LTC4015 datasheet(20/76 Pages) LINER

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LTC4015

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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 ENABLE

BITS (0x0E)

ALERT

REPORTING

BITS (0x37)

Equalize

Absorb

Charger Suspended

Precharge

CC_CV

NTC Pause

Timer Termination

C/x Termination

Max Charge Time Fault

Battery Missing Fault

Battery Short Fault

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

ENABLE BITS

(0x0F)

ALERT

REPORTING

BITS (0x38)

UVCL (VIN Undervoltage Charge Current

Limiting)

ICL (IIN Charge Current Limiting)

CC (Constant-Current Mode)

CV (Constant-Voltage Mode)

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 VIN,

SYS and BATSENS, the current into the SYS node (voltage

across RSNSI), the battery charge current (voltage across

RSNSB), the voltage across the battery pack thermistor,

and its own internal die temperature. After a charge

cycle begins the LTC4015 uses the appropriate analog

parameterstocalculatetheseriesresistanceofthebattery.

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) =

54.932479

µV

MEASUREMENT

SYMBOL

NUMBER

LSB SCALING

LSB SIZE

UNITS

VBATSENS/Cellcount (Lithium Chemistries)

VBAT

0x3A

*7/2

192.264

µV

VBATSENS/Cellcount (Lead-Acid)

VBAT

0x3A

*7/3

128.176

µV

VIN

0x3B

*30

1.648

VSYS

0x3C

*30

1.648

VRSNSB (VCSP – VCSN)

IBAT

0x3D

/37.5

1.465

µV

VRSNSI (VCLP – VCLN)

IIN

0x3E

/37.5

1.465

µV

Die Temperature (Note 1)

DIE_TEMP

0x3F

54.932

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.

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