LTC3459_07 Datasheet, PDF (9/12 Pages) Linear Technology – 10V Micropower Synchronous Boost Converter

LTC3459
TYPICAL APPLICATIONS
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 R_DS(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.
The LTC3459 is designed to control peak inductor current
when V_IN is greater than or less than V_OUT. This allows
current to be controlled during start-up in a boost applica-
tion, for example, or V_OUT to be regulated below V_IN 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 V_OUT is less than ~3.5V, the body of the internal
synchronous P-channel MOSFET rectifier is connected to
V_IN, and the SW pin rises a diode above V_IN when current
is delivered to the load. While efficiency is compromised
in this mode of operation, current to the SuperCap is
5V from Li-Ion Input
V_IN
2.5V TO 4.2V
+
Li-Ion
1μF
BATTERY
15μH*
OFF ON
SW
V_IN
V_OUT
LTC3459
SHDN FB
GND
*COILCRAFT DO3314
1M
332k
47pF
V_OUT
5V
4.7μF
3459 TA04a
100
V_OUT = 5V
90
80
70
60
V_IN = 4.2V
V_IN = 2.5V
V_IN
3.3V TO 5V
1μF
50
0.01
10V from 3.3V or 5V Input
0.1
1
10
100
I_LOAD (mA)
3459 TA04b
33μH*
OFF ON
SW
V_IN
V_OUT
LTC3459
SHDN FB
GND
2M
280k
47pF
V_OUT
10V
4.7μF
*COILCRAFT DO3314
3459 TA05a
100
V_OUT = 10V
90
80
70
60
V_IN = 5V
V_IN = 3.3V
50
0.01
0.1
1
10
I_LOAD (mA)
100
3459 TA05b
3459fc
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