ltc1760 Linear Technology Corporation, ltc1760 Datasheet - Page 27

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

OPERATIO
4 System Power Management Algorithm and Battery
Calibration
4.1 Turning Off System Power
The LTC1760 allows the user to turn off system power
using the LTC(POWER_OFF) bit. When POWER_OFF is
asserted high all power management functions are by-
passed and the LTC1760 will turn off DCIN, BAT2 and
BAT1 power paths. This feature allows the user to power
down the system. Charging is still allowed when
POWER_OFF is asserted high.
4.2 Power-By Algorithm When No Battery is Being
Calibrated
The LTC1760 will always attempt to maintain system
power. The preferred configuration is to remain in 3- Diode
mode. In 3-Diode mode, power will be provided by BAT1,
BAT2 and DCIN with the source at the highest voltage
potential automatically providing all the power. Sources at
similar voltage potentials will share power based on their
capacity.
The following conditions will cause the LTC1760 to modify
its preferred power-by algorithm.
1. A battery issues a terminate discharge alarm and
AC_PRESENT is high. The LTC1760 will select the other
battery and DCIN to power the system.
2. A battery issues a terminate discharge alarm and
AC_PRESENT is low. The LTC1760 will select the other
battery to power the system.
3. A battery issues a terminate discharge alarm,
AC_PRESENT is low, and the other battery is not present
or has previously alarmed. The LTC1760 will autono-
mously try to restore power by entering 3-Diode mode.
The 3-Diode mode will ignore TERMINATE_DISCHARGE
and FULLY_DISCHARGED alarms.
4.3 Power-By Algorithm When a Battery is Being
Calibrated
During battery calibration, the battery being calibrated is
the only device powering the system. This will be reflected
in the reported POWER_BY[4:1] bits. See “Section 5” for
more information on battery calibration.
U
4.4 Power-By Reporting
The following tables illustrate how BatterySystem
State(POWER_BY_BAT[4:1]) interprets power path
conditions.
Power Reporting for Batteries Being Calibrated
AC_PRESENT CALIBRATE_BAT2 CALIBRATE_BAT2 POWER_BY_BAT[4:1]
*States not shown are not allowed
Power Reporting as a Function of Battery Presence
AC_PRESENT PRESENT_BAT2 PRESENT_BAT1 POWER_BY_BAT[4:1]
Power Reporting with AC_PRESENT Low and both Batteries
Present, as a Function of Power Alarms.
Note 1: A power alarm means that ALARM() has returned
TERMINATE_DISCHARGE=1 or FULLY_DISCHARGED_ALARM=1
Power Reporting When
BatterySystemStateCont(POWER_NOT_GOOD) is High
and the LTC1760 has Autonomously Entered 3-Diode Mode
AC_PRESENT
AC_PRESENT PRESENT_BAT2 PRESENT_BAT1 POWER_BY_BAT[4:1]
1
1
1
1
0
0
0
0
0
0
0
0
1
0
0
0
0
1
1
1
1
POWER ALARM POWER ALARM
BATTERY 2
(NOTE 1)
0
0
1
X
0
0
1
1
0
0
1
1
X
0
0
1
1
0
0
1
1
BATTERY 1
(NOTE 1)
0
1
0
X
0
1
0
1
0
1
0
1
X
0
1
0
1
0
1
0
1
LTC1760
POWER_BY_BAT[4:1]
'b0000
'b0001
'b0010
'b0000
'b0000
'b0001
'b0010
'b0011
'b0011
'b0010
'b0001
'b0011
'b0000
'b0000
'b0001
'b0010
'b0011
'b0000
'b0000
'b0000
'b0000
27
1760f