Datasheet LTC3107 (Analog Devices) - 10

LTC3107
operaTion VAUX
When enough harvested energy is available to power the The active circuits within the LTC3107 are powered from load, VOUT will be hysteretically regulated to a voltage VAUX, which should be bypassed with a capacitor of 10µF typically 30mV below VBAT, and the battery will not be minimum. used. In this condition, the current drain on the battery is only 80nA typical. The quiescent current draw on VAUX is typically just 6µA. If harvested energy is available, this current will come from In a typical application, a bulk decoupling capacitor (usually the harvesting source. If there is no harvesting energy a few hundred microfarads) is connected to VOUT to allow available, the VAUX supply current will come from V it to ride-through small, periodic load transients typical of BAT. a wireless sensor application. If the VOUT capacitor is sized A shunt regulator limits the maximum voltage on VAUX appropriately (see the Applications Information section to 4.3V typical. It shunts to ground any excess harvested for more detail), and the average harvested input power current into VAUX when there is no load on the converter exceeds the average load power, then battery energy will or the input source is generating more power than is never be used. required by the load. If the optional storage capacitor is connected to VSTORE, then the excess current will be used
BAT_OFF
to charge the storage capacitor, and current will not be The BAT_OFF output is a digital output with an internal shunted to ground until the storage capacitor is charged pull-up to V up to the 4.3V clamp level. OUT. BAT_OFF is an indicator of when the battery is being used to help maintain VOUT. If BAT_OFF
Voltage Reference
is high, it indicates that VOUT (and VLDO) are being powered entirely by the harvested input power (including The LTC3107 includes a precision, micropower reference, the VSTORE capacitor), and the battery is not being used. for accurate regulated output voltages. This reference In this case, the battery current draw is only 80nA typical. becomes active as soon as VAUX exceeds 1.9V. When BAT_OFF goes low, it indicates that the battery is being used to help maintain V
Low Dropout Linear Regulator (LDO)
OUT and VLDO in regulation. This indicates that either there is no harvested energy The LTC3107 includes a low current LDO to provide a available, or it is insufficient to power the load entirely. regulated 2.2V output for powering low power processors. If the COUT capacitor is not sized properly, the BAT_OFF The LDO is powered by the higher of VAUX or VOUT, and indicator may go low during a pulsed load event, to in- requires a minimum of 2.2µF ceramic decoupling capacitor. dicate that current is being drawn from the battery. See Larger capacitor values can be used without limitation. the Applications Information section of this data sheet for guidance on sizing the C If the LDO is not being used, the VLDO pin should be tied OUT capacitor. to VAUX.
VSTORE VOUT
The VSTORE output can be used to charge an optional storage capacitor, after V The LTC3107 is designed to fit seamlessly into existing OUT has reached regulation. The VSTORE capacitor value can range from hundreds of applications that run from a primary battery, while adding micro-farads up to Farads. Once V the benefit of energy harvesting to increase the life of the OUT has reached regula- tion, the VSTORE output will be allowed to charge up to battery. The main output voltage on VOUT is designed to the maximum VAUX voltage if excess harvested energy is track the battery voltage on VBAT. If no harvested energy available. The storage capacitor on VSTORE can be used is available, or the energy is insufficient to maintain VOUT, to power the system in the event that the input source is then VOUT will be hysteretically regulated 230mV below lost, or is unable to provide the current demanded by the VBAT by periodically connecting it to VBAT. loads on VOUT and VLDO, or simply to supplement the 3107f 10 For more information www.linear.com/LTC3107 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts