LTC4162EUFD-FST#PBF datasheet(24/52 Pages) AD

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LTC4162-F

Rev A

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OPERATION

Constant-Current Charging

The charger will attempt to deliver either (icharge_

jeita_x + 1) • 1mV/RSNSB with en_jeita or (charge_cur-

rent_setting+1)• 1mV/RSNSBwithouten_jeitainconstant-

current mode where icharge_jeita_x or charge_current_

setting ranges from 0 to 31. For example, A 10mΩ resistor

between CPS and CSN would give an upper limit charge

current of 3.2A. Depending on available input power and

external load conditions, the battery charger may not be

able to charge at the full programmed rate. An alternate

control loop such as the input current limit loop or input

voltage limit loop may be in force and only partial power

will be available to charge the battery. If input current limit

is reached, for instance, the system load will be prioritized

over the battery charge current. When system loads are

light, battery charge current will be maximized and could

be as high as the value programmed by icharge_jeita_x

or charge_current_setting.

The charge current programming resistor, RSNSB, should

always be set to match the capacity of the battery with-

out regard to source or load limitations from any other

control loop. The multiple control-loop architecture of

the LTC4162 will correct for any discrepancies, always

optimizing transfer of power to the battery and the load.

Thermal Regulation

Whentheswitchingbatterychargerisenabledatanelevated

ambient temperature, LTC4162 self heating may push its

junction temperature to an unacceptable level. To prevent

overheating the LTC4162 monitors its own die_temp and

automatically reduces the icharge_dac to limit power

dissipation. The differential servo voltage at CSP to CSN

can drop to as low as 1mV giving about 3% (1/32) of the

maximum charge current. The thermal regulation algo-

rithm achieves this by enforcing a maximum icharge_dac

setting which drops linearly from 31 to 0 as die_temp

increasesfromthermal_reg_start_temp(default120°C)to

thermal_reg_end_temp(default125°C).Whenthethermal

regulation algorithm is active, charge_status becomes

thermal_reg_active.Athermal_reg_active_alertcanbeset

with en_thermal_reg_active_alert and cleared by writing

either back to 0. Thermal regulation can be programmed

to any temperature within the LTC4162's operating range.

Constant-Voltage Charging

Once the BATSENS+ voltage reaches the programmed

charging voltage the switching regulator will reduce its

output power and hold the battery voltage steady at either

(3.4125V+12.5mV • vcharge_jeita_x) • cell_countwithen_

jeita or (3.4125V + 12.5mV • vcharge_setting) • cell_count

without en_jeita where vcharge_jeita_x and vcharge_set-

ting each range from 0 to 31. In constant voltage mode

the charge current will decrease naturally toward zero

providing inherently safe operation by preventing the

battery from being over charged. Multiple charge voltage

settings are available for final top-off voltage selection via

vcharge_jeita_x with en_jeita or vcharge_setting without

en_jeita. While charge voltage trade-offs can be made to

preserve battery life or maximize capacity, it is not pos-

sible for the LTC4162 to be set to a charge voltage that

is dangerously high or inconsistent with a Lithium-Ion/

Polymer Battery.

Note that charge_current_setting and vcharge_setting do

notdirectlycontroltheicharge_dacandvcharge_dac.They

are only target values. For example, if the JEITA Tempera-

ture Controlled Charging system is enabled (en_jeita = 1),

the DACs will be controlled by this user programmable

system (i.e. icharge_jeita_2 through icharge_jeita_6,

vcharge_jeita_2 through vcharge_jeita_6).

Basic Temperature Controlled Charging

The LTC4162 provides temperature controlled charging if

a grounded thermistor and a bias resistor are connected

to the NTCBIAS and NTC pins and en_jeita is set to 0.

Charging is paused if thermistor_voltage rises above

jeita_t1 (0°C) or falls below jeita_t6 (60°C). Recall that

thermistors have a negative temperature coefficient so

higher temperatures will read lower thermistor_voltage

and vice versa. If charging is not suspended, the charg-

ing voltage and current will follow vcharge_setting and

charge_current_setting respectively.

The default upper and lower limits are based on a thermis-

tor with a β25/85 value of 3490K, such as provided by a

Vishay NTCS0402E3103FLT. This thermistor was chosen

specifically because of its weak temperature characteristic

relative to other thermistors. Stronger thermistors can

LTC4162EUFD-FST#PBF Datasheet(PDF) 24 Page - Analog Devices

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