EVALUATION KIT AVAILABLE
MAX17710
Energy-Harvesting Charger and Protector
General Description
Features
The MAX17710 is a complete system for charging and
protecting micropower-storage cells such as Infinite Power
Solutions’ THINERGY® microenergy cells (MECs). The IC
can manage poorly regulated sources such as energyharvesting devices with output levels ranging from 1FW to
100mW. The device also includes a boost regulator circuit
for charging the cell from a source as low as 0.75V (typ).
An internal regulator protects the cell from overcharging.
S Integrated Power-Management IC for Energy
Storage and Load Management
S Lithium Charger
S 1.8V, 2.3V, or 3.3V LDO (150nA IQBATT)
S Lithium Cell Output Buffering
S Ultra-Thin, 3mm x 3mm x 0.5mm UTDFN Package
Ordering Information appears at end of data sheet.
Applications
Remote Wireless
Sensors
High-Temperature
Applications
Memory and Real-Time
Clock Backup
Military/DoD and
Aerospace
Semiactive RFID Tags
Toys
1µW Boost Charging
S Charger Overvoltage Shunt Protection
The device is available in an ultra-thin, 3mm x 3mm x
0.5mm 12-pin UTDFN package.
Medical Devices
S Lithium Cell Undervoltage Protection
Output voltages supplied to the target applications are
regulated using a low-dropout (LDO) linear regulator with
selectable voltages of 3.3V, 2.3V, or 1.8V. The output regulator operates in a selectable low-power or ultra-low-power
mode to minimize drain of the cell. Internal voltage protection prevents the cell from overdischarging.
Powered/Smart Cards
1nA Standby IQBATT
625nA Linear Charging
For related parts and recommended products to use with this part,
refer to: www.maximintegrated.com/MAX17710.related.
Simplified Operating Circuit
THINERGY
MEC101
BATT
RF OR OTHER
HIGH-VOLTAGE
SOURCE
CHG
PCKP
UNREGULATED
OUTPUT
SEL2
REG
REGULATED
OUTPUT
MAX17710
TEG, SOLAR,
OR OTHER
LOW-VOLTAGE
SOURCE
LX
AE
FB
EP GND PGND
LCE
LDO
CONTROL
SIGNALS
SEL1
THINERGY is a registered trademark of Infinite Power Solutions, Inc.
For pricing, delivery, and ordering information, please contact Maxim Direct at
1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
19-5872; Rev 2; 12/12
MAX17710
Energy-Harvesting Charger and Protector
ABSOLUTE MAXIMUM RATINGS
BATT to GND............................................................-0.3V to +6V
CHG to GND............................................................-0.3V to +6V
LX to PGND..............................................................-0.3V to +6V
GND to PGND.......................................................-0.3V to +0.3V
FB, AE, LCE, SEL1, SEL2, REG,
PCKP to GND........................................-0.3V to VBATT + 0.3V
CHG Continuous Current
(limited by power dissipation of package)....................100mA
Continuous Power Dissipation (TA = +70NC)
UTDFN (derate 15mW/NC above +70NC)....................1200mW
Operating Temperature Range........................... -40NC to +85NC
Junction Temperature......................................................+150NC
Storage Temperature Range............................. -65NC to +150NC
Lead Temperature (soldering, 10s).................................+300NC
Soldering Temperature (reflow).......................................+260NC
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCHG = +4.3V, Figure 1, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1)
PARAMETER
