LTC3331_15 Datasheet, PDF (28/34 Pages) Linear Technology – Nanopower Buck-Boost DC/DC with Energy Harvesting Battery Charger

LTC3331
APPLICATIONS INFORMATION
MIDE V25W
22µF
25V _4.7µF
1µF
6.3V
6.3V
UVLO RISING = 12V*
UVLO FALLING = 11V
IPEAK_BB = 250mA
4.0V
+
Li-ION
1µF
6.3V
68k
22µF
6.3V
AC2
V_IN
CAP
V_IN2
UV3
UV2
UV1
UV0
LTC3331
AC1
SWA
SWB
SW
V_OUT
SCAP
BAL
PGVOUT
EH_ON
BAT_IN
CHARGE
BAT_OUT
BB_IN
V_IN3
IPK2
IPK1
IPK0
OUT2
OUT1
OUT0
FLOAT0 FLOAT1 LBSEL SHIP GND
22µH
22µH
1.8V
22µF
6.3V
0.1µF
6.3V
3331 F09a
100
V_OUT = 1.8V, BYPASS SWB
V_OUT = 1.8V, INCLUDE SWB
95
V_OUT = 3.3V, BYPASS SWB
V_OUT = 3.3V, INCLUDE SWB
90
85
80
75
2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2
BB_IN (V)
3331 F09b
Figure 9b. Efficiency Comparison Between
Normal Buck-Boost and Bypassed SWB
Configuration
*FOR PEAK POWER TRANSFER, CENTER THE UVLO WINDOW
AT HALF THE RECTIFIED OPEN CIRCUIT VOLTAGE OF THE PIEZO
Figure 9a. Higher Efficiency Battery-Powered Buck Regulator
Alternative Power Sources
The LTC3331 can accommodate a wide variety of input
sources. Figure 10 shows the LTC3331 internal bridge
rectifier connected to a 120V RMS AC line in series with
four 3.9k current limiting resistors. This produces a peak
current of 10mA with the LTC3331 shunt holding V_IN
at 20V. This current may be increased by reducing the
resistor values since the shunt can sink 25mA and the
bridge is rated for 50mA. An optional external Zener diode
(shown) may be required if the current exceeds 25mA. A
transformer may also be used to step down the voltage
and reduce the power loss in the current limiting resistors.
The 3.3k charging resistor charges the battery from V_IN
with approximately 5mA. This is a high voltage application
and minimum spacing between the line, neutral, and any
high voltage components should be maintained per the
applicable UL specification. For general off-line applica-
tions refer to UL Regulation 1012.
Figure 11 shows an application where copper panels are
placed near a standard fluorescent room light to capaci-
tively harvest energy from the electric field around the
light. The frequency of the emission will be double the
line frequency for magnetic ballasts but could be higher
if the light uses electronic ballast. The peak AC voltage
and the total available energy will scale with the size of
the panels used and with the proximity of the panels to
the electric field of the light.
The LTC3331 could also be used to wirelessly harvest
energy and charge a battery by using a transmitter and
receiver consisting of loosely coupled tuned resonant
tanks as shown in Figure 12.
Using EH_ON to Program V_OUT
The EH_ON output indicates whether the energy harvesting
input or the battery is powering the output. The application
3331fb
28
For more information www.linear.com/LTC3331