LTC3331_15 Datasheet, PDF (24/34 Pages) Linear Technology – Nanopower Buck-Boost DC/DC with Energy Harvesting Battery Charger

LTC3331
APPLICATIONS INFORMATION
CAP, V_IN2, and V_IN3 Capacitors
A 1μF or larger capacitor must be connected between V_IN
and CAP and a 4.7μF capacitor must be connected between
V_IN2 and GND. These capacitors hold up the internal rails
during buck switching and compensate the internal rail
generation circuits. In applications where the voltage at V_IN
is limited to less than 6V, the CAP pin can be tied to GND
and the V_IN2 pin can be tied to V_IN as shown in Figure 6.
An optional 5.6V Zener diode can be connected to V_IN
to clamp V_IN in this scenario. The leakage of the Zener
diode below its clamping voltage should be considered
as it could be comparable to the quiescent current of the
LTC3331. This circuit does not require the capacitors on
V_IN2 and CAP, saving two components and allowing for a
lower voltage rating for the single V_IN capacitor.
A 0.1µF bypass capacitor must be connected from V_IN3
to ground. V_IN3 is an internal rail that is shared by both
the buck and buck-boost. It is not intended for use as a
system rail. It is used as a the logic high reference level
for the IPK[2:0] and OUT[2:0] digital inputs. In the event
that these pins are dynamically driven in the application,
external inverters may be needed and they must use V_IN3
as a rail. However, care must be taken not to overload
V_IN3 and the quiescent current of such logic should be
kept minimal. The output resistance of the V_IN3 pin is
typically 15kΩ.
+
SOLAR
PANEL
–
AC2
AC1
V_IN
5.6V
22µF
(OPTIONAL)
6.3V
V_IN2
CAP
LTC3331
SWA
SWB
SW
UV3
UV2
UVLO RISING = 4V
UVLO FALLING = 3V
UV1
IPEAK_BB = 150mA
UV0
V_OUT
SCAP
BAL
PGVOUT
4.2V
+
Li-ION
BAT_IN
1µF
6.3V
CHARGE
12k
EH_ON
V_IN3
IPK2
IPK1
IPK0
OUT2
BAT_OUT
OUT1
22µF
BB_IN
OUT0
6.3V
FLOAT1 FLOAT0 LBSEL SHIP GND
+
SOLAR
PANEL
–
33µH
22µH
1.8V
22µF
6.3V
0.1µF
6.3V
3331 F06
Figure 6. Low Voltage Solar Harvester with Reduced Component Count (V_IN < 6V)
24
For more information www.linear.com/LTC3331
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