum

threshold voltage, the DC_IN pin will be asserted

indicating the successful connection of a charging

input.

Once the charging voltage exceeds the DOCK_DC

threshold voltage, the SMB118 will be powered from

the DOCK_DC pin. Once the voltage on DOCK_DC is

above the programmed setting, battery charging will

automatically commence. However, a programmable

option allows the user to prevent battery charging until

an I2C command has been issued. The SHDN pin is

bypassed once voltage is sensed on the DOCK_DC

pin.

TRICKLE CHARGE

Once all pre-qualification conditions are met, the

devices check the BSENSE voltage to decide if trickle

charging is required. If the battery voltage is below

approximately 2.0V, a charging current of 2mA (typical)

is applied on the battery cell. This allows the SMB118

and SMB218 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

SMB118 and SMB218 will begin to pre-charge the

battery to safely charge the deeply discharged cells.

The device stays in this mode until the voltage on

BSENSE input is above the programmed pre-charge

threshold voltage. The pre-charge threshold voltage is

programmable from 2.5V to 3.2V in 100mV increments.

The pre-charge current is programmable from 25 to

250mA, in 15mA increments.

FAST-CHARGE MODE

and 145mA, assuming a 100mΩ sense resistor. A

programmable option allows the Taper Charge mode to

be bypassed and the battery charging to be completed

once the final float voltage has been reached.

CURRENT SCALING

All charging currents are determined by measuring the

voltage across the battery current sense resistor. All

programmable currents are based on the use of a

100mΩ sense resistor. Currents can be increased or

decreased by scaling the current sense resistor. For

example, a 50mΩ sense resistor will scale the charging

current by a factor of two, while using a 200mΩ resistor

will scale the charging current by one half.

TEMPERATURE MONITORING

To inhibit charging when the battery temperature is

outside normal operating range a temperature sensing

input is provided.

The battery temperature is measured by sensing the

voltage between the TSENSE pin and ground. The

voltage is created by injecting a current into the parallel

combination of Negative Temperature Coefficient

(NTC) thermistor and a resistor. As the temperature

changes, the resistance of the thermistor changes

creating a voltage proportional to temperature. 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.

The temperature coefficient or Beta (Β) of the

thermistor must be as close to 4400 as possible to

achieve the maximum temperature accuracy.

After the pre-charge threshold voltage has been

exceeded, the battery charging current will be

increased from the pre-charge current to the fast-

charge current. The fast-charge current is

programmable from 100mA to 1A, in 60mA

increments. The battery will be charged with the fast-

charge current until the battery voltage exceeds the

final float voltage.

NTC THERMISTOR

10K

25K

100K

RESISTANCE

24.9K

61.9K

249K

TAPER CHARGE MODE

Once the final float voltage has been reached, the

battery charger will enter a constant voltage taper

charging mode, in which the battery voltage is held at

the final float voltage. The taper charging mode will

continue until the charge current drops below the

termination current threshold. The termination current

threshold is programmable at 100mA, 115mA, 130mA

Table 1: NTC values and associated parallel

resistances.

If the temperature limits are exceeded, battery charging

will be suspend until the battery voltage has fallen

within the safe operating range.. The over temperature

limit is programmable from 30°C to 65°C in 5°C

Summit Microelectronics, Inc

2107 3.0 10/15/2008

22

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