LP3910 Datasheet, PDF (40/72 Pages) Texas Instruments – Power Management IC for Hard-Drive-Based Portable Media Players

LP3910
SNVS481M – NOVEMBER 2006 – REVISED DECEMBER 2015
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8.3.7 Power-On-Reset
The LP3910 is equipped with an internal power-on-reset (POR ) circuit that resets the logic when V_DD < V_POR.
This ensures that the logic is properly initialized when V_DD rises above the minimum operating voltage of the
logic and the internal oscillator that clocks the sequential logic in the control section.
8.3.8 Thermal Shutdown and Thermal Alarm
An internal temperature sensor monitors the junction temperature of the LP3910. This sensor forcibly invokes
standby mode in the unusual case of the junction temperature of the silicon exceeding the normal operating level
due to excessive loads on all power regulators, the Li-ion charger, or due to an abnormally high ambient
temperature. The thermal shutdown threshold is 160°C.
The thermal shutdown is preceded by a thermal alarm that generates an interrupt request if unmasked. The
temperature threshold for triggering the alarm is 115°C.
8.3.9 NRST Pin
The NRST pin is an open-drain output and is active low during standby, power-off and charger standby modes.
The NRST timing is determined by a factory programmable counter.
8.3.10 Operation Without I²C Interface
Operation of the LP3910 without the I²C interface is possible if the system can operate with default values for the
DC-DC converters and the charge (see Table 3). The I²C-less system must use the POWERACK pin to power
cycle the LP3910.
8.3.11 I²C Master Power Concern
The processor that contains the I²C master must be powered by BUCK1 or LDO2 as these converters require no
I²C access to enable/disable them. If the I²C master were to be powered by a DC-DC converter that is
enable/disabled through a control register, then a corrupted application software execution could by accident
disable the power to the I²C master, which in this case has no means to recover. It is possible that the regulator
connected to V_DDIO may accidentally disable, in which case the processor should recognize that communication
has been broken, then power down the system to allow for a clean restart.
8.3.12 System Operation When the Load Current Exceeds the USB or Adapter Current Limit
In the event that the system requires current that exceeds the current limit of either the USB or the adapter
source, then the battery can provide the extra power provided that it has been charged. It is clear that a long
sustained overload eventually discharges the battery such that its extra power is no longer be sufficient to
properly operate the system. This is the case when the system is for instance operated from a USB host with a
100-mA current limit.
8.3.13 Power Routing
The LP3910 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 (V_FULLRATE).
• 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:
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
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