MAX1645 Datasheet, PDF (26/32 Pages) Maxim Integrated Products – Advanced Chemistry-Independent, Level 2 Battery Chargers with Input Current Limiting

Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
MOSFET Drivers
The low-side driver output DLO swings from 0V to DLOV.
DLOV is usually connected through a filter to LDO. The
high-side driver output DHI is bootstrapped off LX and
swings from V_LX to V_BST. When the low-side driver turns
on, BST rises to one diode voltage below DLOV.
Filter DLOV with an RC circuit whose cutoff frequency
is about 50kHz. The configuration in Figure 1 intro-
duces a cutoff frequency of around 48kHz.
f = 1 / 2πRC = 1 / (2 · π · 33Ω · 0.1µF) = 48kHz
Thermistor Comparators
Four thermistor comparators evaluate the voltage at the
THM input to determine the battery temperature. This
input is meant to be used with the internal thermistor
connected to ground inside the battery pack. Connect
the output of the battery thermistor to THM. Connect a
resistor from THM to V_DD. The resistor-divider sets the
voltage at THM. When the charger is not powered up,
the battery temperature can still be determined if V_DD is
powered from an external voltage source.
Thermistor Bits
Figure 9 shows the expected electrical behavior of a
103ETB-type thermistor (nominally 10kΩ at +25°C ±5%
or better) to be used with the MAX1645/MAX1645A:
• THERMISTOR_OR bit is set when the thermistor
value is >100kΩ. This indicates that the thermistor is
open or a battery is not present. The charger is set to
POR, and the BATTERY_PRESENT bit is cleared.
• THERMISTOR_COLD bit is set when the thermistor
value is >30kΩ. The thermistor indicates a cold bat-
tery. This bit does not affect the charge.
Table 7. Thermistor Bit Settings
1000
100
10
1
0.1
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110
TEMPERATURE (°C)
Figure 9. Typical Thermistor Characteristics
• THERMISTOR_HOT bit is set when the thermistor
value is <3kΩ. This is a latched bit and is cleared by
removing the battery or sending a POR with the
ChargerMode() command. The MAX1645 charger is
stopped unless the HOT_STOP bit is cleared in the
ChargerMode() command. The MAX1645A charger
is stopped unless the HOT_STOP bit is cleared in the
ChargerMode() command or the RES_UR bit is set.
See Table 7.
• THERMISTOR_UR bit is set when the thermistor
value is <500Ω (i.e., THM is grounded).
Multiple bits may be set depending on the value of the
thermistor (e.g., a thermistor that is 450Ω will cause both
the THERMISTOR_HOT and the THERMISTOR_UR bits
to be set). The thermistor may be replaced by fixed-
value resistors in battery packs that do not require the
thermistor as a secondary fail-safe indicator. In this
THERMISTOR
STATUS BIT
DESCRIPTION
WAKE-UP CHARGE
CONTROLLED
CHARGE
REG_UR and RES_HOT
RES_UR and RES_HOT
RES_HOT
(None)
RES_COLD
RES_OR and RES_COLD
Under Range
Under Range
Hot
Normal
Cold
Over Range
Not allowed by MAX1645
Allowed for Timeout
Period by MAX1645A
Not Allowed
Allowed for Timeout
Period
Allowed for Timeout
Period
Float Charge*
Not allowed by MAX1645
Allowed by MAX1645A
Not Allowed
Allowed
Allowed
Not Allowed
*See Battery Present item under Operating Conditions for more information.
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