LTC4015_15 Datasheet, PDF(37/76 Page) Linear Technology – Multichemistry Buck Battery Charger Controller with Digital Telemetry System

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LTC4015_15 Datasheet, PDF (37/76 Pages) Linear Technology – Multichemistry Buck Battery Charger Controller with Digital Telemetry System

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LTC4015

Operation

Constant-Current/Constant-Voltage (CC-CV) Charge:

In CC-CV charging phase, the LTC4015 prevents the

battery voltage from falling below the charge voltage level,

as determined by VCHARGE_SETTING, unless one of the

following conditions occurs:

a) The battery charge current ICHG reaches the target set

by ICHARGE_TARGET, indicated by constant_current=1

b) Input current limit (IIN_LIMIT_SETTING) is reached,

indicated by iin_limit_active=1

c) The UVCLFB pin voltage falls to the undervoltage current

limit (VIN_UVCL_SETTING), indicated by vin_uvcl_ac-

tive = 1

If either the input current limit or the input undervoltage

current limit is activated, the LTC4015 will limit charge

current and will attempt to regulate at the input current

limit or input undervoltage limit, as permitted by the input

source and system load. There is no termination in the

charging algorithm for lead-acid; the charger will remain

in CV mode as long as input power is available.

Equalization Charge:

If a rising edge is detected on the EQ pin (as reported by the

equalize_req bit), the LTC4015 will perform an equalization

charge when the charge voltage is reached (constant-

voltage = 1) in constant-current/constant-voltage (CC-CV)

charge phase. In equalization charging phase, the LTC4015

charges the battery at a constant-current ICHG, with a target

set by ICHARGE_TARGET and RSNSB, unless one of the

following conditions occurs:

(a) The battery voltage reaches the equalization

target voltage (as determined by VCHARGE_

SETTING+VEQUALIZE_DELTA, limited to a maximum

of 2.6V/cell), indicated by constant_voltage=1,

(b) Input current limit (IIN_LIMIT_SETTING) is reached,

indicated by iin_limit_active=1,or

limit (VIN_UVCL_SETTING), indicated by vin_uvcl_ac-

tive=1.

If either the input current limit or the input undervoltage

current limit is activated, the LTC4015 will limit charge

current and will attempt to regulate at the input current

limit or input undervoltage limit, as permitted by the input

source and system load. Equalize charge phase runs until

EQUALIZE_TIMER reaches EQUALIZE_TIME, at which time

the LTC4015 returns to constant-current/constant-voltage

(CC-CV) charge phase.

The EQ pin is rising edge triggered, it must remain high

through the duration of the equalize phase. The EQ pin

must be de-asserted and re-asserted to begin another

equalization charge.

VIN Input Power Removal/SUSPEND_CHARGER/

System Fault Response

If, at any time, the input voltage on the VIN pin falls to within

100mV of the BATSENS pin voltage, or suspend_charger is

written to 1 via the serial port, or if a system fault condition

occurs (VIN overvoltage, low 2P5VCC voltage, low INTVCC

voltage, low DRVCC voltage, thermal shutdown, missing

RT resistor, or invalid combination of CELLS pins), the

LTC4015 suspends charging and reports charger_sus-

pended = 1.

Battery Series Resistance (BSR) Measurement

The LTC4015 can optionally measure the series resistance

of the battery. If run_bsr is set to 1 the LTC4015

momentarily suspends the battery charger and calculates

the battery series resistance. The per cell resistance

value is reported in the BSR register and the change in

charge current is reported in the ICHARGE_BSR register

via the serial port. The battery series resistance value is

proportional to the charge current sense resistor, RSNSB,

that the resistance reported in the BSR register must be

multiplied by the total number of cells to calculate total

battery series resistance. The higher ICHARGE_BSR

(charge current) when a BSR measurement is requested,

the more accurate the BSR measurement will be. Very

low values of ICHARGE_BSR may significantly impact the

accuracy of the BSR measurement. Setting run_bsr to a

1 will not turn the charger on, if the charger is suspended

For more information www.linear.com/LTC4015

4015f

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