SYMBOL
CHG Input Maximum Voltage
CONDITIONS
Limited by shunt regulator (Note 2)
CHG Enable Threshold
VCE
CHG Quiescent Current
IQCHG
MIN
TYP
MAX
4.875
5.3
5.7
V
4.07
4.15
4.21
V
625
1300
nA
VCHG = 4.0V rising, VBATT = 4.0V
CHG Shunt Delay
25
CHG Input Shunt Limit
(Note 2)
CHG Maximum Input Current
VCHG input current limited by Absolute
Maximum Ratings
CHG-to-BATT Dropout Voltage
Fs
50
50
100
VCHG = 4.0V, ICHG = 1FA
45
VCHG = 4.0V, IBATT = -6mA
55
VCHG = 4.0V, IBATT = -20mA
65
VCHG = 4.0V, IBATT = -40mA
100
UNITS
mA
mA
mV
BATT REG
BATT Regulator Voltage
4.065
BATT Regulation Delay
BATT Quiescent Current
Maxim Integrated
IQBATT
4.125
4.160
VCHG = 4.2V, starting at 4V
30
Regulator in dropout;
VCHG = 4.15V, VBATT = 4.12V
450
1030
1
165
AE regulator on, boost off;
VCHG = 0V, VBATT = 4.0V, AE high
725
1650
LCE regulator on, boost off;
VBATT = 4.0V, LCE mode (Note 3)
150
550
Harvest standby (AE pulse low)
VCHG = 0V, VBATT = 2.1V to 4.0V
V
Fs
nA
2
MAX17710
Energy-Harvesting Charger and Protector
ELECTRICAL CHARACTERISTICS (continued)
(VCHG = +4.3V, Figure 1, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
LINEAR LDO REGULATOR
REG Voltage
REG Voltage, LCE Mode
(Note 3)
VPCKP = 4.0V, IREG = 50FA, SEL1 = open
3.22
3.3
3.37
VPCKP = 4.0V, IREG = 50FA, SEL1 = GND
2.25
2.3
2.375
VPCKP = 4.0V, IREG = 50FA, SEL1 = BATT
1.75
1.8
1.9
VPCKP = 4.0V, IREG = 50FA, SEL1 = open
2.9
3.3
3.7
VPCKP = 4.0V, IREG = 50FA, SEL1 = GND
2.1
2.3
2.5
VPCKP = 4.0V, IREG = 50FA, SEL1 = BATT
1.6
1.8
2.05
V
V
VREG = 2.15V, VPCKP = 3.8V, AE high
75
mA
REG Current Limit
VREG = 2.15V, VPCKP = 3.8V, LCE mode
(Note 3)
50
FA
REG Startup Time
VPCKP = 4.0V, AE rising, CREG = 1FF
LCE Threshold High (Note 4)
LCE Threshold Low (Note 5)
VIH-LCE
VIL-LCE
5.3
SEL1 = open
2.175
SEL1 = GND
1.575
SEL1 = BATT
1.30
ms
V
SEL1 = open
0.9
SEL1 = GND
0.6
SEL1 = BATT
0.5
V
PCKP REGULATOR
AE Threshold High
VIH-AE
AE Threshold Low
VIL-AE
1.13
V
0.15
VAE = 0V, persists < 1Fs
-2
FA
VAE = 0V, persists > 1Fs
1
nA
AE High Input Current
VAE = 3.6V
1
nA
PCKP Enable Threshold
REG enabled
PCKP Charge Current
VPCKP = 0V, VBATT = 2.2V
PCKP Impedance Ramp Rate
AE Low Input Current
3.7
3.78
V
mA
VBATT = 4.0V, resistance between BATT
and PCKP from high impedance to 5I
5
ms
5
s
0.5
ms
tUVLO1
VBATT = 2.15V, AE high, first ramp of
PCKP
BATT UVLO Delay
tUVLO2
VBATT = 2.15V, AE high, not first PCKP
ramp
Maxim Integrated
3.62
100
BATT Undervoltage Lockout
(UVLO) Delay
BATT UVLO Threshold
-4
V
AE regulator active, LCE regulator inactive
LCE regulator active, AE regulator inactive
1.990
2.15
3
2.30
V
3
MAX17710
Energy-Harvesting Charger and Protector
ELECTRICAL CHARACTERISTICS (continued)
(VCHG = +4.3V, Figure 1, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
BOOST REGULATOR
CHG Regulation Voltage
VBATT = 4.125V
4.3
4.5
4.7
V
Frequency
VBATT = 3.9V, VCHG = 3.95V
0.73
1
1.27
MHz
Boost Turn-On Time
FB Threshold
tBOOST-ON Design guidance, typical only
ns
Rising (enable)
0.485
0.75
1.0
FBOFF
Falling (disable), VCHG = 3.8V
0.22
0.25
0.27
FB Input Current Low
LX nMOS On-Resistance
850
FBON
VFB = GND, momentary
RDS-ON
600
V
nA
ILX = 20mA, VBATT = 3.8V, SEL2 = GND
0.275
0.5
0.7
ILX = 10mA, VBATT = 3.8V, SEL2 = open
4
8
12
I
Note 1: Specifications are 100% production tested at TA = +25NC. Limits over the operating temperature range are guaranteed by
design and characterization.
