LP3913 Datasheet, PDF (61/70 Pages) Texas Instruments – Power Management IC for Flash Memory-Based Portable Media Players

LP3913
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Resistors
SNVS489I – NOVEMBER 2006 – REVISED SEPTEMBER 2013
Battery Thermistor
The LP3913 battery thermistor bias provided by the T_S pin is tailored to thermistors with the following
specification:
• Negative Temperature Coefficient
• 100 kΩ resistance
A suitable solution is available from AVX thermistors:
AVXNB21250104 http://www.avxcorp.com/docs/Catalogs/nb21-23.pdf
I²C Pullup Resistors
I²C_SDA, I²C_SCL terminals need to have pullup resistors connected to the V_DDIO pin. V_DDIO must be connected
to a power supply that is less than or equal to V_DD, such as Buck2. The values of the pull-up resistors (typ. ≈1.8
kΩ) are determined by the capacitance of the bus. Too large of a resistor combined with a given bus capacitance
will result in a rise time that would violate the max rise time specification. Too small of a resistor will result in a
contention with the pull-down transistor on either slave(s) or master.
R_IREF Resistor
The current through this resistor is used as a reference current that biases many analog circuits inside the
LP3913 and needs to have a resistance of 121 kΩ ±1%
R_ISENSE Resistor
The current through this resistor is used as a reference current for the charge current. The accuracy of the ADC
is dependent on the tolerance of this resistor. R_ISENSE needs to have a resistance of 4.64 kΩ ±1% tolerance.
Operation without I²C Interface
Operation of the LP3913 without the I²C interface is possible if the system can operate with default values for the
DC/DC converters and the charger. (Read below: Factory programmable options). The I²C-less system must use
the POWERACK pin to power cycle the LP3913.
I²C Master Power Concern
The processor that contains the I²C master should 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 could accidentally disable, in which case the processor should be able to recognize that
communication has been broken and then power down the system to allow for a clean restart.
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 will eventually discharge the battery such that its extra power will no longer be sufficient to
properly operate the system. This will be the case when the system is for instance operated from a USB host
with a 100 mA current limit.
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