LTC3588-1
Piezoelectric Energy
Harvesting Power Supply
FEATURESDESCRIPTIONn

The LTC®3588-1 integrates a low-loss full-wave bridge
rectiﬁer with a high efﬁciency buck converter to form acomplete energy harvesting solution optimized for highoutput impedance energy sources such as piezoelectrictransducers. An ultralow quiescent current undervoltage
lockout (UVLO) mode with a wide hysteresis window allows
charge to accumulate on an input capacitor until the buckconverter can efﬁciently transfer a portion of the stored
charge to the output. In regulation, the LTC3588-1 entersa sleep state in which both input and output quiescentcurrents are minimal. The buck converter turns on andoff as needed to maintain regulation.

950nA Input Quiescent Current (Output inRegulation – No Load)n 450nA Input Quiescent Current in UVLO
n 2.7V to 20V Input Operating Rangen Integrated Low-Loss Full-Wave Bridge Rectiﬁer
n Up to 100mA of Output Current
n Selectable Output Voltages of 1.8V, 2.5V, 3.3V, 3.6V
n High Efﬁciency Integrated Hysteretic Buck DC/DCn Input Protective Shunt – Up to 25mA Pull-Down at
VIN ≥ 20V
n Wide Input Undervoltage Lockout (UVLO) Rangen Available in 10-Lead MSE and 3mm × 3mm DFN
Packages

APPLICATIONSn

Piezoelectric Energy HarvestingElectro-Mechanical Energy Harvestingn Wireless HVAC Sensors
n Mobile Asset Tracking
n Tire Pressure Sensors
n Battery Replacement for Industrial Sensors
n Remote Light Switchesn Standalone Nanopower Buck RegulatornFour output voltages, 1.8V, 2.5V, 3.3V and 3.6V, are pin
selectable with up to 100mA of continuous output current;
however, the output capacitor may be sized to service ahigher output current burst. An input protective shunt set
at 20V enables greater energy storage for a given amountof input capacitance.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarksof Linear Technology Corporation. All other trademarks are the property of their respective
owners.

TYPICAL APPLICATION
100mA Piezoelectric Energy Harvesting Power Supply

LTC3588-1 3.3V Regulator Start-Up Proﬁle22

CSTORAGE = 22μF, COUT = 47μF
20 NO LOAD, IVIN = 2μA
18

ADVANCED CERAMETRICS PFC-W14

1μF
6V
CSTORAGE
25V
4.7μF
6V

PZ2

VIN

SW

LTC3588-1

10μH
VOUT
47μF
6V

VOUT

CAP

PGOOD

VIN2

D0, D1
GND
35881 TA01

2

OUTPUT
VOLTAGESELECT

VOLTAGE (V)

16
PZ1

14

VIN

12
10
8
6
4

VOUT

2

PGOOD = LOGIC 1

0

0

200

400
TIME (s)60035881 TA01b

35881f1

LTC3588-1
ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN
Low Impedance Source ....................... –0.3V to 18V*
Current Fed, ISW = 0A ...................................... 25mA†
PZ1, PZ2 ...........................................................0V to VIN
D0, D1.............. –0.3V to [Lesser of (VIN2 + 0.3V) or 6V]
CAP ......................[Higher of –0.3V or (VIN – 6V)] to VIN
VIN2 ....................–0.3V to [Lesser of (VIN + 0.3V) or 6V]* VIN has an internal 20V clamp† For t < 1ms and Duty Cycle < 1%,
Absolute Maximum Continuous Current = 5mA

VOUT ....................–0.3V to Lesser of (VIN2 + 0.3V) or 6V
PGOOD...............–0.3V to Lesser of (VOUT + 0.3V) or 6V
IPZ1, IPZ2 ..............................................................±50mA
ISW .......................................................................350mA
Operating Junction Temperature Range(Notes 2, 3) ................................................–40 to 125°C
Storage Temperature Range.......................–65 to 125°C
Lead Temperature (Soldering, 10 sec)
MSE Only .......................................................... 300°C

PIN CONFIGURATIONTOP VIEWTOP VIEW

10 PGOOD

PZ1

1

PZ2

2

CAP

3

VIN

4

7 VIN2SW

5

6 VOUT

11
GND

PZ1 1
PZ2 2
CAP 3
VIN 4
SW 5

9 D0
8 D1

11
GND

10
9
8
7
6

PGOOD
D0
D1
VIN2
VOUT

MSE PACKAGE
10-LEAD PLASTIC MSOPDD PACKAGE
10-LEAD (3mm s 3mm) PLASTIC DFNTJMAX = 125°C, θJA = 43°C/W, θJC = 7.5°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCBTJMAX = 125°C, θJA = 45°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCBORDER INFORMATIONLEAD FREE FINISH

TAPE AND REELPART MARKING*PACKAGE DESCRIPTIONTEMPERATURE RANGE

LTC3588EDD-1#PBF

LTC3588EDD-1#TRPBF

LFKY

10-Lead (3mm × 3mm) Plastic DFN–40°C to 85°C

LTC3588IDD-1#PBF

LTC3588IDD-1#TRPBF

LFKY

10-Lead (3mm × 3mm) Plastic DFN–40°C to 125°C

LTC3588EMSE-1#PBF

LTC3588EMSE-1#TRPBFLTFKX

10-Lead Plastic MSOP

–40°C to 85°C

LTC3588IMSE-1#PBF

LTC3588IMSE-1#TRPBFLTFKX

10-Lead Plastic MSOP

–40°C to 125°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/This product is only offered in trays. For more information go to: http://www.linear.com/packaging/

35881f2

LTC3588-1
ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating
junction temperature range, otherwise speciﬁcations are at TJ = 25°C. VIN = 5.5V unless otherwise speciﬁed.