Note 2: Since the CHG shunt regulator has a 25Fs delay, the user must limit the voltage to the Absolute Maximum Rating until the
internal CHG shunt provides the voltage limit at the pin in response to 50mA input. Larger currents must be shunted with
an external clamp to protect the CHG pin from damage.
Note 3: LCE mode is entered by pulsing AE high, then pulsing AE low.
Note 4: For logic-high, connect LCE to the REG output. Do not connect to the BATT or PCKP pins.
Note 5: Since LCE is compared to the REG pin voltage for operation, the low-power regulator cannot be switched off under conditions where the REG output is shorted to GND.
Maxim Integrated
4
MAX17710
Energy-Harvesting Charger and Protector
Table 1. Summary of Typical Quiescent Current vs. Operating Conditions
NAME
MODE
CONDITIONS
IQBATT
(nA)
IQCHG
(nA)
TOTAL QUIESCENT
CURRENT (nA)
Standby
Cell Connection:
Regulator outputs off,
no charger present
Cell connected to circuit
during assembly
1
—
1 (from cell)
Shutdown
UVLO or Shutdown:
Regulator outputs off,
no charger present
VBATT falls below 2.15V
or AE and LCE pulsed low
1
—
1 (from cell)
Full Charge
Charger Present:
Regulator outputs off,
cell charging
VCHG = 4V,
VCHG > VBATT,
AE pulsed low
1
625
Dropout
Charge
Charger in Dropout:
Regulator outputs off,
charger present, but
below regulation voltage
VCHG = 4.15V,
VBATT = 4.12V,
AE pulsed low
450
—
450 (from cell)
AE Active
AE Regulator On:
Boost off, no charge
source present
AE pulsed high
725
—
725 (from cell)
AE and LCE
Active
AE and LCE Regulators
On: Boost off, no charge
source present
LCE pulsed high after AE
pulsed high
875
—
875 (from cell)
LCE Active
LCE Regulator On:
Boost off, no charge
source present
AE pulsed high, then LCE
pulsed high, then AE pulsed
low
150
—
150 (from cell)
Maxim Integrated
626 (from energy-harvesting
cell); can harvest down to
1μW
5
MAX17710
Energy-Harvesting Charger and Protector
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
5
VOLTS (V)
AE
3
REG
9
8
7
4
4
CHG
SOLAR
3
PCKP
1
TA = +85°C
6
5
TA = +25°C
4
2
2
MAX17710 toc03
LX
IDD (nA)
5
10
MAX17710 toc02
6
MAX17710 toc01
6
VOLTS (V)
IDD vs. VBATT OVERTEMPERATURE
LCE AND AE AND SEL1 = GND
BOOST STARTUP
REGULATOR STARTUP
3
2
1
TA = -40°C
1
0
0
TIME (ms)
4
TIME (µs)
IDD vs. VBATT OVERTEMPERATURE
LCE = VREG, AE, AND SEL1 = GND
IDD vs. VBATT OVERTEMPERATURE
AE = BATT, LCE, AND SEL1 = GND
190
2
0
8
775
MEC101 CELL CHARGE PROFILE
2.5mW CHARGE SOURCE
575
90
525
3.5
4.0
0.30
3.95
0.25
3.90
3.0
3.5
0.4
0.3
MAX17710 toc08
3.1
2.9
2.7
2.5
2.3
2.1
3.1
2.5
2.3
2.1
1.7
0
1.5
Maxim Integrated
