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LTC3588-1 Piezoelectric Energy Harvesting Power Supply FEATURES
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DESCRIPTION
The LTC(R)3588-1 integrates a low-loss full-wave bridge rectifier with a high efficiency buck converter to form a complete energy harvesting solution optimized for high output impedance energy sources such as piezoelectric transducers. An ultralow quiescent current undervoltage lockout (UVLO) mode with a wide hysteresis window allows charge to accumulate on an input capacitor until the buck converter can efficiently transfer a portion of the stored charge to the output. In regulation, the LTC3588-1 enters a sleep state in which both input and output quiescent currents are minimal. The buck converter turns on and off as needed to maintain regulation. Four 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 a higher output current burst. An input protective shunt set at 20V enables greater energy storage for a given amount of input capacitance.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
950nA Input Quiescent Current (Output in Regulation - No Load) 450nA Input Quiescent Current in UVLO 2.7V to 20V Input Operating Range Integrated Low-Loss Full-Wave Bridge Rectifier Up to 100mA of Output Current Selectable Output Voltages of 1.8V, 2.5V, 3.3V, 3.6V High Efficiency Integrated Hysteretic Buck DC/DC Input Protective Shunt - Up to 25mA Pull-Down at VIN 20V Wide Input Undervoltage Lockout (UVLO) Range Available in 10-Lead MSE and 3mm x 3mm DFN Packages
APPLICATIONS
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Piezoelectric Energy Harvesting Electro-Mechanical Energy Harvesting Wireless HVAC Sensors Mobile Asset Tracking Tire Pressure Sensors Battery Replacement for Industrial Sensors Remote Light Switches Standalone Nanopower Buck Regulator
TYPICAL APPLICATION
100mA Piezoelectric Energy Harvesting Power Supply LTC3588-1 3.3V Regulator Start-Up Profile
22 CSTORAGE = 22F COUT = 47F , 20 NO LOAD, IVIN = 2A 18 16 VIN 1F 6V CSTORAGE 25V 4.7F 6V CAP VIN2 GND
35881 TA01
ADVANCED CERAMETRICS PFC-W14 VOLTAGE (V) PZ1 LTC3588-1 PZ2 SW VOUT 2 OUTPUT VOLTAGE SELECT 47F 6V 10H VOUT
14 12 10 8 6 4 2 0 0 200
VIN
PGOOD D0, D1
VOUT PGOOD = LOGIC 1 400 TIME (s) 600
35881 TA01b
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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 125C Storage Temperature Range.......................-65 to 125C Lead Temperature (Soldering, 10 sec) MSE Only .......................................................... 300C
PIN CONFIGURATION
TOP VIEW PZ1 PZ2 CAP VIN SW 1 2 3 4 5 11 GND 10 PGOOD 9 D0 8 D1 7 VIN2 6 VOUT TOP VIEW PZ1 PZ2 CAP VIN SW 1 2 3 4 5 11 GND 10 9 8 7 6 PGOOD D0 D1 VIN2 VOUT
DD PACKAGE 10-LEAD (3mm 3mm) PLASTIC DFN TJMAX = 125C, JA = 43C/W, JC = 7.5C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
MSE PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125C, JA = 45C/W, JC = 10C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC3588EDD-1#PBF LTC3588IDD-1#PBF LTC3588EMSE-1#PBF LTC3588IMSE-1#PBF TAPE AND REEL LTC3588EDD-1#TRPBF LTC3588IDD-1#TRPBF LTC3588EMSE-1#TRPBF LTC3588IMSE-1#TRPBF PART MARKING* LFKY LFKY LTFKX LTFKX PACKAGE DESCRIPTION 10-Lead (3mm x 3mm) Plastic DFN 10-Lead (3mm x 3mm) Plastic DFN 10-Lead Plastic MSOP 10-Lead Plastic MSOP TEMPERATURE RANGE -40C to 85C -40C to 125C -40C to 85C -40C to 125C
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/
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LTC3588-1 ELECTRICAL CHARACTERISTICS
SYMBOL VIN IVIN PARAMETER Input Voltage Range VIN Quiescent Current UVLO Buck Enabled, Sleeping Buck Enabled, Sleeping Buck Enabled, Not Sleeping VIN Undervoltage Lockout Threshold
The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TJ = 25C. VIN = 5.5V unless otherwise specified.
