LTC3105 OPERATION When the converter is placed in shutdown mode, the LDO capability at heavy load by adjusting the peak and valley is forced into reverse-blocking mode with reverse current of the inductor current as a function of load. Lowering the limited to under 1µA. After the shutdown event has ended, peak inductor current to 100mA at light load optimizes the LDO remains in reverse-blocking mode until VAUX has efficiency by reducing conduction losses. As the load risen above the LDO voltage. increases, the peak inductor current is automatically in- creased to a maximum of 500mA. At intermediate loads, MPPC Operation the peak inductor current can vary between 100mA to The maximum power point control circuit allows the user 500mA. This function is overridden by the MPPC function to set the optimal input voltage operating point for a given and will only be observed when the power source can power source. The MPPC circuit dynamically regulates deliver more power than the load requires. the average inductor current to prevent the input voltage from dropping below the MPPC threshold. When V PGOOD Operation IN is greater than the MPPC voltage, the inductor current is The power good output is used to indicate that VOUT is increased until VIN is pulled down to the MPPC set point. in regulation. PGOOD is an open-drain output, and is If VIN is less than the MPPC voltage, the inductor current disabled in shutdown. PGOOD will indicate that power is reduced until VIN rises to the MPPC set point. is good at the beginning of the first sleep event after the output voltage has risen above 90% of its regulation Automatic Power Adjust value. PGOOD remains asserted until VOUT drops below The LTC3105 incorporates a feature that maximizes ef- 90% of its regulation value at which point PGOOD will ficiency at light load while providing increased power pull low. APPLICATIONS INFORMATION Component Selection should be large enough to allow the converter to complete Low DCR power inductors with values between 4.7µH start-up mode using the energy stored in the input ca- and 30µH are suitable for use with the LTC3105. For pacitor. When using bulk input capacitors that have high most applications, a 10µH inductor is recommended. In ESR, a small valued parallel ceramic capacitor should be applications where the input voltage is very low, a larger placed between VIN and GND as close to the converter value inductor can provide higher efficiency and a lower pins as possible. start-up voltage. In applications where the input voltage A 1µF ceramic capacitor should be connected between is relatively high (VIN > 0.8V), smaller inductors may be AUX and GND. Larger capacitors should be avoided to used to provide a smaller overall footprint. In all cases, minimize start-up time. A low ESR output capacitor should the inductor must have low DCR and sufficient saturation be connected between V current rating. If the DC resistance of the inductor is too OUT and GND. The main output capacitor should be 10µF or larger. The main output can high, efficiency will be reduced and the minimum operating also be used to charge energy storage devices including voltage will increase. tantalum capacitors, supercapacitors and batteries. When Input capacitor selection is highly important in low voltage, using output bulk storage devices with high ESR, a small high source resistance systems. For general applications, valued ceramic capacitor should be placed in parallel and a 10µF ceramic capacitor is recommended between VIN located as close to the converter pins as possible. and GND. For high impedance sources, the input capacitor 3105fb 10 For more information www.linear.com/LTC3105 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 Application Related Parts
