LTC3330 Datasheet, PDF (13/20 Pages) Linear Technology – Energy Harvesting DC/DC with Battery Backup Low Noise LDO Post Regulator

LTC3330
Operation
OVERVIEW
The LTC3330 combines a buck switching regulator and
a buck-boost switching regulator to produce an energy
harvesting solution with battery backup. The converters are
controlled by a prioritizer that selects which converter to
use based on the availability of a battery and/or harvestable
energy. If harvested energy is available the buck regula-
tor is active and the buck-boost is OFF. With an optional
LDO and supercapacitor balancer and an array of different
configurations the LTC3330 suits many applications.
BUCK CONVERTER
The synchronous buck converter is an ultralow quiescent
current power supply tailored to energy harvesting applica-
tions. It is designed to interface directly to a piezoelectric
or alternative A/C power source, rectify the input voltage,
and store harvested energy on an external capacitor while
maintaining a regulated output voltage. It can also bleed
off any excess input power via an internal shunt regulator.
INTERNAL BRIDGE RECTIFIER
An internal full-wave bridge rectifier accessible via the
differential AC1 and AC2 inputs rectifies AC sources
such as those from a piezoelectric element. The rectified
output is stored on a capacitor at the V_IN pin and can be
used as an energy reservoir for the buck converter. The
bridge rectifier has a total drop of about 800mV with
typical piezo-generated currents (~10μA), but is capable
of carrying up to 50mA. Either side of the bridge can be
operated independently as single-ended AC or DC inputs.
UNDERVOLTAGE LOCKOUT
When the voltage on V_IN rises above the UVLO rising
threshold the buck converter is enabled and charge is
transferred from the input capacitor to the output capaci-
tor. When the input capacitor voltage is depleted below
the UVLO falling threshold the buck converter is disabled.
These thresholds can be set according to Table 4 which
offers UVLO rising thresholds from 4V to 18V with large
or small hysteresis windows (see Table 4). Extremely low
quiescent current (450nA typical) in UVLO allows energy
to accumulate on the input capacitor in situations where
energy must be harvested from low power sources.
INTERNAL RAIL GENERATION
Two internal rails, CAP and V_IN2, are generated from V_IN
and are used to drive the high side PMOS and low side
NMOS of the buck converter, respectively. Additionally the
V_IN2 rail serves as logic high for the UVLO threshold select
bits UV[3:0]. The V_IN2 rail is regulated at 4.8V above GND
while the CAP rail is regulated at 4.8V below V_IN. These are
not intended to be used as external rails. Bypass capaci-
tors are connected to the CAP and V_IN2 pins to serve as
energy reservoirs for driving the buck switches. When V_IN
is below 4.8V, V_IN2 is equal to V_IN and CAP is held at GND.
Figure 1 shows the ideal V_IN, V_IN2 and CAP relationship.
18
16
14
12
V_IN
10
8
6
V_IN2
4
2
CAP
0
0
5
10
15
V_IN (V)
3330 F01
Figure 1. Ideal V_IN, V_IN2 and CAP Relationship
BUCK OPERATION
The buck regulator uses a hysteretic voltage algorithm
to control the output through internal feedback from the
V_OUT sense pin. The buck converter charges an output
capacitor through an inductor to a value slightly higher
than the regulation point. It does this by ramping the
inductor current up to 260mA through an internal PMOS
switch and then ramping it down to 0mA through an
internal NMOS switch. This efficiently delivers energy to
the output capacitor. The ramp rate is determined by V_IN,
For more information www.linear.com/LTC3330
3330p
13