LTC3588-1 Datasheet, PDF (14/20 Pages) Linear Technology – Piezoelectric Energy Harvesting Power Supply

LTC3588-1
APPLICATIONS INFORMATION
This is true for output capacitors on the order of 100μF
or larger, but as the output capacitor decreases towards
10μF delays in the internal sleep comparator along with
the load current may result in the V_OUT voltage slewing
past the ±12mV thresholds. This will lengthen the sleep
time and increase V_OUT ripple. A capacitor less than 10μF
is not recommended as V_OUT ripple could increase to an
undesirable level.
If transient load currents above 100mA are required then a
larger capacitor can be used at the output. This capacitor
will be continuously discharged during a load condition
and the capacitor can be sized for an acceptable drop in
V_OUT:
( ) ^C_OUT ⁼
V_OUT+ − V_OUT–
I_LOAD − I_BUCK
t_LOAD
Here V_OUT+ is the value of V_OUT when PGOOD goes high
and V_OUT– is the desired lower limit of V_OUT. I_BUCK is the
average current being delivered from the buck converter,
typically I_PEAK/2.
A standard surface mount ceramic capacitor can be used
for C_OUT, though some applications may be better suited
to a low leakage aluminum electrolytic capacitor or a
supercapacitor. These capacitors can be obtained from
manufacturers such as Vishay, Illinois Capacitor, AVX,
or CAP-XX.
Inductor
The buck is optimized to work with an inductor in the range
of 10μH to 22μH, although inductor values outside this
range may yield benefits in some applications. For typical
applications, a value of 10μH is recommended. A larger
inductor will benefit high voltage applications by increasing
the on-time of the PMOS switch and improving efficiency
by reducing gate charge loss. Choose an inductor with a
DC current rating greater than 350mA. The DCR of the
inductor can have an impact on efficiency as it is a source
of loss. Tradeoffs between price, size, and DCR should be
evaluated. Table 3 lists several inductors that work well
with the LTC3588-1.
Table 3. Recommended Inductors for LTC3588-1
INDUCTOR
TYPE
MAX MAX
L I_DC DCR
(μH) (mA) (Ω)
SIZE in mm
(L × W × H)
CDRH2D18/LDNP 10 430 0.180 3 × 3 × 2
107AS-100M
10 650 0.145 2.8 × 3 × 1.8
EPL3015-103ML 10 350 0.301 2.8 × 3 × 1.5
MLP3225s100L 10 1000 0.130 3.2 × 2.5 × 1.0
XLP2010-163ML 10 490 0.611 2.0 × 1.9 × 1.0
SLF7045T
100 500 0.250 7.0 × 7.0 × 4.5
MANU-
FACTURER
Sumida
Toko
Coilcraft
TDK
Coilcraft
TDK
V_IN2 and CAP Capacitors
A 1μF capacitor should be connected between V_IN and
CAP and a 4.7μF capacitor should 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 input source
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 Zener voltage should be considered as it may
be comparable to the quiescent current of the LTC3588-1.
This circuit does not require the capacitors on V_IN2 and
CAP, saving components and allowing a lower voltage
rating for the single V_IN capacitor.
PIEZO SYSTEMS T220-A4-503X
5.6V
(OPTIONAL)
10μF
6V
PZ1
PZ2
V_IN
PGOOD
V_{IN2 LTC3588-1}
CAP
SW
D1
V_OUT
D0
GND
10μH
PGOOD
V_OUT
1.8V
10μF
6V
35881 F06
Figure 6. Smallest Solution Size 1.8V Low Voltage Input
Piezoelectric Power Supply
35881f
14