CONDITIONS Low Impedance Source on VIN VIN = 2.5V, Not PGOOD VIN = 4.5V VIN = 18V ISW = 0A (Note 4) 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 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 l l l l l
MIN
TYP
MAX 18.0
UNITS V nA nA A A V V V V V V V V V mA mV nA V
450 950 1.7 150 3.77 3.77 4.73 4.73 2.66 2.66 3.42 3.75 19.0 25 350 400 4.04 4.04 5.05 5.05 2.87 2.87 3.67 4.02 20.0
700 1500 2.5 250 4.30 4.30 5.37 5.37 3.08 3.08 3.91 4.28 21.0 450 20
VUVLO
VSHUNT ISHUNT
VIN Shunt Regulator Voltage Maximum Protective Shunt Current Internal Bridge Rectifier Loss (|VPZ1 - VPZ2| - VIN) Internal Bridge Rectifier Reverse Leakage Current Internal Bridge Rectifier Reverse Breakdown Voltage
IVIN = 1mA 1ms Duration IBRIDGE = 10A VREVERSE = 18V IREVERSE = 1A 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 As a Percentage of the Selected VOUT VOUT = 3.6V
VSHUNT
30
VOUT
Regulated Output Voltage
l l l l l l l l
1.710 2.425 3.201 3.492 83 200 100
1.812 1.788 2.512 2.488 3.312 3.288 3.612 3.588 92 89 260 1.1 1.3
1.890 2.575 3.399 3.708
V V V V V V V V % nA mA mA % V
PGOOD Falling Threshold IVOUT IPEAK ILOAD RP RN VIH(D0, D1) VIL(D0, D1) IIH(D0, D1) IIL(D0, D1) Output Quiescent Current Buck Peak Switch Current Available Buck Output Current Buck PMOS Switch On-Resistance Buck NMOS Switch On-Resistance Max Buck Duty Cycle D0/D1 Input High Voltage D0/D1 Input Low Voltage D0/D1 Input High Current D0/D1 Input Low Current
150 350
l l l
100 1.2 0.4 10 10
V nA nA
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LTC3588-1 ELECTRICAL CHARACTERISTICS
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 0C to 85C. Specifications over the -40C to 85C operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. The LTC3588I-1 is guaranteed over the full -40C to 125C operating junction temperature range. 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 * JA). Note 4: Dynamic supply current is higher due to gate charge being
TYPICAL PERFORMANCE CHARACTERISTICS
IVIN in UVLO vs VIN
1000 900 800 700 IVIN (nA) 600 500 400 300 200 100 0 0 1 2 3 VIN (V) 4 5 6
35881 G01
IVIN in Sleep vs VIN
2400 85C 2200 2000 25C IVIN (nA) -40C 1800 1600 1400 1200 1000 800 600 400 2 4 6 8 10 12 VIN (V) 14 16 18 4.0 -40C 25C 85C UVLO RISING (V) 4.8 4.6 4.4 4.2 D1 = D0 = 0 5.2 5.0
UVLO Rising vs Temperature
D1 = D0 = 1
D1 = D0 = 1
D1 = D0 = 0
3.8 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G03
35881 G02
UVLO Falling vs Temperature
4.2 D1 = D0 = 1 4.0 UVLO FALLING (V) 3.8 3.6 3.4 3.2 3.0 2.8 -55 -35 -15 D1 = D0 = 0 5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G04
VSHUNT vs Temperature
21.0 20.8 20.6 VBRIDGE (mV) 1800 1600 1400 1200 1000 800 600 400 200 5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G05
Total Bridge Rectifier Drop vs Bridge Current
|VPZ1 - VPZ2| - VIN
D1 = 1, D0 = 0 VSHUNT (V)
20.4 20.2 20.0 19.8 19.6 19.4 19.2 19.0 -55 -35 -15 ISHUNT = 25mA ISHUNT = 1mA
-40C 85C 25C
0
1
10
100 1m BRIDGE CURRENT (A)
10m
35881 G06
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LTC3588-1 TYPICAL PERFORMANCE CHARACTERISTICS
Bridge Leakage vs Temperature
20 18 16 BRIDGE LEAKAGE (nA) 14 VIN (V) 12 10 8 6 4 2 0 -55 -10 35 80 125 TEMPERATURE (C) 170
35881 G07
Bridge Frequency Response
2.0 4VP-P APPLIED TO PZ1/PZ2 INPUT 1.8 MEASURED IN UVLO 1.6 1.4 VOUT (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 10 100 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M
35881 G08
1.8V Output vs Temperature
1.85 SLEEP THRESHOLD 1.80 WAKE-UP THRESHOLD 1.75
VIN = 18V, LEAKAGE AT PZ1 OR PZ2
1.70 PGOOD FALLING 1.65
