ltc1760 Linear Technology Corporation, ltc1760 Datasheet - Page 13

• Manufacturer Part Number: ltc1760
• Description: Dual Smart Battery System Manager
• Manufacturer: Linear Technology Corporation

1 Overview
The LTC1760 is composed of an SMBus interface with
dual port capability, a sequencer for managing system
power and the charging and discharging of two batteries,
a battery charger controller, charge mux controller, power-
path controller, a 10-bit current DAC (I
voltage DAC (V
software for generating composite battery information, it
forms a complete Smart Battery System Manager for
charging and selecting two smart batteries. The battery
charger is controlled by the sequencer which uses the
level 3 SMBus interface to read ChargingVoltage(), Volt-
age(), ChargingCurrent(), Current(), Alarm() and
BatteryMode(). This information, together with thermistor
measurements allows the sequencer to select the charg-
ing battery and safely servo on voltage and current.
Charging can be accomplished only if the voltage at DCDIV
indicates that sufficient voltage is available from the input
power source, usually an AC adapter. The charge mux,
which selects the battery to be charged, is capable of
charging both batteries simultaneously. The charge mux
switch drivers are configured to allow charger current to
share between the two batteries and to prevent current
from flowing in a reverse direction in the switch. The
amount of current that each battery receives will depend
upon the relative capacity of each battery and the battery
voltage. This can result in significantly shorter charging
times (up to 50% for Li-Ion batteries) than sequential
charging of each battery.
The sequencer also selects which of the pairs of PFET
switches will provide power to the system load. If the
system voltage drops below the threshold set by the
LOPWR resistor divider, then all of the output-side PFETs
are turned on quickly. The input-side PFETs act as diodes
in this mode and power is taken from the highest voltage
source available at the DCIN, BAT1, or BAT2 inputs. The
input-side powerpath switch driver that is delivering power
then closes its input switch to reduce the power dissipa-
tion in the PFET bulk diode. In effect, this system provides
OPERATIO
DAC
U
). When coupled with optional system
(Refer to Block Diagram and Typical Application Figure)
DAC
) and 11-bit
diode-like behavior from the FET switches, without the
attendant high power dissipation from diodes. The HOST
is informed of this 3-Diode mode status when it polls the
powerpath status register via the SMBus interface. High
speed powerpath switching at the LOPWR trip point is
handled autonomously.
Simultaneous discharge of both batteries is supported.
The switch drivers prevent reverse current flow in the
switches and automatically discharge both batteries into
the load, sharing current according to the relative capacity
of the batteries. Simultaneous dual discharge can increase
battery operating time by up to 10% by reducing losses in
the switches and reducing internal battery losses associ-
ated with high discharge rates.
2 The SMBus Interface
2.1 SMBus Interface Overview
The SMBus interface allows the LTC1760 to communicate
with two batteries and the SMBus Host. The SMBus
Interface supports true dual port operation by allowing the
SMBus Host to be connected to the SMBus of either
battery. The LTC1760 is able to operate as an SMBus
master or slave device.
References:
Smart Battery System Manager Specification: Revision
1.1, SBS Implementers Forum.
Smart Battery Data Specification: Revision 1.1, SBS
Implementers Forum.
Smart Battery Charger Specification: Revision 1.1, SBS
Implementers Forum
System Management Bus Specification: Revision 1.1,
SBS Implementers Forum
I
2
C-Bus and How to Use it: V1.0, Philips Semiconductor.
LTC1760
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