LP3910SQ-AN Datasheet, PDF (39/60 Pages) National Semiconductor (TI) – Power Management IC for Hard Drive Based Portable Media Players

the safety timer is a maximum of 10 hours minus the time in
prequalification.
When the timer times out of uninterrupted charging, an IRQ
is generated to alert system processor. The status of the timer
can also be polled by reading the IRQ register if the system
doesn’t support hardware interrupts.
The Safety timer resets and starts counting from zero upon
the following events:
1. Power ON (through connecting valid power to either
USBPWR or CHGN_IN pins).
2. Interchanging USBPWR and CHG_IN sources
3. The voltage of a charged battery drops below the restart
value and the charger is enabled
4. Disabling and re-enabling of the charger by toggling bit
D1 of the Charge Control Register
5. Emerging from Thermal Shutdown
6. Emerging from a battery temperature out-of-range and
the charger is enabled
CHSPV Register (02)h Charger Supervisor Register
Access
Data
D7–6
Read only
Reserved
D5
r/w
LED Current
0: 5 mA
1: 10 mA
D4
r/w
LED ENABLE
0: Disabled
1:Enabled
Reset
n/a
1
1
POWER ROUTING
The LP3910SQ-AN power can originate from three different
sources: Adapter power, USB power or battery power. The
objective of the power routing is to be able to:
• Operate the portable system from external power
regardless of the battery voltage.
• Operate the portable system from USBPWR when the
battery exceeds the Full Rate Qualification Threshold
voltage (Vfullrate).
• Concurrently charging and operating the system when
external power is present
• Seamless selection of Adapter or USB power as the
primary external power source
Power Routing supports 4 modes:
7. Emerging from USB suspend mode when charging with
USB power
Charging Maintenance
When a fully charged battery is being loaded by the system
while the external power is present and while bit D1 in the
charge control register is set to a 1 (Charge enable) then the
charging will restart when the battery voltage drops below the
charging restart threshold. The value of the threshold de-
pends on the termination voltage according to the following
table:
Vterm
4.1V
4.2V
4.38V
Charging restart voltage
3.9V
4.0V
4.2V
D3
r/w
Battery
temperature
range
0: 0°C–50°C
1: 0°C–45°C
0
D2–0
Charger status
Stat2 Stat1 Stat0
0
0
0
Charger is off
0
0
1
Prequalification
0
1
0
Constant current
charging
0
1
1
Constant voltage
charging
1
0
0
Error
1
0
1
Charge cycle
complete
1
1
0
Safety Timer Expired
1
1
1
EOC / Top-off
2’b000
1. A regulated external adapter power is present and
concurrently supplies the system power and the battery
charger.
2. USB power is present and supplies the system and the
battery.
3. USB power is present but the system demand exceeds
the USB current limit, so that the battery provides the
additional power to operate the system.
4. The battery is the sole supply source to the system when
no external power source is present
The current flows in the different modes are realized through
internal FETS and an external Schottky as illustrated as fol-
lows:
39
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