1.60 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G09
2.5V Output vs Temperature
2.55 SLEEP THRESHOLD 2.50 WAKE-UP THRESHOLD 2.45 VOUT (V) VOUT (V) 3.30 3.35
3.3V Output vs Temperature
3.65 SLEEP THRESHOLD 3.60 WAKE-UP THRESHOLD 3.25 VOUT (V) 3.20 3.15 3.10
3.6V Output vs Temperature
SLEEP THRESHOLD WAKE-UP THRESHOLD 3.55 3.50 3.45 3.40 3.35
2.40 2.35 2.30 PGOOD FALLING
3.05
PGOOD FALLING
PGOOD FALLING 3.30 3.25 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G12
2.25 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G10
3.00 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G11
VOUT Load Regulation
2.56 2.54 2.52 VOUT (V) VOUT (V) 2.50 2.48 2.46 2.44 VIN = 5V, L = 10H, D1 = 0, D0 = 1 2.56 2.54 2.52
VOUT Line Regulation
L = 10H, ILOAD = 100mA, D1 = 0, D0 = 1 120 110 100 90 IVOUT (nA) 80 70 60 50 40 30
IVOUT vs Temperature
VOUT = 3.6V
VOUT = 3.3V
2.50 2.48 2.46 2.44
VOUT = 2.5V VOUT = 1.8V
1
10
100 1m 10m LOAD CURRENT (A)
100m
35881 G13
4
6
8
10 12 VIN (V)
14
16
18
20 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G15
35881 G14
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LTC3588-1 TYPICAL PERFORMANCE CHARACTERISTICS
IPEAK vs Temperature
300 290 280 270 IPEAK (mA) 260 250 240 230 220 210 200 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G16
RDS(ON) of PMOS/NMOS vs Temperature
2.0 1.8 NMOS 1.6 RDS(ON) () 1.4 PMOS 1.2 1.0 0.8 -55 -35 -15 0V INDUCTOR CURRENT 200mA/DIV 0mA 5 25 45 65 85 105 125 TEMPERATURE (C)
35881 G17
Operating Waveforms
OUTPUT VOLTAGE 50mV/DIV AC-COUPLED SWITCH VOLTAGE 2V/DIV
5s/DIV VIN = 5V, VOUT = 3.3V ILOAD = 1mA L = 10H, COUT = 47F
35881 G18
Efficiency vs ILOAD, L = 10H
100 90 80 EFFICIENCY (%) EFFICIENCY (%) 70 60 50 40 30 20 10 0 1 10 VOUT = 3.6V VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V 100 1m 10m LOAD CURRENT (A) 100m
35881 G19
Efficiency vs VIN for ILOAD = 100mA, L = 10H
100 90 EFFICIENCY (%) 80 70 60 50 40 VOUT = 3.6V VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V 2 4 6 8 10 12 VIN (V) 14 16 18 95 85 75 65 55 45 35
Efficiency vs VIN for VOUT = 3.3V, L = 10H
VIN = 5V
ILOAD = 100mA ILOAD = 1mA ILOAD = 100A ILOAD = 50A ILOAD = 10A 4 6 8 10 12 VIN (V) 14 16 18
35881 G20
35881 G21
Efficiency vs ILOAD, L = 100H
100 90 80 EFFICIENCY (%) EFFICIENCY (%) 70 60 50 40 30 20 10 0 1 10 VOUT = 3.6V VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V 100 1m 10m LOAD CURRENT (A) 100m
35881 G22
Efficiency vs VIN for ILOAD = 100mA, L = 100H
100 90 EFFICIENCY (%) 80 70 60 50 40 VOUT = 3.6V VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V 2 4 6 8 10 12 VIN (V) 14 16 18 95 85 75 65 55 45 35
Efficiency vs VIN for VOUT = 3.3V, L = 100H
VIN = 5V
ILOAD = 100mA ILOAD = 100A ILOAD = 50A ILOAD = 30A ILOAD = 10A 4 6 8 10 12 VIN (V) 14 16 18
35881 G23
35881 G24
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LTC3588-1 PIN FUNCTIONS
PZ1 (Pin 1): Input connection for piezoelectric element or other AC source (used in conjunction with PZ2). PZ2 (Pin 2): Input connection for piezoelectric element or other 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 1F capacitor should be connected 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 this pin serves as an energy reservoir and input supply for the buck regulator. The VIN voltage is internally clamped to a maximum of 20V (typical). SW (Pin 5): Switch Pin for the Buck Switching Regulator. A 10H 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 drive for buck NMOS switch. Also serves as a logic high rail for output voltage select bits D0 and D1. A 4.7F capacitor should be connected from VIN2 to GND. This pin is not intended