Datasheet

LTC4071
13
4071fc
Figure 6. Simple Photovoltaic Charger
Figure 7. Piezoelectric Energy Harvester with Battery Backup
LTC4071
BAT
GND
Li-Ion
BATTERY
V
CC
+
4071 F07
LTC4071
LTC3588-1
BAT
LBSEL
LBSEL
GND GND
PFCB-W14
Li-Ion
BATTERY
V
CC
+
1µF
PZ1
PZ2
D1
D0
SW
V
OUT
V
IN2
4.7µF
3.3V
SYSTEM
LOAD
100µF
10µH
CAPV
IN
V
IN2
22µF
1µF
MMSD4148T1
15k
applicaTions inForMaTion
the four input 249k resistors are sized for acceptable UL
leakage in the event that one of the resistors short. Here,
the LTC4071 will fully charge the battery from the AC line
while meeting the UL specification with 104µA of available
charge current.
A simple photovoltaic (PV) application for the LTC4071
is illustrated in Figure 6. At low V
CC
voltage, PV current
flows to both the system at V
CC
as well as the battery.
When V
CC
reaches the programmed float voltage (4.1V
with ADJ floating) then the LTC4071 shunts excess current
not used by the load, limiting V
CC
to 4.1V and effectively
reducing the battery charge current to zero. If the PV cells
stop supplying current, the battery supports the load at
V
CC
through the LTC4071. Add a diode in series with the
PV cells to prevent reverse leakage of the PV cells from
draining the battery. If the battery discharges to the point
where V
CC
falls below V
LBD
(3.2V with LBSEL tied to
GND) the LTC4071 disconnects the load from the battery
to protect the battery from over discharge.
Typically, solar cells are inherently limited in current, but
this circuit may require a resistor, R
IN
, in series with the
LTC4071 for high current solar cells. Select R
IN
such that
the LTC4071 never needs to shunt more than 50mA.
The simple schematic in Figure 7 illustrates a complete
piezoelectric energy harvesting application using the
LTC4071 to charge and protect Li-Ion cells along with the
LTC3588-1 to rectify and regulate energy generated from
a piezoelectric generator to a fixed 3.3V load.
LTC4071
BAT
NTCBIAS
NTC
LBSEL
ADJ
1µF
GND
DS16003
Li-Ion
V
CC
+
4071 F06
FLOAT
* NTHS0402N02N1002F
** JAMECO 171061
10k
T*
SYSTEM LOAD
**
**
**
**
+
–
+
–
+
–
+
–