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LTC3330

3330p

For more information www.linear.com/LTC3330

OVERVIEW

The LTC3330 combines a buck switching regulator and

a buck-boost switching regulator to produce an energy

harvestingsolutionwithbatterybackup.Theconvertersare

controlled by a prioritizer that selects which converter to

usebasedontheavailabilityofabatteryand/orharvestable

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

currentpowersupplytailoredtoenergyharvestingapplica-

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 VIN 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 VIN 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

operaTion

Figure 1. Ideal VIN, VIN2 and CAP Relationship

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 VIN2, are generated from VIN

and are used to drive the high side PMOS and low side

NMOS of the buck converter, respectively. Additionally the

VIN2 rail serves as logic high for the UVLO threshold select

bits UV[3:0]. The VIN2 rail is regulated at 4.8V above GND

while the CAP rail is regulated at 4.8V below VIN. These are

not intended to be used as external rails. Bypass capaci-

tors are connected to the CAP and VIN2 pins to serve as

energy reservoirs for driving the buck switches. When VIN

is below 4.8V, VIN2 is equal to VIN and CAP is held at GND.

Figure 1 shows the ideal VIN, VIN2 and CAP relationship.

VIN (V)

3330 F01

VIN

VIN2

CAP

BUCK OPERATION

The buck regulator uses a hysteretic voltage algorithm

to control the output through internal feedback from the

VOUT 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 VIN,

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