for use as an external system rail. D1 (Pin 8): Output Voltage Select Bit. D1 should be tied high to VIN2 or low to GND to select desired VOUT (see Table 1). D0 (Pin 9): Output Voltage Select Bit. D0 should be tied high to VIN2 or low to GND to select desired VOUT (see Table 1). PGOOD (Pin 10): Power good output is logic high when VOUT is above 92% of the target value. The logic high is referenced to the VOUT rail. GND (Exposed Pad Pin 11): Ground. The Exposed Pad should be connected to a continuous ground plane on the second layer of the printed circuit board by several vias directly under the LTC3588-1.
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LTC3588-1 BLOCK DIAGRAM
VIN 4 20V INTERNAL RAIL GENERATION 3 PZ1 1 5 SW CAP
7 PZ2 2 UVLO BUCK CONTROL
VIN2
11 GND SLEEP BANDGAP REFERENCE 8, 9 D1, D0 2 PGOOD COMPARATOR 10 PGOOD 6 VOUT
35881 BD
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LTC3588-1 OPERATION
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 to interface directly to a piezoelectric or alternative A/C power source, 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. 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 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 low-loss bridge rectifier has a total drop of about 400mV with typical piezo generated currents (~10A). 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. Undervoltage Lockout (UVLO) 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 capacitor. A wide (~1V) UVLO hysteresis window is employed with a lower threshold approximately 300mV above the selected regulated output voltage to prevent short cycling during buck power-up. When the input capacitor voltage is depleted below the UVLO falling threshold the buck converter 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. 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 not intended 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) 12 10 8 6 4 2 0 0 5 VIN (V)
35881 F01
VIN
VIN2 CAP 10 15
Figure 1. Ideal VIN, VIN2 and CAP Relationship
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, VOUT, and the inductor value. If the input voltage falls below the
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LTC3588-1 OPERATION
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 a low quiescent current sleep state that monitors the output voltage with a sleep comparator. During this operating mode load current is provided by the buck output capacitor. When the output voltage falls below the regulation point the buck regulator 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. When the sleep comparator signals that the output has reached the sleep threshold the buck converter may be in the middle of a cycle with current still flowing through the 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 switching is much greater than the sleep quiescent current, it is still a 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 the converter needs to transfer energy to the output is much less than the time it takes to accumulate energy. Thus, the buck 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 0 0 1 1 D0 0 1 0 1 VOUT 1.8V 2.5V 3.3V 3.6V VOUT QUIESCENT CURRENT (IVOUT) 44nA 62nA 81nA 89nA
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 through servicing VOUT which is discharged by its own leakage current. VIN crosses UVLO falling but PGOOD remains high until VOUT decreases to 92% of the desired regulation point. The PGOOD pin is designed to drive a microprocessor or other chip I/O and is not intended to drive higher current loads such as an LED.