SYMBOLPARAMETERCONDITIONS

VIN

Input Voltage Range

Low Impedance Source on VIN

IVIN

VIN Quiescent Current
UVLO
Buck Enabled, Sleeping
Buck Enabled, Sleeping
Buck Enabled, Not Sleeping

VIN = 2.5V, Not PGOOD
VIN = 4.5V
VIN = 18V
ISW = 0A (Note 4)

VUVLO

VIN Undervoltage Lockout Threshold

MIN

MAX

UNITS

18.0

V

450
950
1.7
150

700
1500
2.5
250

nA
nA
μA
μA

VIN Rising
1.8V Output Selected; D1 = 0, D0 = 0
2.5V Output Selected; D1 = 0, D0 = 1
3.3V Output Selected; D1 = 1, D0 = 0
3.6V Output Selected; D1 = 1, D0 = 1

l
l
l
l

3.77
3.77
4.73
4.73

4.04
4.04
5.05
5.05

4.30
4.30
5.37
5.37

V
V
V
V

VIN Falling
1.8V Output Selected; D1 = 0, D0 = 0
2.5V Output Selected; D1 = 0, D0 = 1
3.3V Output Selected; D1 = 1, D0 = 0
3.6V Output Selected; D1 = 1, D0 = 1

l
l
l
l

2.66
2.66
3.42
3.75

2.87
2.87
3.67
4.02

3.08
3.08
3.91
4.28

V
V
V
V

20.0

21.0

V

VSHUNT

VIN Shunt Regulator Voltage

IVIN = 1mA

19.0

ISHUNT

Maximum Protective Shunt Current

1ms Duration

25

Internal Bridge Rectiﬁer Loss(|VPZ1 – VPZ2| – VIN)IBRIDGE = 10μA

350Internal Bridge Rectiﬁer Reverse
Leakage Current

VREVERSE = 18VInternal Bridge Rectiﬁer Reverse
Breakdown Voltage

IREVERSE = 1μA

Regulated Output Voltage

1.8V Output Selected
Sleep Threshold
Wake-Up Threshold
2.5V Output Selected
Sleep Threshold
Wake-Up Threshold
3.3V Output Selected
Sleep Threshold
Wake-Up Threshold
3.6V Output Selected
Sleep Threshold
Wake-Up Threshold

VOUT

TYP

l

PGOOD Falling Threshold

As a Percentage of the Selected VOUT

IVOUT

Output Quiescent Current

VOUT = 3.6V

mA
400

450

mV

20

nA

VSHUNT

30

V

l
l

1.812
1.788

1.890

1.710

V
V

l
l

2.512
2.488

2.575

2.425

V
V

l
l

3.312
3.288

3.399

3.201

V
V

l
l

3.612
3.588

3.708

3.492

V
V

83

92

%

89

150

nA

260

350

mA

IPEAK

Buck Peak Switch Current

200

ILOAD

Available Buck Output Current

100

RP

Buck PMOS Switch On-Resistance

1.1

Ω

RN

Buck NMOS Switch On-Resistance

1.3

Ω

Max Buck Duty Cyclel100

VIH(D0, D1)

D0/D1 Input High Voltagel1.2

VIL(D0, D1)

D0/D1 Input Low Voltagel

IIH(D0, D1)
IIL(D0, D1)

mA

%
V
0.4

V

D0/D1 Input High Current

10nA

D0/D1 Input Low Current

10nA35881f3

LTC3588-1
ELECTRICAL CHARACTERISTICS
Note that the maximum ambient temperature is determined by speciﬁc
operating conditions in conjunction with board layout, the rated package
thermal resistance and other environmental factors.
Note 3: TJ is calculated from the ambient TA and power dissipation PD
according to the following formula: TJ = TA + (PD • θJA).
Note 4: Dynamic supply current is higher due to gate charge being

Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3588E-1 is guaranteed to meet performance speciﬁcations
from 0°C to 85°C. Speciﬁcations over the –40°C to 85°C operating
junction temperature range are assured by design, characterization, andcorrelation with statistical process controls. The LTC3588I-1 is guaranteed
over the full –40°C to 125°C operating junction temperature range.

TYPICAL PERFORMANCE CHARACTERISTICS
IVIN in UVLO vs VIN

IVIN in Sleep vs VIN
2400

D1 = D0 = 1

900

600
–40°C

500

85°C

1800

25°C
IVIN (nA)

400

1600
25°C

1400
1200

300

1000

200

800

–40°C

400
0

1

2

3
VIN (V)

4

5

6

2

4

6

8

10 12
VIN (V)14

D1 = D0 = 1
4.0

3.6
3.4

Total Bridge Rectiﬁer Dropvs Bridge Current

21.0

1800

20.8

1600

20.6

1400

20.2
20.0

ISHUNT = 25mA
ISHUNT = 1mA

19.8

D1 = D0 = 0
5 25 45 65 85 105 125
TEMPERATURE (°C)
35881 G04

–40°C

1200
85°C

1000
800

19.4

400

19.2

200

19.0
–55 –35 –15|VPZ1 – VPZ2| – VIN

25°C

600

19.6

3.2

5 25 45 65 85 105 125
TEMPERATURE (°C)
35881 G03

20.4

D1 = 1, D0 = 0
VSHUNT (V)UVLO FALLING (V)3.8–55 –35 –15

18

VSHUNT vs Temperature

4.2

2.8
–55 –35 –15

1635881 G02

UVLO Falling vs Temperature

3.0

4.4

D1 = D0 = 035881 G01

3.8

4.6

4.0

600

100

4.8

4.2

VBRIDGE (mV)

IVIN (nA)

