MCP73864-I/SL Ver la hoja de datos (PDF) - Microchip Technology
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MCP73864-I/SL
Microchip Technology
MCP73864-I/SL Datasheet PDF : 34 Pages
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5.0 DETAILED DESCRIPTION
5.1 Analog Circuitry
5.1.1 BATTERY MANAGEMENT INPUT
SUPPLY (VDD1, VDD2)
The VDD input is the input supply to the MCP7386X.
The MCP7386X automatically enters a Power-down
mode if the voltage on the VDD input falls below the
UVLO voltage (VSTOP). This feature prevents draining
the battery pack when the VDD supply is not present.
The VDD inputs should be tied to ground with a resistor
<= 1.5 kΩ to prevent VDD from floating and staying at
VBAT level if the input supply is disconnected. The
resistor will assure that VDD < VBAT when the input
supply is removed.
5.1.2 PROG INPUT
Fast charge current regulation can be scaled by placing
a programming resistor (RPROG) from the PROG input
to VSS. Connecting the PROG input to VSS allows for a
maximum fast charge current of 1.2A, typically. The
minimum fast charge current is 100 mA, set by letting
the PROG input float. The following formula calculates
the value for RPROG:
Where:
RPROG = -1-1-3--2-.--2-----–-I---R1---E1---G-----–-I---R1---E.--2-G--
IREG = the desired fast charge current in amps.
RPROG = measured in kΩ
The preconditioning trickle-charge current and the
charge termination current are scaled to approximately
10% and 8% of IREG, respectively.
5.1.3
CELL TEMPERATURE SENSOR
BIAS (THREF)
A 2.5V voltage reference is provided to bias an external
thermistor for continuous cell temperature monitoring
and prequalification. A ratio metric window comparison
is performed at threshold levels of VTHREF/2 and
VTHREF/4.
5.1.4
CELL TEMPERATURE SENSOR
INPUT (THERM)
The MCP73861/2/3/4 continuously monitors tempera-
ture by comparing the voltage between the THERM
input and VSS with the upper and lower temperature
thresholds. A negative or positive temperature coeffi-
cient, NTC or PTC thermistor and an external voltage-
divider typically develop this voltage. The temperature
sensing circuit has its own reference to which it
performs a ratio metric comparison. Therefore, it is
immune to fluctuations in the supply input (VDD). The
2004-2013 Microchip Technology Inc.
MCP73861/2/3/4
temperature-sensing circuit is removed from the
system when VDD is not applied, eliminating additional
discharge of the battery pack.
Figure 6-1 depicts a typical application circuit with
connection of the THERM input. The resistor values of
RT1 and RT2 are calculated with the following
equations.
For NTC thermistors:
RT1 = -2----R----C-R---O-C--L-O--D--L---D–-----R----H-R--O--H--T-O----T-
RT2 = 2-R----C---O--R--L--C-D--O---–-L---D3---------R-R---H-H---OO----TT-
For PTC thermistors:
RT1 = 2-----R----H-R---O-C---TO----–L---D-R----C----O-R--L-H--D--O----T-
RT2 = 2-R----H---O--R--T--C--–-O----3L---D------R----RC---OH----LO---D-T-
Where:
RCOLD and RHOT are the thermistor resis-
tance values at the temperature window of
interest.
Applying a voltage equal to VTHREF/3 to the THERM
input disables temperature monitoring.
5.1.5 TIMER SET INPUT (TIMER)
The TIMER input programs the period of the safety
timers by placing a timing capacitor (CTIMER) between
the TIMER input pin and VSS. Three safety timers are
programmed via the timing capacitor.
The preconditioning safety timer period:
tPRECON = C---0--T-.-1-I--M----EF---R- 1.0Hours
The fast charge safety timer period:
tFAST = -C--0--T.--1-I-M-----EF---R- 1.5Hours
The elapsed time termination period:
tTERM = C---0--T-.-1-I--M----EF---R- 3.0Hours
The preconditioning timer starts after qualification and
resets when the charge cycle transitions to the fast
charge, Constant-current mode. The fast charge timer
and the elapsed timer start once the MCP7386X
transitions from preconditioning. The fast charge timer
resets when the charge cycle transitions to the
Constant-voltage mode. The elapsed timer will expire
and terminate the charge if the sensed current does not
diminish below the termination threshold.
DS21893F-page 17
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