6 5 4 3 2 PGOOD 1 0 CVIN = CVOUT = 100F VIN VIN = UVLO FALLING VOUT
VOLTAGE (V)
0
100 TIME (s)
200
300
35881 F02
Figure 2. PGOOD Operation During Transition to UVLO
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LTC3588-1 OPERATION
The D0/D1 inputs can be switched while in regulation as shown in Figure 3. If VOUT is programmed to a voltage with a PGOOD falling threshold above the old VOUT, PGOOD will transition low until the new regulation point is reached. When VOUT is programmed to a lower voltage, PGOOD will remain high through the transition.
5
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. After the output voltage is brought into regulation any excess energy 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 the regulated 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 to support a larger current for some duration. For example, a current burst could begin when PGOOD goes high and would continuously deplete the output capacitor until PGOOD went low.
COUT = 100F ILOAD = 100mA , D1=D0=0 D1=D0=1 D1=D0=0
4 VOUT VOLTAGE (V)
3
2
VOUT
1
PGOOD = LOGIC1
0
0
2
4
6
8 10 12 14 16 18 20 TIME (ms)
35881 F03
Figure 3. PGOOD Operation During D0/D1 Transition
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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 structure of the ceramic is compressed and internal dipole movement produces a voltage. Polymer elements comprised of 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 and short-circuit currents. Typically the open-circuit voltage and short-circuit currents increase with available vibrational energy as shown in Figure 4. Piezoelectric elements can be placed in series or in parallel to achieve desired opencircuit voltages.
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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 efficient energy accumulation from piezoelectric elements which can have short-circuit currents on the order of tens of microamps. Piezoelectric elements can be obtained from manufacturers listed in Table 2.
Table 2. Piezoelectric Element Manufacturers
Advanced Cerametrics Piezo Systems Measurement Specialties PI (Physik Instrumente) MIDE Technology Corporation Morgan Technical Ceramics www.advancedcerametrics.com www.piezo.com www.meas-spec.com www.pi-usa.us www.mide.com www.morganelectroceramics.com
9 PIEZO VOLTAGE (V) INCREASING VIBRATION ENERGY 6
3
0
0
10 20 PIEZO CURRENT (A)
30
35881 F04
The LTC3588-1 will gather energy and convert it to a useable output voltage to power microprocessors, wireless sensors, and wireless transmission components. Such a wireless sensor application may require much more peak power than a piezoelectric element can produce. However, the LTC3588-1 accumulates energy over a long period of time 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 over an energy accumulation cycle. For piezoelectric inputs the time between cycles could be minutes, hours, or longer depending on the selected capacitor values and the nature of the vibration source.
