LTC4015_15 Datasheet, PDF (49/76 Pages) Linear Technology – Multichemistry Buck Battery Charger Controller with Digital Telemetry System

LTC4015
Applications Information
The LTC4015 CHEM1 and CHEM0 pins are strapped to
select the chemistry algorithm. Upon initial power-up,
the serial port master writes suspend_charger=1, then
writes VCHARGE_SETTING, VABSORB_DELTA, MAX_
ABSORB_TIME, VEQUALIZE_DELTA, and EQUALIZE_TIME
based on the battery manufacturer’s recommendation for
charge voltage and time. The master writes NTC_RATIO_
LO_ALERT_LIMIT to the value of NTC_RATIO which
corresponds to the maximum safe charging temperature
for the battery pack and NTC thermistor, and writes
en_ntc_ratio_lo_alert = 1. The master then re-enables
the battery charger by writing suspend_charger=0. At
regular long intervals (for example, every 30 days) the
master optionally initiates an equalization charge by as-
serting the EQ pin.
If the thermistor temperature ever exceeds the level
corresponding to NTC_RATIO_LO_ALERT_LIMIT, the
LTC4015 pulls down the SMBALERT pin. The serial port
master then performs an ARA which confirms that the
LTC4015 is the source of the alert and causes the LTC4015
to release the SMBALERT pin. The master reads the
LIMIT_ALERTS register to confirm that ntc_ratio_lo_alert
is true. The master then writes suspend_charger=1 to
disable the battery charger.
Optionally, in order to detect when the battery temperature
has returned to a safe level for charging, the master writes
NTC_RATIO_HI_ALERT_LIMIT to a value corresponding
to 5°C below the maximum safe charging temperature of
the battery, and writes en_ntc_ratio_hi_alert=1. When the
thermistor temperature falls below this level, the LTC4015
generates a new SMBALERT for ntc_ratio_hi_alert=1,
which is again confirmed by the master. The master
then disables the alert by writing en_ntc_ratio_hi_alert=0,
clears ntc_ratio_lo_alert (by writing a 0 to that bit), then
re-enables the charger by writing suspend_charger=0.
See the sections Lead-Acid Battery Charge Algorithm,
Programmable Interrupt Controller, and Detailed Register
Descriptions for more details.
LTC4015 Digital System Usage Example 3: Battery
Charger State Monitoring
The serial port master writes en_charger_suspended_
alert=1 to generate an alert if the battery charger is ever
disabled (e.g. due to the removal of V_IN input power). If
V_IN input power is removed, the LTC4015 pulls down the
SMBALERT pin and sets the charger_suspended bit to 1.
After performing an ARA, the serial port master directs the
system to minimize battery drain (e.g. dimming displays,
powering down unnecessary functions, etc).
For more information www.linear.com/LTC4015
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