LTC1760 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1760' PDF : 44 Pages View PDF
LTC1760
APPLICATIONS INFORMATION
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)
400
3.3k
400
Thermistor Range
OVER_RANGE
IDEAL_RANGE
UNDER_RANGE
ISAFETYX (μA)
1.05
42.2
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:
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)
400
Thermistor Range
UNDER_RANGE
ISAFETYX (μA)
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
1760fa
39
Share Link: 