Figure 4. Typical Piezoelectric Load Lines for Piezo Systems T220-A4-503X
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LTC3588-1 APPLICATIONS INFORMATION
PZ1 VIN 1F 6V 10F 25V 4.7F 6V PZ2 PGOOD 10H CAP LTC3588-1 VIN2 D1 D0 GND
35881 F05a
EN 3.3V CORE 47F 6V
TX
MICROPROCESSOR GND
OUTPUT VOLTAGE 20mV/DIV AC-COUPLED
SW VOUT
LOAD CURRENT 25mA/DIV 5mA
35881 F05b
250s/DIV VIN = 5V L = 10H, COUT = 47F 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 be somewhere between the UVLO thresholds at this time and 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 more energy 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 load when operating sensors, and then draw a large load to transmit data. Figure 5 shows the LTC3588-1 responding smoothly to such a load step. Input and Output Capacitor Selection The input and output capacitors should be selected based on 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 buck can 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 of time 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 not reach the UVLO falling threshold which would halt energy transfer to the output. In general: 1 PLOAD tLOAD = CIN VIN 2 - VUVLOFALLING 2 2 VUVLOFALLING VIN VSHUNT
(
)
The above equation can be used to size the input capacitor to meet the power requirements of the output for the desired duration. Here is the average efficiency of the buck 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 the lower 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 determined by the following equation: t SLEEP = COUT 24mV ILOAD
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13
LTC3588-1 APPLICATIONS INFORMATION
This is true for output capacitors on the order of 100F or larger, but as the output capacitor decreases towards 10F delays in the internal sleep comparator along with the 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 10F is not recommended as VOUT 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 VOUT: I -I COUT = ( VOUT+ - VOUT- ) LOAD BUCK tLOAD Here VOUT+ is the value of VOUT when PGOOD goes high and VOUT- is the desired lower limit of VOUT. IBUCK is the average 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 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 10H to 22H, although inductor values outside this range may yield benefits in some applications. For typical applications, a value of 10H 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 CDRH2D18/LDNP 107AS-100M EPL3015-103ML MLP3225s100L XLP2010-163ML SLF7045T L (H) 10 10 10 10 10 100 MAX IDC (mA) 430 650 350 1000 490 500 MAX DCR () 0.180 0.145 0.301 SIZE in mm (L x W x H) 3x3x2 2.8 x 3 x 1.8 2.8 x 3 x 1.5 MANUFACTURER Sumida Toko Coilcraft TDK Coilcraft TDK
0.130 3.2 x 2.5 x 1.0 0.611 2.0 x 1.9 x 1.0 0.250 7.0 x 7.0 x 4.5
VIN2 and CAP Capacitors A 1F capacitor should be connected between VIN and CAP and a 4.7F 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 source is 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 to clamp VIN 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 VIN2 and CAP saving components and allowing a lower voltage , rating for the single VIN capacitor.
PIEZO SYSTEMS T220-A4-503X
PZ1 VIN VIN2 5.6V (OPTIONAL) 10F 6V CAP D1 D0 GND
PZ2 PGOOD LTC3588-1 SW VOUT 10H PGOOD VOUT 1.8V 10F 6V
35881 F06
Figure 6. Smallest Solution Size 1.8V Low Voltage Input Piezoelectric Power Supply
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14
LTC3588-1 APPLICATIONS INFORMATION
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 the bridges of each LTC3588-1 provide isolation. Input piezo energy 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 a single piezo as long as the piezo can support the sum total of the quiescent currents from each LTC3588-1. A piezo powered LTC3588-1 can also be used in concert with a battery connected to VIN to supplement the system if 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.