D1 = D0 = 1
5.0

2000

800

0

D1 = D0 = 0

2200

85°C

700

UVLO Rising vs Temperature
5.2

UVLO RISING (V)1000

5 25 45 65 85 105 125
TEMPERATURE (°C)
35881 G05

0

1μ

10μ

100μ
1m
BRIDGE CURRENT (A)10m
35881 G06

35881f4

LTC3588-1
TYPICAL PERFORMANCE CHARACTERISTICS
Bridge Leakage vs Temperature

16

1.6

14

1.4

12

1.2

10

0.8

6

0.6

4

0.4

2

0.2
–10

35
80
125
TEMPERATURE (°C)

0170

SLEEP THRESHOLD
1.80
WAKE-UP THRESHOLD

1.0

8

0
–55

1.8V Output vs Temperature
1.85

4VP-P APPLIED TO PZ1/PZ2 INPUT
1.8 MEASURED IN UVLO

VIN = 18V, LEAKAGE AT PZ1 OR PZ2

VIN (V)

BRIDGE LEAKAGE (nA)18

Bridge Frequency Response
2.0

VOUT (V)20

PGOOD FALLING

10

100

1k

10k 100k 1M
FREQUENCY (Hz)1.60
–55 –35 –15

10M 100M

2.5V Output vs Temperature

35881 G09

3.6V Output vs Temperature

3.3V Output vs Temperature
3.35

3.65
SLEEP THRESHOLDSLEEP THRESHOLDSLEEP THRESHOLD

3.60

3.30

2.50

WAKE-UP THRESHOLD

WAKE-UP THRESHOLD

WAKE-UP THRESHOLD

3.55

3.25
3.20

VOUT (V)VOUT (V)VOUT (V)

2.45
2.40

5 25 45 65 85 105 125
TEMPERATURE (°C)

35881 G08

2.55

3.15

3.50
3.45
3.40

2.35

3.10
PGOOD FALLING

2.30

2.25
–55 –35 –15

3.35

3.05

3.00
–55 –35 –15

5 25 45 65 85 105 125
TEMPERATURE (°C)

PGOOD FALLINGPGOOD FALLING

3.30
3.25
–55 –35 –15

5 25 45 65 85 105 125
TEMPERATURE (°C)

VOUT Load Regulation

35881 G12VOUT Line Regulation
2.56
2.54

2.52

2.52
VOUT (V)

2.54

IVOUT vs Temperature120

L = 10μH, ILOAD = 100mA, D1 = 0, D0 = 1

110

90

2.50

2.48

2.48

2.46

2.46

VOUT = 3.6V

100

IVOUT (nA)

VIN = 5V, L = 10μH, D1 = 0, D0 = 1

2.50

5 25 45 65 85 105 125
TEMPERATURE (°C)

35881 G11

35881 G10VOUT (V)

1.70

1.65

35881 G07

2.56

1.75

80

VOUT = 3.3V

70
60
50
40

VOUT = 2.5V
VOUT = 1.8V

30
2.44

1μ

10μ

100μ
1m
10m
LOAD CURRENT (A)100m
35881 G13

2.44

4

6

8

10
12
VIN (V)

14

16

18

35881 G14

20
–55 –35 –15

5 25 45 65 85 105 125
TEMPERATURE (°C)
35881 G15

35881f5

LTC3588-1
TYPICAL PERFORMANCE CHARACTERISTICSRDS(ON) of PMOS/NMOS
vs Temperature

IPEAK vs Temperature

Operating Waveforms

2.0

300

OUTPUT
VOLTAGE
50mV/DIV
AC-COUPLED

290
1.8

280

NMOS
1.6
RDS(ON) (Ω)

IPEAK (mA)

270
260
250
240

SWITCHVOLTAGE
2V/DIV

1.4
PMOS

0V
INDUCTORCURRENT
200mA/DIV
0mA

1.2

230
220

1.0

210
200
–55 –35 –15

0.8–55 –35 –15

5 25 45 65 85 105 125
TEMPERATURE (°C)

5 25 45 65 85 105 125
TEMPERATURE (°C)
35881 G17

35881 G16

Efﬁciency vs VIN for
ILOAD = 100mA, L = 10μH

Efﬁciency vs ILOAD, L = 10μH
90

VIN = 5V

80
EFFICIENCY (%)

EFFICIENCY (%)

70
60
50
40
30

VOUT = 3.6V
VOUT = 3.3V
VOUT = 2.5V
VOUT = 1.8V

20
10
0

1μ

10μ

100μ
1m
10m
LOAD CURRENT (A)

100

95

90

85

80

75

70
60
VOUT = 3.6V
VOUT = 3.3V
VOUT = 2.5V
VOUT = 1.8V

50
40

100m

2

4

6

8

10 12
VIN (V)

14

EFFICIENCY (%)

EFFICIENCY (%)

80
70
60
50
40
30
VOUT = 3.6V
VOUT = 3.3V
VOUT = 2.5V
VOUT = 1.8V

10
0

1μ

10μ

100μ
1m
10m
LOAD CURRENT (A)100m
35881 G22

ILOAD = 100mA
ILOAD = 1mA
ILOAD = 100μA
ILOAD = 50μA
ILOAD = 10μA

45
35

18

4

6

8

10
12
VIN (V)

14

95

90

85

80

75

70
60

40

VOUT = 3.6V
VOUT = 3.3V
VOUT = 2.5V
VOUT = 1.8V
2

4

6

8

10 12
VIN (V)14

18

Efﬁciency vs VIN for
VOUT = 3.3V, L = 100μH

100

50

16

35881 G21

EFFICIENCY (%)

VIN = 5V

20

55

Efﬁciency vs VIN for
ILOAD = 100mA, L = 100μH

Efﬁciency vs ILOAD, L = 100μH
90

16

65

35881 G20

35881 G19100

Efﬁciency vs VIN for
VOUT = 3.3V, L = 10μH

EFFICIENCY (%)