50
100
LOAD (mA)
250
2.7
1.9
0
200
2.9
1.7
4.1
150
3.3
0.1
4.0
100
LCE LOAD REGULATION
1.9
3.9
50
3.5
0.2
VBATT (V)
0
0
REGULATOR VOLTAGE (V)
0.5
3.8
0.05
TIME (Minutes)
3.3
REGULATOR VOLTAGE (V)
0.6
3.7
0.10
AE LOAD REGULATION
0.7
0.15
3.85
4.0
3.5
MAX17710 toc07
0.8
0.20
VBATT
VBATT (V)
0.9
3.6
0.35
4.00
3.75
BOOST CIRCUIT BREAK-EVEN
THRESHOLD vs. CELL VOLTAGE
(STANDARD APPLICATION CIRCUIT)
3.5
0.40
3.80
VBATT (V)
1.0
0.45
150
200
MAX17710 toc09
3.0
TA = +25°C
TA = -40°C
110
0.50
IBATT
4.10
CELL VOLTAGE (V)
IDD (nA)
TA = +25°C
TA = -40°C
675
625
MAX17710 toc06
4.15
4.05
725
150
4.0
1.5
0
50
100
LOAD (µA)
6
CHARGE CURRENT (mA)
TA = +85°C
3.5
3.0
VBATT (V)
825
130
HARVEST SOURCE POWER (µW)
6
TA = +85°C
170
IDD (nA)
0
10
MAX17710 toc05
5
MAX17710 toc04
0
MAX17710
Energy-Harvesting Charger and Protector
Pin Configuration
TOP VIEW
BATT
1
CHG
2
FB
3
GND
+
12
PCKP
11
LCE
10
REG
4
9
SEL1
LX
5
8
SEL2
PGND
6
7
AE
MAX17710
EP
UTDFN
Pin Description
PIN
NAME
1
BATT
Cell Input. Connect to the positive terminal of the cell without a bypass capacitor.
2
CHG
Charge Input. The IC charges the cell from the power source applied to this pin. Connect to the
output of the boost circuit or directly to a 4.21V or higher charge source.
3
FB
4
GND
5
LX
6
PGND
FUNCTION
Boost Enable. The boost circuit is enabled by driving this pin above the FBON threshold. Afterwards,
the boost circuit is disabled by driving this pin below FBOFF.
Device Ground. Connect to system ground.
Boost Input. Controls current drive through inductor of external boost circuit.
Power Ground. Connect to system ground.
Active Enable. Pulse high to enable high-power regulator output. Pulse low to disable regulator
output.
7
AE
8
SEL2
Boost RDS-ON Select. Connect to system ground to select a boost RDS-ON of 0.5I for typical
applications.
9
SEL1
Regulator Voltage Select. Ground this pin to select a regulator output voltage of 2.3V, leave
disconnected for a regulator output voltage of 3.3V, or connect to the BATT pin for a regulator
output voltage 1.8V.
10
REG
Regulator Output. Connect to load circuit. Bypass to system ground with a 1FF (typ) capacitor.
11
LCE
Low-Current Enable. Pulse high to enable the low-current regulator output after the high-current
regulator output is already active. Pulse low to disable.
12
PCKP
—
EP
Maxim Integrated
Protected Output of Pack. Connect an external capacitor to PCKP to support energy buffering to
the load, especially in low-temperature applications (see Table 4). PCKP is used for pulsed current
storage.
Exposed Pad. Connect to GND.
