LTC4015_15 Datasheet, PDF (20/76 Pages) Linear Technology – Multichemistry Buck Battery Charger Controller with Digital Telemetry System

LTC4015
Operation
Table 2. Shows a Summary of LTC4015 Charger State Alerts.
Each Alert Has an Associated Enable (or Mask), and Bit That Is
Set to 1 to Indicate the Alert Has Occurred.
CHARGER STATE ALERTS
ALERT
ALERT ENABLE REPORTING
BITS (0x0E)
BITS (0x37)
Equalize
10
10
Absorb
9
9
Charger Suspended
8
8
Precharge
7
7
CC_CV
6
6
NTC Pause
5
5
Timer Termination
4
4
C/x Termination
3
3
Max Charge Time Fault
2
2
Battery Missing Fault
1
1
Battery Short Fault
0
0
Table 3. Shows a Summary of LTC4015 Charger Status Alerts.
These Alerts Indicate Which Control Loop Is in Control During
Charging. Each Alert Has an Associated Enable (or Mask), and
Bit That Is Set to 1 to Indicate the Alert Has Occurred.
CHARGER STATUS ALERTS
ALERT
ALERT
ENABLE BITS REPORTING
(0x0F)
BITS (0x38)
UVCL (V_IN Undervoltage Charge Current
3
3
Limiting)
ICL (I_IN Charge Current Limiting)
CC (Constant-Current Mode)
2
2
1
1
CV (Constant-Voltage Mode)
0
0
Measurement Subsystem
The LTC4015 includes a 14-bit analog-to-digital converter
(ADC) and signal channel multiplexer to monitor several
analog parameters. It can measure the voltages at V_IN,
SYS and BATSENS, the current into the SYS node (voltage
across R_SNSI), the battery charge current (voltage across
R_SNSB), the voltage across the battery pack thermistor,
and its own internal die temperature. After a charge
cycle begins the LTC4015 uses the appropriate analog
parameters to calculate the series resistance of the battery.
To save battery power the measurement system will not
run if the battery is the only source of power, unless the
force_meas_sys_on bit is set.
The converter is automatically multiplexed between all
of the measured channels and its results are stored in
registers accessible via the I²C port.
The seven channels measured by the ADC each take ap-
proximately 1.6ms to measure. The result of the analog-
to-digital conversion is stored in a 16-bit register as a
signed, two’s complement number. The lower two bits
of this number are sub-bits. These bits are ADC outputs
which are too noisy to be reliably used on any single
conversion, however, they may be included if multiple
samples are averaged. The maximum range of the ADC
is ±1.8V, which gives a LSB size of 3.6V/65535 (2¹⁶ – 1).
Table 4 summarizes the LSB scaling and resultant LSB
size for these ADC measurements.
Table 4. Measurement Subsystem Scaling and LSB Size
ADC LSB (3.6V/65535) =
MEASUREMENT
REGISTER
SYMBOL
V_BATSENS/Cellcount (Lithium Chemistries)
V_BATSENS/Cellcount (Lead-Acid)
V_IN
V_SYS
V_RSNSB (V_CSP – V_CSN)
V_RSNSI (V_CLP – V_CLN)
Die Temperature (Note 1)
VBAT
VBAT
VIN
VSYS
IBAT
IIN
DIE_TEMP
REGISTER
NUMBER
0x3A
0x3A
0x3B
0x3C
0x3D
0x3E
0x3F
LSB SCALING
*7/2
*7/3
*30
*30
/37.5
/37.5
1
54.932479
LSB SIZE
192.264
128.176
1.648
1.648
1.465
1.465
54.932
µV
UNITS
µV
µV
mV
mV
µV
µV
µV
Note 1: DIE_TEMP is the ADC conversion of a internal PTAT (proportional to absolute temperature) voltage. DIE temperature = (DIE_TEMP – 12010)/45.6
in °C.
4015f
20
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