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Power Path Logic: Priority Algorithm
Input Current Limit
TPS65810
TPS65811
SLVS658B – MARCH 2006 – REVISED FEBRUARY 2007
Table 4. System Status Detection, Charger and Power Path Section
AC input voltage detected V(AC) – V(BAT) > V
IN(DT)
USB input voltage detected V(USB) – V(BAT) > V
IN(DT)
AC overvoltage detected V(AC) > V
OVP
USB overvoltage detected V(USB) > V
OVP
AC PIN TO OUT pin OR USB TO OUT PIN short detected V(OUT) < V
INOUTSH
BAT pin to OUT pin short detected V(BAT) - V(OUT) > V
BATOUTSH
Battery supplement mode need detected V(BAT) – V(OUT) > V
SUP
Blank BAT to OUT short circuit detection V(DPPM) < 1V
The system power bus supply is automatically selected by the power path control logic, following an internal
algorithm. The power path function detects an external input power connection when the input voltage exceeds
the battery pack voltage. It also detects a supplement mode need (battery switch must be turned ON) when the
system voltage (OUT pin) is below the battery voltage. A connected and non-selected external supply or the
battery is automatically switched to the system bus, following the priority algorithm, when the external supply
currently selected is disconnected from the system.
The input power priority is hard-wired internally, with the AC input having the higher priority, followed by the USB
input (2
nd
) and the battery pack (3
rd
). Using the I
2
C CHG_CONFIG register control bit CE the user can override
the power path algorithm, connecting the battery to the system power bus. Care must be taken when using the
battery-to-system connection option, as the system power bus is not connected back to the AC or USB inputs
(even if those are detected) when the battery is removed. Table 5 describes the priority algorithm.
Table 5. Power Path Control Logic Priority Algorithm
CE BIT EXTERNAL SUPPLY SWITCH MODE SYSTEM POWER
(I
2
C CHG_CONFIG Register) DETECTED SOURCE
AC USB AC USB Battery
HI YES NO ON OFF ON if Supplement mode is AC
required, OFF otherwise
NO YES OFF ON USB
YES YES ON OFF AC
NO NO OFF OFF BATTERY
LO XX XX OFF OFF ON BATTERY
The power path status is stored in register CHG_STAT.
The USB input current is limited to the maximum value programmed by the host, using the I
2
C interface. If the
system current requirements exceed the input current limit, the output voltage collapses, the charge current is
reduced, and finally, the supplement mode is set. The input current limit value is set with the I
2
C charge control
register bits PSEL and ISET2, and it is applied to the USB input ONLY. The AC input current limit is fixed to the
internal short circuit limit value.
Table 6. Charge Current Scaling via I
2
C
PSEL (I
2
C) ISET2 (I
2
C) INPUT CURRENT LIMIT
USB AC
LO LO 100 mA 2.75 A
LO HI 500 mA 2.75 A
HI LO 2.75 A 2.75 A
HI HI 2.75 A 2.75 A
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