LTC4162EUFD-FST#PBF datasheet(16/52 Pages) AD

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LTC4162-F

Rev A

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OPERATION

the external MOSFETs will be enabled at a time. If VIN is

more than 150mV above BATSENS+, the MOSFET from

the input to the system load will be enabled and the one

from the system load to BATSENS+ will block conduction

preventing overcharging of the battery. If VIN falls more

than 20mV below BATSENS+ the MOSFET from the input

supply to the system load will be disabled preventing

reverse conduction and the MOSFET from BATSENS+ to

the system load will be enabled powering downstream

circuitry from the battery. It is important not to back drive

VOUT as one or the other of the power path MOSFETs will

always be enabled.

Step Down Switching Battery Charger

The LTC4162’s battery charger is based on a very efficient

synchronous step down switching regulator. As with any

modern battery charger, the LTC4162 incorporates both

constant-current and constant-voltage feedback control

loops to prevent overcharging. The switching charger can

charge either a single cell or a battery of up to nine series

lithium iron phosphate cells.

Normal charging begins with a constant current until the

battery reaches its target voltage. The charge current is

determined by the combination of the sense resistor,

RSNSB, placed in series with the inductor and the servo

control voltage set by either icharge_jeita_2 through

icharge_jeita_6 with en_jeita set or just charge_cur-

rent_setting if en_jeita is cleared. An internal soft-start

algorithm ramps up the charge current setting from zero

to its present setting. Once the battery voltage reaches the

programmed voltage limit the constant-current control

loop hands off to the constant-voltage control loop. The

final battery voltage is set with the combination of either

vcharge_jeita_2 through vcharge_jeita_6 with en_jeita

set or with just vcharge_setting if en_jeita is cleared. The

cell_count, controlled by the CELLS0 and CELLS1 pins,

is a charge voltage multiplier so that multiple series cells

can be charged.

If en_jeita is set, the charge current is given by the ex-

pression:

ICHARGE = (icharge _ jeita _ x + 1)

1mV

RSNSB

whereicharge_jeita_2throughicharge_jeita_6eachrange

from 0 to 31.

If en_jeita is not set:

ICHARGE = (charge _ current _ setting+ 1)

1mV

RSNSB

where charge_current_setting ranges from 0 to 31.

If en_jeita is set, the charge voltage is given by the ex-

pression:

VCHARGE = (3.4125V + 12.5mV • vcharge_jeita_x) •

cell_count

where vcharge_jeita_2 through vcharge_jeita_6 each

range from 0 to 31.

If en_jeita is not set:

VCHARGE = (3.4125V + 12.5mV • vcharge_setting) •

cell_count

where vcharge_setting ranges from 0 to 31.

Beyond the conventional constant-current and constant-

voltage control loops, the LTC4162 also has the ability to

monitor and control both input current and input voltage,

regulating battery charge power based on any one of these

four control loops. Power limit is prioritized based on the

lowestset-pointofthegroup.Forexample,ifthecombined

system load plus battery charge current is large enough

to cause the switching charger to reach the programmed

inputcurrentlimit,theinputcurrentlimitwillreducecharge

current to limit the voltage across the input sense resistor,

RSNSI, to the iin_limit_target. Even if the charge current

is programmed to exceed the allowable input current, the

input current due to charge current will not be violated;

the charger will reduce its current as needed. Similarly,

the input voltage limit loop, controlled by input_under-

voltage_setting, can be used to prevent resistive power

sources such as a solar panel from dragging the input

voltage down below its under-voltage lockout level.

Only target values can be programmed with the I2C port.

TheLTC4162usesthetargetvaluesasastartingpointfrom

which the charging algorithms calculate the actual values

to be applied to the DACs to support functions such as

LTC4162EUFD-FST#PBF Datasheet(PDF) 16 Page - Analog Devices

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