100

35881 G18

5μs/DIV
VIN = 5V, VOUT = 3.3V
ILOAD = 1mA
L = 10μH, COUT = 47μF

161835881 G23

65
55

ILOAD = 100mA
ILOAD = 100μA
ILOAD = 50μA
ILOAD = 30μA
ILOAD = 10μA

45
35

4

6

8

10
12
VIN (V)

14

16

18

35881 G24

35881f6

LTC3588-1
PIN FUNCTIONSPZ1 (Pin 1): Input connection for piezoelectric element orother AC source (used in conjunction with PZ2).
PZ2 (Pin 2): Input connection for piezoelectric element orother AC source (used in conjunction with PZ1).
CAP (Pin 3): Internal rail referenced to VIN to serve as gate
drive for buck PMOS switch. A 1μF capacitor should beconnected between CAP and VIN. This pin is not intended
for use as an external system rail.
VIN (Pin 4): Rectiﬁed Input Voltage. A capacitor on thispin serves as an energy reservoir and input supply for thebuck regulator. The VIN voltage is internally clamped to a
maximum of 20V (typical).
SW (Pin 5): Switch Pin for the Buck Switching Regulator.
A 10μH or larger inductor should be connected from SW
to VOUT.
VOUT (Pin 6): Sense pin used to monitor the output voltage and adjust it through internal feedback.

VIN2 (Pin 7): Internal low voltage rail to serve as gate drivefor buck NMOS switch. Also serves as a logic high rail for
output voltage select bits D0 and D1. A 4.7μF capacitor
should be connected from VIN2 to GND. This pin is notintended for use as an external system rail.
D1 (Pin 8): Output Voltage Select Bit. D1 should be tiedhigh to VIN2 or low to GND to select desired VOUT (seeTable 1).
D0 (Pin 9): Output Voltage Select Bit. D0 should be tiedhigh to VIN2 or low to GND to select desired VOUT (seeTable 1).
PGOOD (Pin 10): Power good output is logic high when
VOUT is above 92% of the target value. The logic high isreferenced to the VOUT rail.
GND (Exposed Pad Pin 11): Ground. The Exposed Pad
should be connected to a continuous ground plane on thesecond layer of the printed circuit board by several vias
directly under the LTC3588-1.

35881f7

LTC3588-1
BLOCK DIAGRAM
VIN 4
20V

INTERNAL RAIL
GENERATION
3

CAP

5

SW

7

VIN2

PZ1 1

PZ2 2
BUCK
CONTROL

UVLO

11 GNDSLEEP
BANDGAPREFERENCE
8, 9
D1, D0

6

VOUT

2
PGOOD
COMPARATOR

10 PGOOD

35881 BD35881f8

LTC3588-1
OPERATION

Internal Bridge Rectiﬁer
The LTC3588-1 has an internal full-wave bridge rectiﬁer
accessible via the differential PZ1 and PZ2 inputs that
rectiﬁes AC inputs such as those from a piezoelectricelement. The rectiﬁed output is stored on a capacitor at
the VIN pin and can be used as an energy reservoir for thebuck converter. The low-loss bridge rectiﬁer has a total
drop of about 400mV with typical piezo generated currents(~10μA). The bridge is capable of carrying up to 50mA.
One side of the bridge can be operated as a single-ended
DC input. PZ1 and PZ2 should never be shorted together
when the bridge is in use.

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 output voltage select bits D0
and D1. The VIN2 rail is regulated at 4.8V above GND while
the CAP rail is regulated at 4.8V below VIN. These are notintended to be used as external rails. Bypass capacitors
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.
18
16
14
VOLTAGE (V)The LTC3588-1 is an ultralow quiescent current power
supply designed speciﬁcally for energy harvesting and/or
low current step-down applications. The part is designed tointerface directly to a piezoelectric or alternative A/C powersource, rectify a voltage waveform and store harvested
energy on an external capacitor, bleed off any excess power
via an internal shunt regulator, and maintain a regulated
output voltage by means of a nanopower high efﬁciency
synchronous buck regulator.

108
6

When the voltage on VIN rises above the UVLO risingthreshold the buck converter is enabled and charge istransferred from the input capacitor to the output capacitor. A wide (~1V) UVLO hysteresis window is employedwith a lower threshold approximately 300mV above theselected regulated output voltage to prevent short cycling
during buck power-up. When the input capacitor voltage
is depleted below the UVLO falling threshold the buckconverter is disabled. 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.

VIN2

4
CAP

2
0

Undervoltage Lockout (UVLO)

VIN

12

0

5

10

15

VIN (V)35881 F01

Figure 1. Ideal VIN, VIN2 and CAP RelationshipBuck 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 theinductor 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, VOUT,
and the inductor value. If the input voltage falls below the35881f9

LTC3588-1
OPERATION

When the sleep comparator signals that the output hasreached the sleep threshold the buck converter may bein the middle of a cycle with current still ﬂowing throughthe inductor. Normally both synchronous switches would
turn off and the current in the inductor would freewheel
to zero through the NMOS body diode. The LTC3588-1
keeps the NMOS switch on during this time to prevent the
conduction loss that would occur in the diode if the NMOS
were off. If the PMOS is on when the sleep comparator
trips the NMOS will turn on immediately in order to ramp
down the current. If the NMOS is on it will be kept on until
the current reaches zero.
Though the quiescent current when the buck is switchingis much greater than the sleep quiescent current, it is stilla small percentage of the average inductor current which
results in high efﬁciency over most load conditions. The
buck operates only when sufﬁcient energy has been accumulated in the input capacitor and the length of time theconverter needs to transfer energy to the output is muchless than the time it takes to accumulate energy. Thus, thebuck operating quiescent current is averaged over a long
period of time so that the total average quiescent current
is low. This feature accommodates sources that harvest
small amounts of ambient energy.
Four selectable voltages are available by tying the output
select bits, D0 and D1, to GND or VIN2. Table 1 shows
the four D0/D1 codes and their corresponding output
voltages.

