LTC4015_15 Datasheet, PDF (38/76 Pages) Linear Technology – Multichemistry Buck Battery Charger Controller with Digital Telemetry System

LTC4015
Operation
or in a termination state. Setting run_bsr = 1 results in the
BSR measurement request being queued and run after the
soft-start of the next charge cycle.
Lead-Acid Temperature Compensated Charging (en_
lead_acid_temp_comp=1)
The LTC4015 uses a –3.65 mV/°C per cell V_CHARGE
temperature compensation when using a thermistor with a
β value of 3490K similar to a Vishay NTCS0402E3103FLT
or NTHS0402N02N1002JE thermistor. When en_lead_
acid_temp_comp=1, the registers VCHARGE_SETTING,
VABSORB_DELTA, and VEQUALIZE_DELTA control the
25°C value of VCHARGE_DAC. At other temperatures, the
value of VCHARGE_DAC is adjusted based on NTC_RATIO,
to produce the temperature profile shown in Figure 9. In
effect, the temperature profile is shifted up or down by
increasing or decreasing the values of VCHARGE_SETTING,
VABSORB_DELTA, and VEQUALIZE_DELTA, but the slope
of the temperature compensation response is not directly
programmable.
2.7
CC-CV
2.6
ABSORB
EQUALIZE
2.5
2.4
2.3
2.2
2.1
2.0
1.9
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
4015 F09
Figure 9. Lead-Acid Temperature Profile
The LTC4015 limits lead-acid charge voltage to 2V to 2.6V/
cell regardless of battery temperature in CC-CV, Absorb
and equalize modes. VABSORB_DELTA is an adder to
VCHARGE_SETTING in absorb mode. VEQUALIZE_DELTA
is an adder to VCHARGE_SETTING in equalize mode.
At 25°C the default charge voltage is 2.2 V/cell. Using –3.65
mV/°C per cell, V_CHARGE will reach its minimum of 2.0V/
cell at a temperature of 80°C. Similarly, V_CHARGE reaches
its maximum of 2.6V/cell at a temperature of –85°C.
The default VABSORB_DELTA value is 0x15 (21 decimal).
This translates to an absorb voltage of 2.4V/cell at 25°C.
The default VEQUALIZE_DELTA value is 0x2A (42 decimal).
This translates to an equalize voltage of 2.6V/cell at 25°C.
Temperature compensation is active over a NTC_RATIO
range of 21437 to 912, which corresponds to an ap-
proximate temperature range of –55°C to 135°C
using a thermistor with a β value of 3490K such as the
Vishay NTCS0402E3103FLT or NTHS0402N02N1002JE.
See Figure 9.
Table Default Lead-Acid Temperature Compensation
PARAMETER:
REGISTERS THAT DETERMINE 25°C
VALUE:
DEFAULT
VALUE AT
25°C (VOLTS/
CELL)
V_EQUALIZE
VCHARGE_SETTING+VEQUALIZE_DELTA
2.6
V_ABSORB
VCHARGE_SETTING+VABSORB_DELTA
2.4
V_CHARGE
VCHARGE_SETTING
2.2
Coulomb Counter
The LTC4015 features an integrated Coulomb counter
for battery state of charge monitoring. Charge is the time
integral of current. The Coulomb counter is disabled
by default, and can be enabled only via the I²C port
(en_qcount).
There are several I²C accessible registers associated with
the Coulomb counter. The LO and HI alerts listed below
can be disabled. See register map and detailed register
descriptions for details.
en_qcount
1-Bit Enable Coulomb Counter (0x14, Bit 2)
en_qcount_lo_alert 1-Bit Enable Coulomb Counter Low Alert.
(0xOD Bit 13)
en_qcount_hi_alert 1-Bit Enable Coulomb Counter High Alert.
(0xOD Bit 12)
QCOUNT
16-Bits Coulomb Counter Accumulator Value
(0x13)
QCOUNT_LO_
ALERT_LIMIT
16-Bits Coulomb Counter Accumulator Low Alert
Limit. (0x10)
QCOUNT_HI_
ALERT_LIMIT
16-Bits Coulomb Counter Accumulator High Alert
Limit. (0x11)
QCOUNT_
16-Bits Coulomb Counter Prescale Factor. (0x12)
PRESCALE_FACTOR
4015f
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