LTC4100 datasheet(39/48 Pages) LINER

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LTC1760

1760fa

For thermistors that are IDEAL-RANGE:

ISAFETYX = 4/64 • VVCC2/(RXB + RTHX) + 2/64 • VVCC2/

(R1A +RTHX)

For thermistors that are HOT-RANGE:

ISAFETYX = 4/64 • VVCC2/(RXB + RTHX) + 4/64 • VVCC2/

(R1A +RTHX)

RTHX is the impedance of the battery’s thermistor to

ground.

RXB = 54.9k

RXA = 1.13k

Sample calculation of ISAFETYX with VVCC2 = 5.2V

Thermistor Impedance

RTHX (W)

Thermistor Range

ISAFETYX (μA)

400

OVER_RANGE

1.05

3.3k

IDEAL_RANGE

42.2

400

UNDER_RANGE

218

IVLIMIT = VVCC2/(RVLIMIT + RLIM_PU).

IILIMIT = VVCC2/(RILIMIT + RLIM_PU).

RLIM_PU is the typical pull-up impedance at VLIMIT

and ILIMIT.

RLIM_PU = 34k.

RVLIMIT is the value of the resistance from VLIMIT to

GND.

RILIMIT is the value of the resistance from ILIMIT to

GND.

ISMB is the current used for communicating with the

SMBus Host and depends on the amount of bus traffic.

ISMB_BATX is the current used for communicating

with Battery1 or Battery2.

ISMB_BATX = 350μA • 0.0155 = 5.425μA.

ISMBALERT is defined in “Electrical Characteristics.”

Sample calculation of IDCIN_CHG with two Li-Ion batteries

(RTHX = 400), RVLIMIT = RILIMIT = 30k, VCC2 = 5.2V, and

no SMBus Host communication:

APPLICATIONS INFORMATION

IDCIN_CHG = ICH1 + IVCC2_AC1 + ISAFETY1 + ISAFETY2 +

IVLIM + IILIM + ISMB + ISMB_BAT1 + ISMB_BAT2 +

ISMBALERT

= 1.3mA + 700μA + 218μA + 218μA +81μA + 81μA

+ 0μA + 5.4μA + 5.4μA + 0μA = 2.62mA

The total operating current through BAT1 and BAT2 when

AC is not present (IBAT_NOAC) is given by:

IBAT_NOAC = IBAT + IVCC2_AC0 + ISAFETY1 + ISAFETY2 +

ISMB + ISMB_BAT1_AC0 + ISMB_BAT2_AC0 + ISMBALERT

where:

IBAT is defined in “Electrical Characteristics.”

IVCC2_AC0 is defined in “Electrical Characteristics.”

ISAFETYX is the current used to test the battery

thermistor connected to SAFETY1 or SAFETY2.

ISAFETYX = 2/64 • VVCC2/(RXB + RTHX).

RTHX is the impedance of the battery’s thermistor to

ground.

RXB = 54.9k.

Sample calculation of ISAFETY with VVCC2 = 5.2V

Thermistor Impedance

RTHX (Ω)

Thermistor Range

ISAFETYX (μA)

400

UNDER_RANGE

2.9

ISMB_BATX_ACO is the current used for communicat-

ing with Battery1 or Battery2 when AC in not present.

ISMB_BATX_AC0 = 350μA • 0.00687 = 2.404μA.

ISMB is the current used for communicating with the

SMBus Host and depends on the amount of bus

traffic.

Sample calculation with two Li-Ion batteries (RTHX =

400), VCC2 = 5.2V, and no SMBus Host communication:

IBAT_NOAC – IBAT + IVCC2_AC0 + ISAFETY1 + ISAFETY2 +

ISMB + ISMB_BAT1_AC0 + ISMB_BAT2_AC0 + ISMBALERT

= 175μA + 80μA + 2.9μA + 2.9μA + 0μA + 2.4μA +

2.4μA + 0μA = 265μA

LTC4100 数据表(PDF) 39 Page - Linear Technology

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