MCP73853IMF MICROCHIP [Microchip Technology], MCP73853IMF Datasheet - Page 13

• Manufacturer Part Number: MCP73853IMF
• Description: USB Compatible Li-Ion/Li-Polymer Charge Management Controllers
• Manufacturer: MICROCHIP [Microchip Technology]

5.0
5.1
5.1.1
The V
devices. The MCP7385X devices automatically enter a
power-down mode if the voltage on the V
below the UVLO voltage (V
draining the battery pack when the V
present.
5.1.2
Fast charge current regulation can be scaled by placing
a programming resistor (R
to V
maximum fast charge current of 400 mA, typically. The
minimum fast charge current is 85 mA (Typ) and is set
by letting the PROG input float. Equation 5-1 calculates
the value for R
EQUATION 5-1:
The preconditioning trickle charge current and the
charge termination current are scaled to approximately
10% and 7% of I
5.1.3
A 2.55V voltage reference is provided to bias an exter-
nal thermistor for continuous cell temperature monitor-
ing and prequalification. A ratio-metric window
comparison is performed at threshold levels of
V
5.1.4
The MCP73853 continuously monitors temperature by
comparing the voltage between the THERM input and
V
A negative or positive temperature coefficient, NTC or
PTC thermistor and an external voltage divider typically
develops 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.
 2004 Microchip Technology Inc.
Where:
THREF
SS
SS
with the upper and lower temperature thresholds.
I
amps
R
DD
. Connecting the PROG input to V
REG
PROG
/2 and V
DETAILED DESCRIPTION
Analog Circuitry
input is the input supply to the MCP7385X
is the desired fast charge current in
BATTERY MANAGEMENT INPUT
SUPPLY (V
PROG INPUT
CELL TEMPERATURE SENSOR
BIAS (THREF)
CELL TEMPERATURE SENSOR
INPUT (THERM)
R
is in kilo-ohms.
PROG
PROG
THREF
REG
DD
.
, respectively.
=
). The temperature-sensing circuit
/4.
13.32 33.3 I
----------------------------------------------- -
14.1 I
DD1
PROG
STOP
–
, V
REG
). This feature prevents
) from the PROG input
DD2
–
)
DD
1.2
REG
DD
SS
is not applied,
supply is not
DD
allows for a
input falls
Figure 6-1 depicts a typical application circuit with
connection of the THERM input. The resistor values of
R
equations.
For NTC thermistors:
For PTC thermistors:
Applying a voltage equal to V
input disables temperature monitoring.
5.1.5
The TIMER input programs the period of the safety tim-
ers by placing a timing capacitor (C
TIMER input pin and V
programmed via the timing capacitor.
The preconditioning safety timer period:
The fast charge safety timer period:
And, the elapsed time termination period:
The preconditioning timer starts after qualification and
resets when the charge cycle transitions to the
constant-current, fast charge phase. The fast charge
timer and the elapsed timer start after the MCP7385X
devices transition 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.
During thermal regulation, the timer is slowed down
proportional to the charge current.
Where:
T1
and R
R
resistance values at the temperature window
of interest.
COLD
t
PRECON
t
TIMER SET INPUT (TIMER)
t
TERM
FAST
T2
R
R
T1
T2
R
R
and
T1
T2
are calculated with the following
=
=
=
=
MCP73853/55
=
=
=
2 R
----------------------------------------------
2 R
----------------------------------------------
R
C
------------------ -
C
------------------ -
R
0.1 F
0.1 F
COLD
2 R
----------------------------------------------
2 R
----------------------------------------------
R
R
C
------------------ -
TIMER
TIMER
0.1 F
HOT
HOT
COLD
R
TIMER
HOT
SS
COLD
COLD
COLD
COLD
–
. Three safety timers are
–
3 R
–
–
3 R
are
1.5Hours
3.0Hours
THREF
R
R
1.0Hours
HOT
COLD
R
R
HOT
HOT
HOT
R
R
COLD
TIMER
the
HOT
HOT
DS21915A-page 13
/3 to the THERM
) between the
thermistor