PIEZO SYSTEMS T220-A4-503X
PZ1 PGOOD1 10H 3.6V 10F 6V GND SW VOUT PGOOD LTC3588-1
PZ2 VIN 1F 6V CAP VIN2 D1 D0 4.7F 6V 10F 25V 10F 25V 4.7F 6V 1F 6V
PZ1 VIN CAP VIN2 D1 D0 GND
PZ2 PGOOD LTC3588-1 SW VOUT 10F 6V PGOOD2 10H 1.8V
35881 F07
Figure 7. Dual Rail Power Supply with Single Piezo and Automatic Supply Sequencing
PIEZO SYSTEMS T220-A4-503X
IR05H40CSPTR 1F 6V 9V BATTERY 100F 16V 4.7F 6V
PZ1 VIN CAP VIN2 D1 D0 GND
PZ2 PGOOD LTC3588-1 SW VOUT PZ1 PZ2 PGOOD 10H VOUT 3.3V 47F 6V
35881 F08
Figure 8. Piezo Energy Harvester with Battery Backup
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LTC3588-1 APPLICATIONS INFORMATION
DANGER! HIGH VOLTAGE! DANGEROUS AND LETHAL POTENTIALS ARE PRESENT IN OFFLINE CIRCUITS! 150k 120VAC 60Hz 150k 150k BEFORE PROCEEDING ANY FURTHER, THE READER IS WARNED THAT CAUTION MUST BE USED IN THE CONSTRUCTION, TESTING AND USE OF 150k OFFLINE CIRCUITS. EXTREME CAUTION MUST BE USED IN WORKING WITH PZ1 VIN 1F 6V 10F 25V 4.7F 6V CAP VIN2 D1 D0 GND
35881 F09
PZ2 PGOOD LTC3588-1 SW VOUT PGOOD 10H VOUT 3.6V 100F 6V
AND MAKING CONNECTIONS TO THESE CIRCUITS. REPEAT: OFFLINE CIRCUITS CONTAIN DANGEROUS, AC LINE-CONNECTED HIGH VOLTAGE POTENTIALS. USE CAUTION. ALL TESTING PERFORMED ON AN OFFLINE CIRCUIT MUST BE DONE WITH AN ISOLATION TRANSFORMER CONNECTED BETWEEN THE OFFLINE CIRCUIT'S INPUT AND THE AC LINE. USERS AND CONSTRUCTORS OF OFFLINE CIRCUITS MUST OBSERVE THIS PRECAUTION WHEN CONNECTING TEST EQUIPMENT TO THE CIRCUIT TO AVOID ELECTRIC SHOCK. REPEAT: AN ISOLATION TRANSFORMER MUST BE CONNECTED BETWEEN THE CIRCUIT INPUT AND THE AC LINE IF ANY TEST EQUIPMENT IS TO BE CONNECTED.
Figure 9. AC Line Powered 3.6V Buck Regulator with Large Output Capacitor to Support Heavy Loads
COPPER PANEL (12" 24")
PANELS ARE PLACED 6" FROM 2' 4' FLUORESCENT LIGHT FIXTURES PZ1 VIN PZ2 PGOOD LTC3588-1 CAP VIN2 D1 D0 GND SW VOUT
COPPER PANEL (12" 24")
PGOOD 10H 3.3V 10F 6V
1F 6V 10F 25V 4.7F 6V
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 9 shows the LTC3588-1 internal bridge rectifier connected to 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 are placed 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 electronic ballast. 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 shown in 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 the PZ1 or PZ2 pins. This can be combined with a battery backup connected to VIN with a blocking diode.
