LTC3331_15 Datasheet, PDF (27/34 Pages) Linear Technology – Nanopower Buck-Boost DC/DC with Energy Harvesting Battery Charger

LTC3331
APPLICATIONS INFORMATION
For applications where more charging current is available
a resistor tied to V_IN or the circuit of Figure 7 can be used
to provide up to 10mA to the battery. The circuit of Figure 7
uses the CHARGE pin to only allow charging when the
energy harvester is sleeping. For applications requiring
even more charging current, the LTC3331 can be paired
with the LTC4071 shunt battery charger connected at the
BB_IN pin.
LTC3331 System Solutions
V_IN
Q2
LTC3331 ^CMPT3906E
R2
1M
CHARGE
Q1A
NDC7001C
R3 R4
1M 100k
R1
56.2Ω
Q1B
NDC7001C
CMOSH-3
The LTC3331 can be paired with other Linear Technology low
quiescent current integrated circuits to form a multirail sys-
tem. Figure 8 shows an LTC3331 powering an LTC3388-3
from its 5V output. The LTC3388-3, an 800nA Buck
converter, is configured here to produce a negative 5V
rail by tying the V_OUT pin to ground and tying its GND pin
to the regulated –5V output. The result is a ±5V energy
harvesting power supply with battery backup.
Higher Efficiency Battery Powered Buck
BB_IN
3331 F07
Figure 7
MIDE V25W
22µF
25V
AC2
V_IN
1µF
6.3V
CAP
V_IN2
LTC3331
AC1
SWA
SWB
SW
22µH
22µH
If the battery voltage will always be higher than the regu-
lated output of the LTC3331 then the battery powered
buck-boost will always run in buck mode. In this case the
inductor that is usually placed between SWA and SWB
can go directly to V_OUT from SWA, bypassing internal
switch M4 of the buck-boost (Figure 9). This will reduce
conduction losses in the converter and improve the ef-
ficiency at higher loads.
4.7µF
UV3
6.3V
UV2
UVLO RISING = 12V**
UVLO FALLING = 11V
UV1
IPEAK_BB = 250mA
UV0
4.1V
+
Li-ION
BAT_IN
1µF
6.3V
CHARGE
68k
BAT_OUT
V_OUT
SCAP
BAL
PGVOUT
EH_ON
V_IN3
IPK2
IPK1
IPK0
OUT2
OUT1
22µF
6.3V
1µF
6.3V
2.2µF
10V
4.7µF
6.3V
V_IN
PGOOD
LTC3388-3*
CAP
V_IN2
SW
EN
V_OUT
D1
D0
STBY
GND
22µH
5V
22µF
6.3V
–5V
3331 F08
22µF
BB_IN
OUT0
6.3V
FLOAT1 FLOAT0 LBSEL SHIP GND
0.1µF
6.3V
*EXPOSED PAD MUST BE ELECTRICALLY ISOLATED FROM
SYSTEM GROUND AND CONNECTED TO THE –5V RAIL
**FOR PEAK POWER TRANSFER, CENTER THE UVLO WINDOW
AT HALF THE RECTIFIED OPEN CIRCUIT VOLTAGE OF THE PIEZO
Figure 8. Dual ±5V Power Supply
For more information www.linear.com/LTC3331
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