Table 1. Output Voltage Selection
D1

D0

VOUT

0

0

1.8V

44nA

0

1

2.5V

62nA

1

0

3.3V

81nA

1

1

3.6V

89nA

VOUT QUIESCENT CURRENT (IVOUT)

The internal feedback network draws a small amount of
current from VOUT as listed in Table 1.
Power Good Comparator
A power good comparator produces a logic high referenced
to VOUT on the PGOOD pin the ﬁrst time the converter
reaches the sleep threshold of the programmed VOUT,
signaling that the output is in regulation. The PGOOD pin
will remain high until VOUT falls to 92% of the desired
regulation voltage. Several sleep cycles may occur during
this time. Additionally, if PGOOD is high and VIN falls below
the UVLO falling threshold, PGOOD will remain high until
VOUT falls to 92% of the desired regulation point. This
allows output energy to be used even if the input is lost.
Figure 2 shows the behavior for VOUT = 3.6V and no load.
At t = 75s VIN becomes high impedance and is discharged
by the quiescent current of the LTC3588-1 and throughservicing VOUT which is discharged by its own leakage
current. VIN crosses UVLO falling but PGOOD remains highuntil VOUT decreases to 92% of the desired regulation point.
The PGOOD pin is designed to drive a microprocessor orother chip I/O and is not intended to drive higher current
loads such as an LED.
6

CVIN = CVOUT = 100μF

5VOLTAGE (V)UVLO falling threshold before the output voltage reaches
regulation, the buck converter will shut off and will not
be turned on until the input voltage again rises above the
UVLO rising threshold. During this time the output voltage
will be loaded by less than 100nA. When the buck brings
the output voltage into regulation the converter enters alow quiescent current sleep state that monitors the output
voltage with a sleep comparator. During this operating modeload current is provided by the buck output capacitor. Whenthe output voltage falls below the regulation point the buckregulator wakes up and the cycle repeats. This hysteretic
method of providing a regulated output reduces losses
associated with FET switching and maintains an output
at light loads. The buck delivers a minimum of 100mA of
average load current when it is switching.

VIN
VIN = UVLO FALLING

4

VOUT
3
2
PGOOD
1
0

0

100

200

300

TIME (s)35881 F02

Figure 2. PGOOD Operation During Transition to UVLO
35881f10

LTC3588-1
OPERATION
The D0/D1 inputs can be switched while in regulation asshown in Figure 3. If VOUT is programmed to a voltage witha PGOOD falling threshold above the old VOUT, PGOOD willtransition low until the new regulation point is reached.
When VOUT is programmed to a lower voltage, PGOOD
will remain high through the transition.
5

COUT = 100μF, ILOAD = 100mA
D1=D0=0

VOUT VOLTAGE (V)4

D1=D0=1

D1=D0=0

3

VOUT

2

1

0

PGOOD = LOGIC1

0

2

4

6

Energy Storage
Harvested energy can be stored on the input capacitor
or the output capacitor. The wide input range takes advantage of the fact that energy storage on a capacitor is
proportional to the square of the capacitor voltage. Afterthe output voltage is brought into regulation any excessenergy is stored on the input capacitor and its voltage
increases. When a load exists at the output the buck can
efﬁciently transfer energy stored at a high voltage to theregulated output. While energy storage at the input utilizes
the high voltage at the input, the load current is limited
to what the buck converter can supply. If larger loads
need to be serviced the output capacitor can be sized tosupport a larger current for some duration. For example,
a current burst could begin when PGOOD goes high andwould continuously deplete the output capacitor until
PGOOD went low.

8 10 12 14 16 18 20
TIME (ms)35881 F03

Figure 3. PGOOD Operation During D0/D1 Transition

35881f11

LTC3588-1
APPLICATIONS INFORMATION
Introduction
The LTC3588-1 harvests ambient vibrational energy
through a piezoelectric element in its primary application.
Common piezoelectric elements are PZT (lead zirconate
titanate) ceramics, PVDF (polyvinylidene ﬂuoride) polymers, or other composites. Ceramic piezoelectric elements
exhibit a piezoelectric effect when the crystal structureof the ceramic is compressed and internal dipole movement produces a voltage. Polymer elements comprisedof long-chain molecules produce a voltage when ﬂexed
as molecules repel each other. Ceramics are often used
under direct pressure while a polymer can be ﬂexed more
readily. A wide range of piezoelectric elements are available and produce a variety of open-circuit voltages andshort-circuit currents. Typically the open-circuit voltage
and short-circuit currents increase with available vibrationalenergy as shown in Figure 4. Piezoelectric elements canbe placed in series or in parallel to achieve desired opencircuit voltages.
12

PIEZO VOLTAGE (V)9
INCREASING
VIBRATION ENERGY
6

3

0

0

10
20
PIEZO CURRENT (μA)

30

The LTC3588-1 is well-suited to a piezoelectric energy
harvesting application. The 20V input protective shunt
can accommodate a variety of piezoelectric elements. The
low quiescent current of the LTC3588-1 enables efﬁcientenergy accumulation from piezoelectric elements which
can have short-circuit currents on the order of tens of
microamps. Piezoelectric elements can be obtained frommanufacturers listed in Table 2.
Table 2. Piezoelectric Element Manufacturers
Advanced Cerametrics

www.advancedcerametrics.com

Piezo Systems

www.piezo.com

Measurement Specialties

www.meas-spec.com

PI (Physik Instrumente)www.pi-usa.us

MIDE Technology Corporationwww.mide.com

Morgan Technical Ceramics

www.morganelectroceramics.com

The LTC3588-1 will gather energy and convert it to a useable output voltage to power microprocessors, wirelesssensors, and wireless transmission components. Such awireless sensor application may require much more peak
power than a piezoelectric element can produce. However,the LTC3588-1 accumulates energy over a long period oftime to enable efﬁcient use for short power bursts. For
continuous operation, these bursts must occur with a low
duty cycle such that the total output energy during the burst
does not exceed the average source power integrated overan energy accumulation cycle. For piezoelectric inputs thetime between cycles could be minutes, hours, or longer
depending on the selected capacitor values and the natureof the vibration source.

