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LTC3459EDC-PBF Datasheet(PDF) 9 Page - Linear Technology |
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LTC3459EDC-PBF Datasheet(HTML) 9 Page - Linear Technology |
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9 / 12 page  LTC3459 9 3459fc Very low operating quiescent current and synchronous operation allow for greater than 85% conversion efficiency in many applications. Lower output voltages will result in lower efficiencies since the N- and P-channel RDS(ON)s will increase. The switching frequency and output power capability of the LTC3459 are also dependant on input and output voltages. Charging a SuperCap® SuperCaps have become a popular alternative to NiCd batteries as back-up power sources in portable equip- ment. Capacitance values of one farad and higher are achievable in small package sizes with leakage currents in the low microamps. SuperCaps are typically charged at low currents for several minutes until they reach the required back-up voltage. TYPICAL APPLICATIONS 5V from Li-Ion Input The LTC3459 is designed to control peak inductor current when VIN is greater than or less than VOUT. This allows current to be controlled during start-up in a boost applica- tion, for example, or VOUT to be regulated below VIN when powered from a fresh battery. Peak current control makes the LTC3459 an ideal candidate for charging a back-up source such as a SuperCap. Figure 5 shows an application where the LTC3459 is used to charge a two-farad, 5V Su- perCap from a 3.3V input. A NiCd battery could be charged by the LTC3459 as well, but that application may require additional circuitry for proper charge termination. When VOUT is less than ~3.5V, the body of the internal synchronous P-channel MOSFET rectifier is connected to VIN, and the SW pin rises a diode above VIN when current is delivered to the load. While efficiency is compromised in this mode of operation, current to the SuperCap is 10V from 3.3V or 5V Input SW 15μH* VIN 1M VOUT 5V 4.7μF 47pF 1μF LTC3459 SHDN VOUT FB Li-Ion BATTERY VIN 2.5V TO 4.2V OFF ON GND 332k 3459 TA04a *COILCRAFT DO3314 + ILOAD (mA) 60 70 80 90 100 0.01 1 10 100 3459 TA04b 50 0.1 VOUT = 5V VIN = 4.2V VIN = 2.5V SW 33μH* VIN 2M VOUT 10V VIN 3.3V TO 5V 4.7μF 47pF 1μF LTC3459 SHDN VOUT FB OFF ON GND 280k 3459 TA05a *COILCRAFT DO3314 ILOAD (mA) 60 70 80 90 100 0.01 1 10 100 3459 TA05b 50 0.1 VOUT = 10V VIN = 3.3V VIN = 5V |
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