LTC4162IUFD-FST#PBF datasheet(21/52 Pages) AD

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LTC4162-F

Rev A

For more information www.analog.com

OPERATION

TheLTC4162thermistormeasurementsystemisdesigned

specifically for a thermistor with a β25/85 value of 3490K

and returns thermistor_voltage where:

thermistor _ voltage = 18191• 1.2 •

RNTC

RNTC+RNTCBIAS

where typically RNTCBIASissetequaltoR25,the25°Cvalue

of the thermistor. To arrive at the thermistor's temperature

in °C from thermistor_voltage substitute RNTC from:

RNTC = RNTCBIAS •

thermistor_ voltage

18191• 1.2 − thermistor_voltage

into Equation 1 or Equation 2.

For thermistors with a β25/85 value higher than 3490K

see Alternate Thermistors and Biasing in the Applications

section.

Output Current Measurement

There is no sense resistor dedicated to measuring output

current but its value can be obtained nonetheless. Output

current is delivered from the input supply if vin_gt_vbat

is true and from the battery if it is false.

If vin_gt_vbat is true and the battery charger is enabled

(en_chg is true) then the input current measurement will

be the sum of current to the switching charger and the

output load. In this instance the switching charger will

need to be disabled with suspend_charger to obtain an

output current reading. It's also possible that the charger

may already be terminated. If en_chg is false then set

telemetry_speed to tel_high_speed, wait 20ms or more,

and record iin as output current. If en_chg is true then set

both suspend_charger and force_telemetry_on to 1 and

telemetry_speed to tel_high_speed, wait 20ms or more

for at least one telemetry cycle, and again record iin as

output current. suspend_charger should then be cleared.

Note that suspending the charger resets the tchargetimer

and tcvtimer termination timers to 0.

On the other hand if vin_gt_vbat is false then the output

currentwillbedeliveredfromthebatteryanditsvaluecanbe

obtainedfrom–ibat.Sincevin_gt_vbatislow,thetelemetry

system will be disabled and the ibat reading will be stale.

To enable the telemetry system, set force_telemetry_on to

1andtelemetry_speedtotel_high_speed.telemetry_valid

indicates when fresh telemetry readings are available. To

avoid polling for telemetry_valid a telemetry_valid_alert

can be set with en_telemetry_valid_alert. Once the read-

ing is obtained, force_telemetry_on can be cleared or

telemetry_speed set to tel_low_speed for power savings.

Low Power Telemetry

Ifinputpowerisavailable(vin_gt_vbat=1),andthebattery

is being charged, the telemetry system will be in its high

speed mode returning results at a rate of roughly once

per 11ms. If, on the other hand, charging has terminated

normally or paused due to battery temperature out of

range, the telemetry system will drop back to a rate of

about once every 5 seconds to save power. When input

power is not available (vin_gt_vbat = 0) it is still possible

to collect telemetry data by setting force_telemetry_on. To

save power in this mode the telemetry system will default

to the lower speed 5 second mode. To force the higher

telemetry rate, and suffer the higher quiescent current

of roughly 2.5mA, the telemetry_speed can be set to the

higher ~11ms rate by setting it to tel_high_speed.

Configurable Limit Alert Subsystem

The I2C port also supports the SMBus SMBALERT pro-

tocol, including the Alert Response Address. An alert can

optionally be generated if a monitored parameter exceeds

a programmed limit or if a selected battery charger_state

or any of a wide number of other charge_status change or

fault events occur. This off-loads much of the continuous

monitoringfromthesystem'smicrocontrollerandontothe

LTC4162; reducing bus traffic and microprocessor load.

The SMBALERT pin is asserted (pulled low) whenever

an enabled alert occurs. After asserting an interrupt, the

LTC4162 responds to the host's Alert Response Address

(ARA = 0b0001100[1]) with its own read address. If an-

other part with a pending alert and a lower address also

responds, that part wins the arbitration and the LTC4162

will stop responding to this ARA, keeping its SMBALERT

pin asserted. Only a response of the LTC4162's complete

read address will clear the LTC4162's SMBALERT signal.

LTC4162IUFD-FST#PBF 数据表(PDF) 21 Page - Analog Devices

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