MAX1645B Datasheet, PDF (28/32 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
NOTE: SB 1 POWERING SYSTEM
SB 2 CHARGING
SMART BATTERY 1
SMART BATTERY 2
AC
AC-DC
CONVERTER
(UNREGULATED)
SYSTEM HOST
(SMBus HOST)
SMART BATTERY
SELECTOR
SMBus
SAFETY SIGNAL
V_CHARGE
MAX1645B
SMART
BATTERY
CHARGER
CRITICAL EVENTS
BATTERY DATA/STATUS REQUESTS
SMBus
Figure 11. Typical System Using Multiple Smart Batteries
Table 8. Smart Battery Charger Type
by SMBus Mode and Charge Algorithm
Source
SMBus MODE
Slave only
Slave/master
CHARGE ALGORITHM SOURCE
BATTERY
MODIFIED FROM
BATTERY
Level 2
Level 3
Level 3
Level 3
Note: Level 1 smart battery chargers were defined in the ver-
sion 0.95a specification. While they can correctly interpret
smart battery end-of-charge messages, minimizing over-
charge, they do not provide truly chemistry-independent
charging. They are no longer defined by the Smart Battery
Charger Specification and are explicitly not compliant with this
and subsequent smart battery charger specifications.
sumption of the Schottky diode. To minimize power loss,
select a MOSFET with an R_DS(ON) of 50mΩ or less. This
MOSFET must be able to deliver the maximum current
as set by R1. D1 and P1 provide protection from
reversed voltage at the adapter input.
N-channel MOSFETs N1 and N2 are the switching
devices for the buck controller. High-side switch N1
should have a current rating of at least 6A and have an
R_DS(ON) of 50mΩ or less. The driver for N1 is powered
by BST; its current should be less than 10mA. Select a
MOSFET with a low total gate charge and determine the
required drive current by I_GATE = Q_GATE ✕ f (where f is
the DC-to-DC converter maximum switching frequency
of 400kHz).
The low-side switch N2 should also have a current rating
of at least 3A, have an R_DS(ON) of 100mΩ or less, and a
total gate charge less than 10nC. N2 is used to provide
the starting charge to the BST capacitor C14. During nor-
mal operation, the current is carried by Schottky diode
D2. Choose a 3A or higher Schottky diode.
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