MCP73844 Microchip Technology, MCP73844 Datasheet - Page 13

• Manufacturer Part Number: MCP73844
• Description: (MCP73841 - MCP73844) Advanced Single or Dual Cell Lithium-Ion/ Lithium-Polymer Charge Management Controllers
• Manufacturer: Microchip Technology

5.0
5.1
5.1.1
Fast charge current regulation is maintained by the
voltage drop developed across an external sense
resistor (R
following formula calculates the value for R
The preconditioning trickle-charge current and the
charge termination current are scaled to approximately
10% and 7% of I
5.1.2
The V
The MCP7384X automatically enters a power-down
mode if the voltage on the V
undervoltage lockout voltage (V
prevents draining the battery pack when the V
supply is not present.
5.1.3
A 2.55V voltage reference is provided to bias an
external thermistor for continuous cell temperature
monitoring and pre-qualification. A ratio metric window
comparison is performed at threshold levels of
V
is provided by both the MCP73841 and MCP73842.
5.1.4
The MCP73841 and MCP73842 continuously monitor
temperature by comparing the voltage between the
THERM input and V
temperature thresholds. A negative or positive
temperature coefficient (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 (V
is removed from the system when V
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
R
equations.
THREF
T1
2004 Microchip Technology Inc.
where:
I
REG
and R
DD
/2 and V
DETAILED DESCRIPTION
Analog Circuitry
is the desired fast charge current in amps
input is the input supply to the MCP7384X.
SENSE
CHARGE CURRENT SENSE INPUT
(SENSE)
BATTERY MANAGEMENT INPUT
SUPPLY (V
CELL TEMPERATURE SENSOR
BIAS (THREF)
CELL TEMPERATURE SENSOR
INPUT (THERM)
T2
THREF
) applied to the SENSE input pin. The
REG
are calculated with the following
R
DD
SENSE
, respectively.
). The temperature-sensing circuit
/4. Cell temperature monitoring
SS
DD
=
with the upper and lower
)
V
------------
I
REG
FCS
DD
input falls below the
STOP
DD
). This feature
is not applied,
SENSE
:
DD
For NTC thermistors:
For PTC thermistors:
Applying a voltage equal to 0.85V to the THERM input
disables temperature monitoring.
5.1.5
The TIMER input programs the period of the safety
timers by placing a timing capacitor (C
the TIMER input pin and V
programmed via the timing capacitor.
The preconditioning safety timer period:
The fast charge safety timer period:
The elapsed time termination period:
The preconditioning timer starts after qualification and
resets when the charge cycle transitions to the con-
stant-current, fast charge phase. The fast charge and
elapsed timers start once the MCP7384X transitions
from preconditioning. The fast charge timer resets
when the charge cycle transitions to the constant-volt-
age phase. The elapsed timer will expire and terminate
the charge if the sensed current does not diminish
below the termination threshold.
where:
R
values at the temperature window of interest.
COLD
t
and R
PRE CON
t
t
TIMER SET INPUT (TIMER)
TERM
FAST
MCP73841/2/3/4
R
R
R
R
T1
T2
T1
T2
HOT
=
=
=
=
=
=
=
2
----------------------------------------------
2
----------------------------------------------
R
2
----------------------------------------------
2
----------------------------------------------
R
C
------------------ -
C
------------------ -
0.1 F
are the thermistor resistance
0.1 F
COLD
H OT
R
R
C
------------------ -
TIMER
TIMER
0.1 F
COLD
H OT
TIMER
R
R
R
R
COLD
COLD
COLD
COLD
–
SS
–
–
3
3
–
R
. Three safety timers are
1.5Hours
3.0Hours
R
CO LD
R
1.0Hours
H OT
R
R
R
R
R
CO LD
H OT
H OT
H OT
H OT
H OT
DS21823B-page 13
TIMER
) between