LTC4012 datasheet(24/52 Pages) AD

24 / 52 page

LTC4162-L

Rev A

For more information www.analog.com

OPERATION

Constant-Current Charging

Whenthebatteryvoltageisabove2.85Vpercell_count,the

charger will attempt to deliver either (icharge_jeita_x + 1)

• 1mV/RSNSBwithen_jeitaor(charge_current_setting+1)

• 1mV/RSNSB without en_jeita in constant-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

When the switching battery charger is enabled at an el-

evated 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 regu-

lation algorithm achieves this by enforcing a maximum

icharge_dac setting which drops linearly from 31 to 0 as

die_tempincreasesfromthermal_reg_start_temp(default

120°C) to thermal_reg_end_temp (default 125°C). When

the thermal regulation algorithm is active, charge_status

becomes thermal_reg_active. A thermal_reg_active_alert

can be set 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

(3.8125V+12.5mV • vcharge_jeita_x) • cell_countwithen_

jeita or (3.8125V + 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

LTC4012 датащи(PDF) 24 Page - Analog Devices

LTC4012 датащи(HTML) 24 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

датащи скачать

ссылки URL