7
MAX17710
Energy-Harvesting Charger and Protector
Block Diagram
BATT
PCKP
10µF
LINEAR CHARGE
AND IDEAL
DIODE CONTROL
THINERGY
MEC101
OVERDISCHARGE
AND UNDERVOLTAGE
PROTECTION
UNREGULATED
OUTPUT
MAX17710
REF
CHG
0.1µF
RF, SOLAR,
OR OTHER
HIGH-VOLTAGE
SOURCE
LOAD VDD
OUTPUT
LINEAR REG
1.0µF
5.3V SHUNT
PROTECTION
TO REJECT
OVERCHARGE
ZLLS410TA
REG
3.3V/2.3V/1.8V
SELECT
SEL 1
BATT
1.5µH
LX
DISABLE
47µF
AE
PGND
300kI
TEG, SOLAR,
OR OTHER
LOW-VOLTAGE
SOURCE
FBON
THRESHOLD
BOOST REG
MECHANICAL, RF,
PIEZO, OR OTHER
STATE
MACHINE
SEL2
FB
EVENT
DETECTOR
LOAD VDD
LCE
MICROCONTROLLER
GND
Maxim Integrated
8
MAX17710
Energy-Harvesting Charger and Protector
Detailed Description
remains active after the removal of the charge voltage.
The state of this latch is off when initial power is applied
to the BATT pin.
Operation
While charging, the device consumes approximately
625nA from the CHG source until the voltage on CHG
exceeds 4.15V. Above 4.15V, the IC enters dropout and
BATT quiescent current increases from 1nA to 450nA.
The MAX17710 controls two main functions related to management of an energy-harvesting application: charging a
low-capacity cell with overcharge protection and an LDO
regulator output with overdischarge protection. With the
exception of protection features, charging and regulation
functions operate completely independently of one another.
CHG Shunt
Whenever a harvest source pulls the CHG pin above
5.3V, an internal shunt regulator enables a path to GND
to limit the voltage at the CHG pin. The internal shunt
path can sustain currents up to 50mA. If it is possible for
the harvest source to exceed this power limit, an external
protection circuit is required to prevent damage to the
device. Figure 1 shows the typical application charge circuit harvesting from high-voltage charge sources. Note
that a 0.22FF on CHG is recommended for shunt stability
when charging from high-voltage sources.
Initial power-up of the device occurs when a cell is connected to the BATT pin. In this state, the device pulls only
1nA (typ) from the cell and LDO functions are disabled. Only
after a charger has been applied and VCHG rises above
4.15V (VCE) does the device initialize to full operation and
allow discharging.
Charge-Regulator Operation
The device charges the cell from an external energy
source connected to the CHG pin. Whenever the voltage on CHG is greater than the voltage on BATT, the
energy-harvesting circuit directly passes current to the
cell without any interaction from the device. When CHG
rises above VCE, the input linear regulator turns on to limit
the charging voltage to 4.125V and protects the cell from
overcharge. Also at this time, any UVLO is reset, allowing the LDO to power the application load. This release
of the lockout is latched by CHG exceeding VCE and
In the application circuit example, the cell is charged by
several high-voltage harvest sources. Whenever either harvest source voltage is higher than the cell voltage, charge
is transferred directly. If either charge source exceeds
4.15V, the device begins to limit current flow to regulate the
cell’s voltage to 4.125V. If either charge source exceeds
5.3V, the internal CHG shunt discharges up to 50mA
through the device to GND to protect the CHG pin.
LOAD VDD
THINERGY
MEC101
REG
BATT
1µF
SEL2
EVENT
DETECTOR
SEL1
AE
CHG
0.22µF
MECHANICAL,
RF, PIEZO,
OR OTHER
MAX17710
LOAD VDD
HIGH-VOLTAGE AC
CHARGING SOURCE
(SOLAR, PIEZO)
HIGH-VOLTAGE DC
CHARGING SOURCE
(SOLAR, PIEZO)
LX
LCE
MICROCONTROLLER
FB
GND
EP
PGND
PCKP
10µF
Figure 1. Typical Application Charge Circuit Harvesting from High-Voltage Charge Sources
Maxim Integrated
9
MAX17710
Energy-Harvesting Charger and Protector
Boost Regulator Operation
driving FB below the FBOFF threshold, which disables
the boost circuit. The process repeats after the harvest
source capacitor is recharged.
