LT8490 datasheet(18/48 Pages) AD

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LTC4162-S

Rev B

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OPERATION

Input Overvoltage Protection

The LTC4162 has over-voltage detection on its input. If

VINexceedsapproximately38.6Vasindicatedbyvin_ovlo,

the switching charger will stop delivering power. The

charger will resume switching if VIN falls below roughly

37.2V. The overvoltage detection cutoff circuit provides

only modest over voltage protection and is not intended

to prevent damage in all circumstances.

Measurement Subsystem

TheLTC4162includesa16-bitΔΣA/Dconverterandsignal

multiplexer to monitor numerous analog parameters. It

can measure the voltages at vin, vbat and vout, the input

current (voltage between CLP and CLN), iin, the battery

charge current (voltage between CSP and CSN), ibat, the

batterypackthermistor_voltage,itsowninternaldie_temp

and, once a charge cycle begins, the series resistance of

the battery, bsr. To save battery current, the measure-

ment system is disabled if the battery is the only source

of power (vin_gt_vbat = 0). This can be overridden with

force_telemetry_on. The A/D converter is automatically

multiplexed between all of the measured channels and

its 16-bit signed two's complement results are stored in

registers accessible via the I2C port. The seven channels

measured by the ADC each take approximately 1.6ms to

convert. The maximum range of the 16 bit ΔΣ A/D con-

verter is ±1.8V and it has an internal span term of 18191

counts per Volt. It measures each of the above parameters

through different paths giving different sensitivity terms

for each measurement as summarized in Table 1.

Battery Voltage Measurement

Battery voltage is measured through a resistive voltage

divider whose attenuation ratio is based on the CELLS0/

CELLS1pins.Theresultisreportedinvbat.Thedividerratio

is BATSENS+/7 for each multiple of 6V set by the CELLS0/

CELLS1 pins. The A/D span term is then N • 7/18191 or

N • 384.8µV/LSB where N is 1, 2, 3 or 4 representing a

6V, 12V, 18V or 24V battery respectively. An alert may

be set on battery voltage by setting the vbat based value

vbat_lo_alert_limit or vbat_hi_alert_limit and setting

en_vbat_lo_alert or en_vbat_hi_alert. These alerts are

indicated by vbat_lo_alert or vbat_hi_alert and are cleared

by writing them to 0.

Input Voltage Measurement

Input voltage is measured through a 30:1 resistive volt-

age divider making the A/D span term for input voltage

measurements 30/18191 or 1.649mV/LSB and is digitized

to vin. An alert may be set on input voltage by setting the

value vin_lo_alert_limit or vin_hi_alert_limit and setting

en_vin_lo_alert or en_vin_hi_alert. These alerts are indi-

cated by vin_lo_alert and vin_hi_alert and are cleared by

writing them to 0.

Table 1. Measurement Subsystem LSB Sizes

MEASUREMENT

UNITS

LSB SIZE

OFFSET

BATTERY VOLTAGE

vbat

384.8µV • N*

INPUT VOLTAGE

vin

1.649mV

OUTPUT VOLTAGE

vout

1.653mV

INPUT CURRENT

iin

1.466µV/RSNSI

BATTERY CURRENT

ibat

1.466µV/RSNSB

DIE TEMPERATURE

°C

die_temp

0.0215°C

264.4°C

BATTERY IMPEDANCE

bsr

RSNSB • N/250*

THERMISTOR VOLTAGE

thermistor_voltage

45.833µV/V

*N is 1 for a 6V battery, 2 for a 12V battery, 3 for an 18V battery and 4 for a 24V battery.

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