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16
LTC3588-1 APPLICATIONS INFORMATION
300 PZ1 IR05H4OCSPTR VIN PGOOD LTC3588-1 CAP VIN2 4.7F 6V D0 D1 GND 10F 6V
35881 F11
PZ2 PGOOD 10H SW VOUT VOUT 2.5V
+ -
5V TO 16V SOLAR PANEL 9V BATTERY
1F 6V 100F 25V
+
3F 2.7V NESS SUPER CAPACITOR ESHSR-0003CO-002R7
Figure 11. 5V to 16V Solar-Powered 2.5V Supply with Supercapacitor for Increased Output Energy Storage and Battery Backup
RS, 5.2 PG-1 THERMAL GENERATOR P/N G1-1.0-127-1.27 (TELLUREX) 5.4V
100 PZ1 VIN 1F 6V 1F 16V 4.7F 6V CAP VIN2 D0 D1 GND
35881 F12
PZ2 PGOOD LTC3588-1 SW VOUT PGOOD 10H VOUT 2.5V 47F 6V
Figure 12. Thermoelectric Energy Harvester
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17
LTC3588-1 PACKAGE DESCRIPTION
DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.675 0.05
0.38 0.10 10
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) RECOMMENDED 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 PIN 1 TOP MARK (SEE NOTE 6)
3.00 0.10 (4 SIDES)
1.65 0.10 (2 SIDES)
(DD) DFN 1103
5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES)
1 0.25 0.05 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD
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18
LTC3588-1 PACKAGE DESCRIPTION
MS Package 10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661 Rev E)
BOTTOM VIEW OF EXPOSED PAD OPTION
2.794 (.110
0.102 .004)
0.889 (.035
0.127 .005)
1
2.06 0.102 (.081 .004) 1.83 0.102 (.072 .004)
5.23 (.206) MIN
2.083 (.082
0.102 3.20 - 3.45 .004) (.126 - .136)
10
0.50 0.305 0.038 (.0197) (.0120 .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT
3.00 0.102 (.118 .004) (NOTE 3)
10 9 8 7 6
0.497 0.076 (.0196 .003) REF
4.90 0.152 (.193 .006) 0.254 (.010) GAUGE PLANE 0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) SEATING PLANE 1.10 (.043) MAX DETAIL "A" 0 - 6 TYP 12345
3.00 0.102 (.118 .004) (NOTE 4)
0.86 (.034) REF
0.17 -0.27 (.007 - .011) TYP
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
0.50 (.0197) BSC
0.1016 (.004
0.0508 .002)
MSOP (MSE) 0307 REV B
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Information 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
Piezoelectric 3.3V Power Supply with LDO Post Regulator for Reduced Output Ripple
VOUT RIPPLE PEAK-TO-PEAK (mV)
Peak-to-Peak Output Ripple vs COUT1
120 100 80 60 40 20 0 VOUT2 (LT3009-3.3) VOUT1 (LTC3588-1) COUT2 = 1F
PZ1 VIN 1F 6V 47F 25V 4.7F 6V
PZ2 PGOOD 10H VOUT1 3.6V IN GND COUT1 10F 6V
35881 TA02a
SHDN LT3009-3.3 OUT VOUT2 3.3V 20mA COUT2 1F 6V
CAP LTC3588-1 VIN2 D1 D0 GND
SW VOUT
10 COUT1 (F)
100
35881 TA02b
RELATED PARTS
PART NUMBER LT1389 LTC1540 LT3009 LT3652 LT3970 LT3971 LT3991 LTC3631 LTC3642 DESCRIPTION Nanopower Precision Shunt Voltage Reference Nanopower Comparator with Reference 3A IQ, 20mA Low Dropout Linear Regulator Power Tracking 2A Battery Charger for Solar Power 40V, 350mA Step-Down Regulator with 2.5A IQ 38V, 1.2A, 2MHz Step-Down Regulator with 2.8A IQ 55V, 1.2A 2MHz Step-Down Regulator with 2.8A IQ 45V, 100mA, Synchronous Step-Down Regulator with 12A IQ 45V, 50mA, Synchronous Step-Down Regulator with 12A IQ COMMENTS 800nA Operating Current, 1.25V/2.5V/4.096V , 0.3A IQ, Drives 0.01F Adjustable Hysteresis, 2V to 11V Input Range Low 3A IQ, 1.6V to 20V Range, 20mA Output Current MPPT for Solar, 4.95V to 32V, Up to 2A Charge Current Integrated Boost and Catch Diodes, 4.2V to 40V Operating Range 4.3V to 38V Operating Range, Low Ripple Burst Mode(R) Operation 4.3V to 55V Operating Range, Low Ripple Burst Mode Operation 4.5V to 45V Operating Range, Overvoltage Lockout Up to 60V 4.5V to 45V Operating Range, Overvoltage Lockout Up to 60V
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20 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0110 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2010

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