The device includes a simple boost regulator controller to
support energy harvesting from low-voltage solar or thermoelectric generator (TEG) devices. The boost converter
can harvest energy down to approximately 1FW when
operated in pulsed harvest mode and as high as 100mW
in continuous conversion. For a 0.8V harvest source and
a 4.1V cell, the device can deliver over 20mA (80mW), as
long as the harvest source can support it. Figure 2 shows
the typical application boost circuit boost harvesting
from a low-voltage solar-cell array.
Because the boost converter draws its quiescent current
directly from the cell (for startup reasons), it is important
to only enable the boost converter when it can provide
more power than the boost converter consumes from the
cell. This can be guaranteed as long as the capacitor
across the TEG is large enough to boost CHG above the
BATT pin. Note that it is important to use a high-speed
Schottky diode between LX and CHG to guarantee LX
does not exceed its absolute maximum voltage rating
during boost operation.
In the application circuit example, the solar cell array
charges the 47FF harvest-source capacitor until the voltage on FB exceeds the FBON threshold. At this time, the
LX pin is pulled low to force current through the external
inductor. LX begins to oscillate at a fixed 1.0MHz with
90% duty cycle. Each time LX is released by the device,
the external inductor forces the voltage of LX above CHG
and charges the 0.1FF CHG pin capacitor. When CHG
rises above the voltage of VBATT, charge is delivered to
the cell. If the CHG pin exceeds 4.5V during this time,
the boost converter enters a skip-mode operation to
limit voltage on CHG to 4.5V. Operation continues until
the voltage of the harvest-source capacitor collapses,
Charge Regulator Component Selection
External component selection depends on the charge
sources available to the device. Proper component
selection provides the highest efficiency operation of the
IC during energy harvesting. See Figure 2 as a reference.
This section describes component selection for boost
sources with operational voltages of 1.0V or high-voltage
sources. For boost charge sources with operational voltages between 1.0V and 2.0V, additional components
are required. See the FB Divider section for a detailed
description.
LOAD VDD
THINERGY
MEC101
REG
BATT
1µF
SEL2
SEL1
EVENT
DETECTOR
CHG
0.1µF
AE
ZLLS410TA
HIGH-SPEED
SCHOTTKY
MAX17710
MECHANICAL,
RF, PIEZO,
OR OTHER
LOAD VDD
1.5µH
LX
SOLAR CELL 2
SOLAR CELL 1
47µF
300kI
LCE
FB
GND
EP
PGND
MICROCONTROLLER
PCKP
10µF
Figure 2. Typical Application Boost Circuit Boost Harvesting from a Low-Voltage Solar-Cell Array
Maxim Integrated
10
MAX17710
Energy-Harvesting Charger and Protector
CHG Capacitor
The CHG pin capacitor should be minimized to 0.1FF
for highest charge efficiency. However, when charging
from a high-voltage source, at least 0.22FF is required
for shunt stability.
LX Inductor
The LX pin inductor is not required for high-voltage
charge sources. For low-voltage sources, a minimum
inductor value of 0.68FH is required to prevent the maximum current rating of the LX pin from being exceeded.
Minimum inductor value is calculated as follows:
LX inductor = VFB-ON x tBOOST-ON/LXIMAX = 1.0V x
850ns/1A = 0.85FH
Boost Diode
The boost circuit diode must be a high-speed Schottky,
such as the ZLLS410TA from Diodes Incorporated. The
diode must turn on quickly to clamp the LX pin voltage rise at 6.0V or lower when the LX driver turns off.
The LX pin can be damaged if the maximum voltage is
exceeded.
Harvest Source Capacitor
The harvest source capacitor must be a minimum of 70
times larger than the CHG pin capacitor to boost the
charge pin to the maximum charge voltage under worstcase conditions:
Source capacitor = (4.125V)2/(0.485V)2 x
CHG capacitor
This is the minimum size required for operation. Increasing
the size of the harvest source capacitor beyond this
level improves charge circuit efficiency at extremely low
input power (< 10FW), but care should be taken not to
increase the capacitor so large that the harvest source
cannot overcome the capacitor’s leakage. A maximum
value of 47FF is recommended.