35881 F04

Figure 4. Typical Piezoelectric Load Linesfor Piezo Systems T220-A4-503X

35881f12

LTC3588-1
APPLICATIONS INFORMATION

1μF
6V
10μF
25V
4.7μF
6V

PZ1

PZ2

VIN

PGOOD

CAP LTC3588-1

SW

VIN2

VOUT

D1
D0

TX

EN
10μH

3.3V

MICROPROCESSOR
CORE

GND

47μF
6V

OUTPUT
VOLTAGE
20mV/DIV
AC-COUPLEDLOAD
CURRENT
25mA/DIV
5mA

GND
35881 F05a

35881 F05b

250μs/DIV
VIN = 5V
L = 10μH, COUT = 47μF
LOAD STEP BETWEEN 5mA and 55mA

Figure 5. 3.3V Piezoelectric Energy Harvester Powering a Microprocessor
with a Wireless Transmitter and 50mA Load Step Response

PGOOD Signal
The PGOOD signal can be used to enable a sleeping
microprocessor or other circuitry when VOUT reaches
regulation, as shown in Figure 5. Typically VIN will besomewhere between the UVLO thresholds at this timeand a load could only be supported by the output capacitor. Alternatively, waiting a period of time after PGOOD
goes high would let the input capacitor accumulate moreenergy allowing load current to be maintained longer as
the buck efﬁciently transfers that energy to the output.
While active, a microprocessor may draw a small loadwhen operating sensors, and then draw a large load totransmit data. Figure 5 shows the LTC3588-1 respondingsmoothly to such a load step.
Input and Output Capacitor Selection
The input and output capacitors should be selected basedon the energy needs and load requirements of the application. In every case the VIN capacitor should be rated
to withstand the highest voltage ever present at VIN.
For 100mA or smaller loads, storing energy at the input
takes advantage of the high voltage input since the buckcan deliver 100mA average load current efﬁciently to the
output. The input capacitor should then be sized to store
enough energy to provide output power for the length oftime required. This may involve using a large capacitor,

letting VIN charge to a high voltage, or both. Enough energy
should be stored on the input so that the buck does notreach the UVLO falling threshold which would halt energy
transfer to the output. In general:(

1
PLOAD tLOAD = ηCIN VIN 2 − VUVLOFALLING 22
VUVLOFALLING ≤ VIN ≤ VSHUNT)The above equation can be used to size the input capacitor to meet the power requirements of the output for thedesired duration. Here η is the average efﬁciency of thebuck converter over the input range and VIN is the input
voltage when the buck begins to switch. This equation
may overestimate the input capacitor necessary since load
current can deplete the output capacitor all the way to thelower PGOOD threshold. It also assumes that the input
source charging has a negligible effect during this time.
The duration for which the regulator sleeps depends on
the load current and the size of the output capacitor. The
sleep time decreases as the load current increases and/or
as the output capacitor decreases. The DC sleep hysteresis
window is ±12mV around the programmed output voltage. Ideally this means that the sleep time is determinedby the following equation:t SLEEP = COUT

24mV
ILOAD
35881f13

LTC3588-1
APPLICATIONS INFORMATIONThis 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 withthe load current may result in the VOUT voltage slewing
past the ±12mV thresholds. This will lengthen the sleep
time and increase VOUT ripple. A capacitor less than 10μF
is not recommended as VOUT ripple could increase to an
undesirable level.
If transient load currents above 100mA are required then alarger 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
VOUT:
I
−I
COUT = ( VOUT+ − VOUT– ) LOAD BUCKtLOADHere VOUT+ is the value of VOUT when PGOOD goes highand VOUT– is the desired lower limit of VOUT. IBUCK is theaverage current being delivered from the buck converter,
typically IPEAK /2.
A standard surface mount ceramic capacitor can be used
for COUT, though some applications may be better suited
to a low leakage aluminum electrolytic capacitor or asupercapacitor. These capacitors can be obtained frommanufacturers such as Vishay, Illinois Capacitor, AVX,
or CAP-XX.
Inductor
The buck is optimized to work with an inductor in the rangeof 10μH to 22μH, although inductor values outside thisrange may yield beneﬁts in some applications. For typicalapplications, 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 theinductor can have an impact on efﬁciency as it is a sourceof loss. Tradeoffs between price, size, and DCR should be
evaluated. Table 3 lists several inductors that work wellwith the LTC3588-1.
Table 3. Recommended Inductors for LTC3588-1
INDUCTOR
TYPE

L
(μH)

MAX
IDC
(mA)

MAX
DCR
(Ω)

SIZE in mm(L × W × H)

