Datasheet

MAX8662/MAX8663
Power-Management ICs for
Single-Cell, Li+ Battery-Operated Devices
26 ______________________________________________________________________________________
Connect CT to GND to disable the prequalification and
fast-charge timers, allowing the battery to charge indef-
initely in top-off mode, or if other system timers are to
be used to control charging.
Charge-Enable Input (CEN)
Driving CEN high disables the battery charger. Driving
CEN low enables the charger when a valid source is
connected at DC. CEN does not affect the input limit
current, except that driving CEN high and PEN2 low
activates USB suspend mode.
In many systems, there is no need for the system con-
troller (typically a microprocessor) to disable the charg-
er because the SPS circuitry independently manages
charging and adapter/battery power hand-off. In these
situations, CEN can be connected to ground.
Charge Status Output (CHG)
CHG is an open-drain output that indicates charger sta-
tus. CHG is low when the battery charger is in prequali-
fication or fast-charge mode. It is high impedance
when the charger is done, in top-off, or disabled.
The charger faults if the charging timer expires in pre-
qualification or fast charge. In this state, CHG pulses at
1Hz to indicate that a fault occurred.
Battery Charger Thermistor Input (THM)
Battery or ambient temperature can be monitored with
a negative temperature coefficient (NTC) thermistor.
Charging is allowed when the thermistor temperature is
within the allowable range.
The charger enters a temperature suspend state when
the thermistor resistance falls below 3.97k (too hot) or
rises above 28.7k (too cold). This corresponds to a 0
to +50°C range when using a 10k NTC thermistor with
a beta of 3500. The relation of thermistor resistance to
temperature is defined by the following equation:
where:
R
T =
The resistance in ohms of the thermistor at tem-
perature T in Celsius
R25
=
The resistance in ohms of the thermistor at +25°C
ß = The material constant of the thermistor, which typi-
cally ranges from 3000K to 5000K
T = The temperature of the thermistor in °C
Table 2 shows temperature limits for different thermistor
material constants.
Some designs may prefer other trip temperatures. This
can usually be accommodated by connecting a resistor
in series and/or in parallel with the thermistor and/or
using a thermistor with different ß. For example, a
+45°C hot threshold and 0°C cold threshold can be
realized by using a thermistor with a ß of 4250 and con-
necting 120k in parallel. Since the thermistor resis-
tance near 0°C is much higher than it is near +50°C, a
large parallel resistance lowers the cold threshold,
while only slightly lowering the hot threshold.
Conversely, a small series resistance raises the cold
threshold, while only slightly raising the hot threshold.
The charger timer pauses when the thermistor resis-
tance goes out of range: charging stops and the timer
counters hold their state. When the temperature comes
back into range, charging resumes and the counters
continue from where they left off. Connecting THM to
GND disables the thermistor function.
RR e
T
T
+
25
1
273
1
298
β
THERMISTOR ß (K) 3000 (K) 3250 (K) 3500 (K) 3750 (K) 4250 (K)
Resistance at +25°C (k) 1010101010
Resistance at +50°C (k) 4.59 4.30 4.03 3.78 3316
Resistance at 0°C (k) 25.14 27.15 29.32 31.66 36.91
Nominal Hot Trip Temperature (°C) 55 53 50 49 46
Nominal Cold Trip Temperature (°C) -3 -1 0 2 4.5
Table 2. Fault Temperatures for Different Thermistors