Table 2 lists boost converter external component values.
Minimum capacitor and inductor values are required for
proper operation of the charge circuit. Recommended
capacitor and inductor values provide optimum charge
efficiency. Components should be sized as close to
the recommended values that the application allows.
Component values below the minimum values, or above
the optimum values, are not recommended.
FB Divider
Charge sources with operational voltages between 1.0V
and 2.0V require boosting, but are too high a voltage to
control the boost circuit efficiently. Under these conditions, a voltage-divider is required to lower the voltage
seen by the FB pin (see Figure 3). The divider formed by
R1 and R2 allows the voltage on the FB pin to transition
properly between the FBON and FBOFF thresholds during
boosting. The value for R2 is calculated as follows:
VHARVEST-ON = FBON x (R1 + R2)/R1
R2 = (VHARVEST-ON - 1.0V) x 500kI
where VHARVEST-ON is the operational voltage of the
harvest source.
Table 2. Boost Converter External Component Values
APPLICATION
CHARGE SOURCE
CHG
CAPACITOR
(µF)
MINIMUM LX
INDUCTOR
(µH)
RECOMMENDED
LX INDUCTOR
(µH)
MINIMUM
HARVEST SOURCE
CAPACITOR (µF)
RECOMMENDED
HARVEST SOURCE
CAPACITOR (µF)
N/A
High voltage
0.22
N/A
N/A
N/A
Low voltage < 10FW
0.1
0.85
1.5
7.0
47
Low voltage > 10FW
0.1
0.85
1.5
7.0
7.0
High voltage and low
voltage < 10FW
0.22
0.85
1.5
15.4
47
High voltage and low
voltage > 10FW
0.22
0.85
1.5
15.4
15.4
Maxim Integrated
11
MAX17710
Energy-Harvesting Charger and Protector
The C1 1nF capacitor acts as a voltage-level feed forward to increase the responsiveness of the divider circuit
as the harvest source capacitor is discharged. The minimum voltage is defined as:
CHG
0.1µF
VHARVEST-OFF ~= VHARVEST-ON - (FBON - FBOFF)
ZLLS410TA
VHARVEST-OFF ~= VHARVEST-ON - 0.5V (typ)
where VHARVEST-OFF is the lowest voltage of the harvest
source capacitor during boost.
Because of the divider on the FB pin, the voltage seen by
the LX pin inductor is higher than the typical circuit. The
inductor must be resized so that the LX pin current limits
are not exceeded:
MAX17710
L1
1.0V TO 2.0V
CHARGE
SOURCE
LX
47µF
C1
1nF
R2
FB
LX Inductor = VHARVEST-ON x tBOOST-ON/LXIMAX =
VHARVEST-ON x (8.5 x 10-7)
R1
500kI
All other components are selected as normal.
Energy-Harvesting Design Approaches
Figure 3. FB Divider Circuit to Improve Boost Efficiency for
Charge Sources Between 1.0V and 2.0V
MPPT
(MAX POWER
TRACKING)
BOOST HARVEST
CHARGE EFFICIENCY
When designing an optimal energy harvest system,
there are three types of design approaches: linear harvest, boost harvest, and maximum-power-point tracking
(MPPT). In harvesting applications, it is very critical to
not discharge the cell when charging is failing. When
the harvesting power is low enough, eventually the system discharges the cell rather than charges. This is the
break-even point of the harvester. For linear harvesting,
this break-even point is lower because the required
quiescent current is less. However, for boost harvesting,
the breakeven threshold is 1FA. While an MPPT system
can utilize the harvesting source more intelligently in
high-power situations, it inevitably results in higher quiescent current and a poorer break-even threshold. MPPT
systems must measure the current and voltage, multiply
to determine power, and make decisions to improve the
power. These required measurements automatically
significantly increase the quiescent current budget
by tens of µA. Figure 4 shows energy-harvesting modes
of operation vs. charge efficiency.