MANUFACTURER

CDRH2D18/LDNP

10

430

0.180

3×3×2

Sumida107AS-100M

10

650

0.145

2.8 × 3 × 1.8

Toko

EPL3015-103ML

10

350

0.301

2.8 × 3 × 1.5

Coilcraft

MLP3225s100L

10

1000

0.130 3.2 × 2.5 × 1.0

TDK

XLP2010-163ML

10

490

0.611 2.0 × 1.9 × 1.0

Coilcraft

SLF7045T

100

500

0.250 7.0 × 7.0 × 4.5

TDK

VIN2 and CAP Capacitors
A 1μF capacitor should be connected between VIN and
CAP and a 4.7μF capacitor should be connected between
VIN2 and GND. These capacitors hold up the internal rails
during buck switching and compensate the internal rail
generation circuits. In applications where the input sourceis limited to less than 6V, the CAP pin can be tied to GND
and the VIN2 pin can be tied to VIN as shown in Figure 6.
An optional 5.6V Zener diode can be connected to VIN toclamp VIN in this scenario. The leakage of the Zener diodebelow 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 VIN2 and
CAP, saving components and allowing a lower voltage
rating for the single VIN capacitor.
PIEZO SYSTEMS T220-A4-503X

PZ1

PZ2

VIN

PGOOD

VIN2
5.6V
(OPTIONAL)

10μF
6V

PGOOD
10μH

LTC3588-1

CAP

SW

D1

VOUT

VOUT
1.8V
10μF
6V

D0
GND
35881 F06

Figure 6. Smallest Solution Size 1.8V Low Voltage Input
Piezoelectric Power Supply
35881f14

LTC3588-1
APPLICATIONS INFORMATION
A piezo powered LTC3588-1 can also be used in concert
with a battery connected to VIN to supplement the systemif ambient vibrational energy ceases as shown in Figure 8.
A blocking diode placed in series with the battery to VIN
prevents reverse current in the battery if the piezo source
charges VIN past the battery voltage. A 9V battery is shown,
but any stack of batteries of a given chemistry can be used
as long as the battery stack voltage does not exceed 18V.
In this setup the presence of the piezo energy harvester
can greatly increase the life of the battery. If the piezo
source is removed the LTC3588-1 can serve as a standalone nanopower buck converter. In this case the bridge
is unused and the blocking diode is unnecessary.

Additional Applications with Piezo Inputs
The versatile LTC3588-1 can be used in a variety of conﬁgurations. Figure 7 shows a single piezo source powering
two LTC3588-1s simultaneously, providing capability for
multiple rail systems. This setup features automatic supply sequencing as the LTC3588-1 with the lower voltage
output (i.e. lower UVLO rising threshold) will come up ﬁrst.
As the piezo provides input power both VIN rails will
initially come up together, but when one output starts
drawing power, only its corresponding VIN will fall as thebridges of each LTC3588-1 provide isolation. Input piezoenergy will then be directed to this lower voltage capacitor
until both VIN rails are again equal. This conﬁguration is
expandable to any number of LTC3588-1s powered by asingle piezo as long as the piezo can support the sum totalof the quiescent currents from each LTC3588-1.

PIEZO SYSTEMS T220-A4-503X

PGOOD1

PZ1

PZ2

PZ1

PZ2

PGOOD

VIN

VIN

PGOOD

10μH
3.6V

1μF
6V

LTC3588-1
SW

CAP

VOUT

VIN2

10μF
6V

10μF
25V

D1

PGOOD210μH

LTC3588-1

10μF
25V

4.7μF
6V

D0

GND

1μF
6V
CAP

SW

VIN2

VOUT

1.8V
10μF
6V

D1

4.7μF
6V

D0

GND
35881 F07

Figure 7. Dual Rail Power Supply with Single Piezo andAutomatic Supply Sequencing

PIEZO SYSTEMS T220-A4-503X

IR05H40CSPTR

PZ1

PZ2

VIN

PGOOD

1μF
6V
9V
BATTERY

100μF
16V
4.7μF
6V

10μH

LTC3588-1
CAP

SW

VIN2

VOUT

D1

PZ1

D0

GND

PGOOD
VOUT
3.3V
47μF
6V

PZ2

35881 F08

Figure 8. Piezo Energy Harvester with Battery Backup
35881f15

LTC3588-1
APPLICATIONS INFORMATIONDANGER! HIGH VOLTAGE!
DANGEROUS AND LETHAL POTENTIALS ARE PRESENT IN OFFLINE CIRCUITS!
150k

150k

120VAC
60Hz 150k

150k

BEFORE PROCEEDING ANY FURTHER, THE READER IS WARNED THATCAUTION MUST BE USED IN THE CONSTRUCTION, TESTING AND USE OFOFFLINE CIRCUITS. EXTREME CAUTION MUST BE USED IN WORKING WITH
PZ1

PZ2

VIN

PGOOD

1μF
6V
10μF
25V
4.7μF
6V

AND MAKING CONNECTIONS TO THESE CIRCUITS. REPEAT: OFFLINEPGOODCIRCUITS CONTAIN DANGEROUS, AC LINE-CONNECTED HIGH VOLTAGE
POTENTIALS. USE CAUTION. ALL TESTING PERFORMED ON AN OFFLINE

10μH

LTC3588-1
CAP

SW

VIN2

VOUT

D1
D0

VOUT
3.6V

CIRCUIT MUST BE DONE WITH AN ISOLATION TRANSFORMER CONNECTED

100μF
6V

CONSTRUCTORS OF OFFLINE CIRCUITS MUST OBSERVE THIS PRECAUTIONGND

BETWEEN THE OFFLINE CIRCUIT’S INPUT AND THE AC LINE. USERS AND
WHEN CONNECTING TEST EQUIPMENT TO THE CIRCUIT TO AVOID ELECTRICSHOCK. REPEAT: AN ISOLATION TRANSFORMER MUST BE CONNECTED
BETWEEN THE CIRCUIT INPUT AND THE AC LINE IF ANY TEST EQUIPMENT IS

35881 F09

TO BE CONNECTED.

