MAX1782ETM+T Maxim Integrated, MAX1782ETM+T Datasheet - Page 6

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MAX1782ETM+T

Manufacturer Part Number
MAX1782ETM+T
Description
Battery Management Adv Smart Battery Pack Controller
Manufacturer
Maxim Integrated
Series
MAX1782r
Datasheet
Once the switch turns off, it remains off for at least the
minimum off-time. After the minimum off-time, the P-
channel MOSFET turns on if the cell voltage is lower
than the BATT regulation voltage. A C
0.33µF sets a minimum off-time of 33ms.
At the beginning of the pulsed top-off state, charge cur-
rent is modulated at approximately an 83% duty cycle.
Toward the end of top-off, charge current stays off for
long periods of time between single “on” pulses. During
these final pulses, the instantaneous cell voltage may
exceed the BATT regulation voltage by several hun-
dred millivolts, but these pulses are orders of magni-
tude shorter than the electrochemical time constant of
the Li+ cell and do no harm. Pulsed top-off charge
ends when the cell voltage no longer falls below the
BATT regulation voltage. Figure 2 shows the state
machine.
One reason the MAX1736 Li+ charger is so compact
and simple is that the charging current is set by the
SOT23, Single-Cell Li+ Battery Charger
for Current-Limited Supply
6
Figure 1. Functional Diagram
____________________________________________________________________________________________________
Selecting External Components
CT
10µA
2µA
V
BATT
+ 100mV
350k
Input Power Supply
1.4V
0.4V
EN
IN
CT
value of
IN
MACHINE
GND
STATE
external power source, not by the MAX1736. The P-
channel MOSFET in Figure 3’s application circuit is
either on or off, allowing the source to be directly con-
nected to the cell or disconnected. Therefore, it is
important to choose a power supply with the correct
current limit for the cell to be charged. In most applica-
tions, this will be a small wall cube with an open-circuit
output voltage of 5V to 12V, which is specified as “cur-
rent limited” or “constant current.”
Some low-cost wall cubes may have poor transient
characteristics. For these wall cubes, output current
may exceed the specified current limit by several times
when the load is quickly connected. The MAX1736 lim-
its this current peak by controlling the slew rate of the
P-channel MOSFET. See C
information.
The P-channel MOSFET switches the current-limited
source on and off. Because of the intentionally slow
switching times and limited slew rate, the MAX1736 is
not particular about the power FET it drives. Spec-
ifications to consider when choosing an appropriate
GATE
REF
IN
6mA
(MAX1736EUT41)
MAX1736EUT42
4.2V (4.1V)
5V
CT
BATT
and C
PMOS Switch
GATE
for more

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