MAX1645B Datasheet, PDF (27/32 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
V_CC
+12V, -12V
SYSTEM
POWER
SUPPLY
DC (UNREGULATED) / V_BATTERY
SYSTEM
POWER
CONTROL
AC
SYSTEM HOST
(SMBus HOST)
V_BATTERY
DC (UNREGULATED)
AC-DC
CONVERTER
(UNREGULATED)
SMART
BATTERY
SAFETY
SIGNAL
MAX1645B
SMART BATTERY
CHARGER
CRITICAL EVENTS
BATTERY DATA/STATUS REQUESTS
CHARGING VOLTAGE/CURRENT
REQUESTS
CRITICAL EVENTS
SMBus
Figure 10. Typical Single Smart Battery System
Smart Battery Charger Types
Two types of smart battery chargers are defined: Level
2 and Level 3. All smart battery chargers communicate
with the smart battery using the SMBus; the two types
differ in their SMBus communication mode and whether
they modify the charging algorithm of the smart battery
(Table 8). Level 3 smart battery chargers are supersets
of Level 2 chargers and, as such, support all Level 2
charger commands.
Level 2 Smart Battery Charger
The Level 2 or smart battery-controlled smart battery
charger interprets the smart battery’s critical warning
messages and operates as an SMBus slave device to
respond to the smart battery’s ChargingVoltage() and
ChargingCurrent() messages. The charger is obliged to
adjust its output characteristics in direct response to
the ChargingVoltage() and ChargingCurrent() mes-
sages it receives from the battery. In Level 2 charging,
the smart battery is completely responsible for initiating
the communication and providing the charging algo-
rithm to the charger.
The smart battery is in the best position to tell the smart
battery charger how it needs to be charged. The charg-
ing algorithm in the battery may request a static charge
condition or may choose to periodically adjust the
smart battery charger’s output to meet its present
needs. A Level 2 smart battery charger is truly chem-
istry independent and, since it is defined as an SMBus
slave device only, the smart battery charger is relatively
inexpensive and easy to implement.
Selecting External Components
Table 9 lists the suppliers’ contacts; Table 10 lists the
recommended components and refers to the circuit of
Figure 1. The following sections describe how to select
these components.
MOSFETs and Schottky Diodes
Schottky diode D1 provides power to the load when the
AC adapter is inserted. Choose a 3A Schottky diode or
higher. This diode may not be necessary if P1 is used.
The P-channel MOSFET P1 turns on when V_CVS >
V_BATT. This eliminates the voltage drop and power con-
______________________________________________________________________________________ 27