Figure 9. AC Line Powered 3.6V Buck Regulator with
Large Output Capacitor to Support Heavy Loads

COPPER PANEL(12" s 24")PANELS ARE PLACED 6"
FROM 2' s 4' FLUORESCENT
LIGHT FIXTURES
PZ1

PZ2

VIN

PGOOD

1μF
6V
10μF
25V
4.7μF
6V

COPPER PANEL(12" s 24")

PGOOD
10μH

LTC3588-1
CAP

SW

VIN2

VOUT

3.3V
10μF
6V

D1
D0

GND
35881 F10

Figure 10. Electric Field Energy Harvester

Alternate Power Sources
The LTC3588-1 is not limited to use with piezoelectric elements but can accommodate a wide variety of input sources
depending on the type of ambient energy available. Figure 9shows the LTC3588-1 internal bridge rectiﬁer connectedto the AC line in series with four 150k current limiting
resistors. This is a high voltage application and minimum
spacing between the line, neutral, and any high voltage
components should be maintained per the applicable UL
speciﬁcation. For general off-line applications refer to UL
regulation 1012.
Figure 10 shows an application where copper panels areplaced near a standard ﬂuorescent room light to capacitively

harvest energy from the electric ﬁeld around the light.
The frequency of the emission will be 120Hz for magnetic
ballasts but could be higher if the light uses electronicballast. The LTC3588-1 bridge rectiﬁer can handle a wide
range of input frequencies.
The LTC3588-1 can also be conﬁgured for use with DC
sources such as a solar panel or thermal couple as shownin Figures 11 and 12 by connecting them to one of the
PZ1/PZ2 inputs. Connecting the two sources in this way
prevents reverse current from ﬂowing in each element.
Current limiting resistors should be used to protect thePZ1 or PZ2 pins. This can be combined with a battery
backup connected to VIN with a blocking diode.
35881f16

LTC3588-1
APPLICATIONS INFORMATION
300Ω
PZ1

PZ2

VIN

PGOOD

IR05H4OCSPTR

+
–

1μF
6V

5V TO 16V
SOLAR PANEL
9V
BATTERY

100μF
25V
4.7μF
6V

LTC3588-1

PGOOD
10μH

CAP

SW

VIN2

VOUT

VOUT
2.5V

+

D0
D1

10μF
6V

GND

3F
2.7V
NESS SUPER CAPACITORESHSR-0003CO-002R7

35881 F11

Figure 11. 5V to 16V Solar-Powered 2.5V Supply with Supercapacitor for
Increased Output Energy Storage and Battery Backup

RS, 5.2Ω

100Ω

PG-1 THERMAL
GENERATOR
P/N G1-1.0-127-1.27(TELLUREX)

1μF
6V
5.4V

1μF
16V
4.7μF
6V

PZ1

PZ2

VIN

PGOOD
LTC3588-1

PGOOD
10μH

CAP

SW

VIN2

VOUT

VOUT
2.5V
47μF
6V

D0
D1

GND
35881 F12

Figure 12. Thermoelectric Energy Harvester

35881f17

LTC3588-1
PACKAGE DESCRIPTIONDD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)

R = 0.115
TYP
6

10

5

1

0.38 ± 0.10

0.675 ±0.05

3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)

3.00 ±0.10(4 SIDES)
PACKAGEOUTLINE

PIN 1
TOP MARK(SEE NOTE 6)
0.200 REF

0.25 ± 0.05

1.65 ± 0.10
(2 SIDES)

0.50
BSC
2.38 ±0.05(2 SIDES)(DD) DFN 1103

0.25 ± 0.05
0.50 BSC

0.75 ±0.05

0.00 – 0.05

2.38 ±0.10(2 SIDES)
BOTTOM VIEW—EXPOSED PADRECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE

35881f18

LTC3588-1
PACKAGE DESCRIPTIONMS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661 Rev E)

BOTTOM VIEW OFEXPOSED PAD OPTION

2.794 p 0.102(.110 p .004)

5.23(.206)
MIN

0.889 p 0.127(.035 p .005)

1

2.06 p 0.102(.081 p .004)
1.83 p 0.102(.072 p .004)

2.083 p 0.102 3.20 – 3.45(.082 p .004) (.126 – .136)

10

0.50
0.305 p 0.038(.0197)(.0120 p .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT

3.00 p 0.102(.118 p .004)(NOTE 3)10 9 8 7 6

3.00 p 0.102(.118 p .004)(NOTE 4)4.90 p 0.152(.193 p .006)
0.254(.010)DETAIL “A”
0o – 6o TYP
1 2 3 4 5

GAUGE PLANE
0.53 p 0.152(.021 p .006)
DETAIL “A”
0.18(.007)

0.497 p 0.076(.0196 p .003)
REF

SEATING
PLANE

0.86(.034)
REF

1.10(.043)
MAX

0.17 – 0.27(.007 – .011)
TYP

0.50
(.0197)BSC

0.1016 p 0.0508(.004 p .002)
MSOP (MSE) 0307 REV B

NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

35881fInformation furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

19

LTC3588-1
TYPICAL APPLICATION
Peak-to-Peak Output Ripple vs COUT1

Piezoelectric 3.3V Power Supply with LDO
Post Regulator for Reduced Output Ripple

47μF
25V
4.7μF
6V

PZ2

VIN

PGOOD

SHDN
10μH

CAP LTC3588-1

SW

VIN2

VOUT

VOUT1
3.6V

D1
D0

GND

LT3009-3.3
IN

OUT
GND

COUT1
10μF
6V

VOUT2
3.3V
20mA
COUT2
1μF
6V

VOUT RIPPLE PEAK-TO-PEAK (mV)

1μF
6V

PZ1

120
100

VOUT1 (LTC3588-1)

80
60
40

VOUT2 (LT3009-3.3)

20035881 TA02a

COUT2 = 1μF

10100
COUT1 (μF)
35881 TA02b

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35881f

20 Linear Technology Corporation

LT 0110 • PRINTED IN USA

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