MAX1645B Datasheet, PDF (26/32 Pages) Maxim Integrated Products – Advanced Chemistry-Independent, Level 2 Battery Charger with Input Current Limiting

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Load and Source Switch Drivers
The MAX1645B can drive two P-channel MOSFETs to
eliminate voltage drops across the Schottky diodes,
which are normally used to switch the load current from
the battery to the main DC source:
• The source switch P1 is controlled by PDS. This P-
channel MOSFET is turned on when CVS rises to
300mV above BATT and turns off when CVS falls to
100mV above BATT. The same signal that controls
the PDS also sets the POWER_FAIL bit in the
Charger Status() register. See Operating Conditions.
• Load switch P2 is controlled by PDL. This P-channel
MOSFET is turned off when the CVS rises to 100mV
below BATT and turns on when CVS falls to 300mV
below BATT.
Dropout Operation
The MAX1645B has a 99.99% duty-cycle capability
with a 10ms maximum on-time and 1µs off-time. This
allows the charger to achieve dropout performance lim-
ited only by resistive losses in the DC-DC converter
components (P1, R1, N1, R2; see Figure 1). The actual
dropout voltage is limited to 300mV between CVS and
BATT by the power-fail comparator (see Operating
Conditions).
Applications Information
Smart Battery Charging
System/Background Information
A smart battery charging system, at a minimum, con-
sists of a smart battery and smart battery charger com-
patible with the Smart Battery System Specifications
using the SMBus.
A system can use one or more smart batteries. Figure 10
shows a single-battery system. This configuration is
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
typically found in notebook computers, video cameras,
cellular phones, or other portable electronic equipment.
Another configuration uses two or more smart batteries
(Figure 11). The smart battery selector is used either to
connect batteries to the smart battery charger or the
system, or to disconnect them, as appropriate. For
each battery, three connections must be made: power
(the battery’s positive and negative terminals), the
SMBus (clock and data), and the safety signal (resis-
tance, typically temperature dependent). Additionally,
the system host must be able to query any battery so it
can display the state of all batteries present in the system.
Figure 11 shows a two-battery system where battery 2 is
being charged while battery 1 is powering the system.
This configuration can be used to “condition” battery 1,
allowing it to be fully discharged prior to recharge.
Table 7. Thermistor Bit Settings
THERMISTOR
STATUS BIT
RES_UR and RES_HOT
RES_HOT
(None)
RES_COLD
RES_OR and RES_COLD
DESCRIPTION
Underrange
Hot
Normal
Cold
Overrange
WAKE-UP CHARGE
Allowed for timeout period
Not allowed
Allowed for timeout period
Allowed for timeout
period
Float charge*
*See Battery Present in the Operating Conditions section for more information.
CONTROLLED
CHARGE
Allowed
Not allowed
Allowed
Allowed
Not allowed
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