LINEAR
HARVEST
BREAK-EVEN
THRESHOLDS
LDO Output Operation
The device regulates voltage from the cell to a load
circuit on the REG pin through an LDO regulator. The
regulator can be configured for 3.3V, 2.3V, or 1.8V operation. The LDO supports loads up to 75mA (high-current
mode). For lighter load applications, a low-power mode
of operation reduces the quiescent current drain on the
cell. A UVLO circuit prevents the regulator from starting up or disabling the regulator when active if the cell
becomes overdischarged.
Maxim Integrated
POWER FROM HARVEST SOURCE
Figure 4. Energy-Harvesting Modes of Operation vs. Charge
Efficiency
12
MAX17710
Energy-Harvesting Charger and Protector
The LDO becomes active when the AE pin is pulsed
above or held above its logic-high threshold, but the
regulator output is not immediately enabled. The device
first charges the external capacitor on PCKP. When the
voltage level on PCKP reaches 3.7V, the regulator output
is enabled in high-current mode. Powering the LDO from
PCKP instead of directly from the cell allows the device
to support large surge or startup inrush currents from the
load that the cell would be unable to handle directly.
Once in high-current mode, the AE pin can remain logichigh or transition to an open state, and the ouput remains
active. The LDO returns to shutdown only when the AE
pin is driven below its logic-low threshold. Alternatively,
the LDO is transitioned to low-current mode by pulsing
or holding the LCE to the REG pin voltage, followed by
pulsing or holding the AE pin logic-low. Note that the
regulator transitions through a state where both highcurrent and low-current modes are active at the same
time. While in low-current mode, the quiescent current
drain of the cell is reduced to 150nA, while the maximum
load current able to be supplied becomes 50FA. Similar
to the AE pin operation, the regulator remains active if the
LCE pin is open or pulled to REG, and returns to shutdown
mode when LCE is driven below its logic-low threshold.
Figure 5 is the regulator output state diagram.
Cell Undervoltage Lockout (UVLO)
If the cell and PCKP capacitance cannot provide sustained support for the load, then the voltage at PCKP collapses. When PCKP collapses, the system load typically
stops and allows the PCKP voltage to recover, resulting
in a perpetual retry in a futile attempt to support a load
that cannot be supported. When PCKP fails in this way,
the device shuts off the REG output to prevent futile load
retries and protect the cell from overdischarge. When the
REG output is latched off, the BATT quiescent current
reduces to 1nA (typ). Once UVLO occurs, the regulator
output remains disabled until the device detects that a
charge source has been connected to the system (VCHG
> 4.15V). Figure 6 shows the UVLO protection modes.
Connecting any load to REG or PCKP instead of connecting directly to the cell is highly recommended. This controls the quiescent current during shutdown, enables the
device to support startup during cold, and also protects
the cell from overdischarge.
LCE PULSED LOW
SHUTDOWN
PCKP OFF
REG OFF
IQBATT = 1nA (typ)
AE PULSED LOW
AE PULSED HIGH
STARTUP
CHARGE
DETECTED
VCHG > VCE
PCKP ON
REG OFF
IQBATT = PCKP CAPACITOR
CHARGE CURRENT
+ 725nA (typ)
STARTUP
SUCCESS
VPCKP > 3.7V
STARTUP FAIL
VPCKP < 2.15V
AFTER 5s
AE REGULATOR
ACTIVE
PCKP ON
REG ON
IQBATT = 725nA (typ)
LCE PULSED
HIGH
LCE PULSED
LOW
AE AND LCE
REGULATORS ACTIVE
PCKP ON
REG ON
IQBATT = 875nA (typ)
AE PULSED
LOW
AE PULSED
HIGH
LCE REGULATOR
ACTIVE
PCKP ON
REG ON
IQBATT = 150nA (typ)
CELL UNDERVOLTAGE
VPCKP < 2.15V (HIGH-CURRENT MODE)
VPCKP < 3.0V (LOW-CURRENT MODE)
AFTER 500µs
UNDERVOLTAGE
LOCKOUT
PCKP OFF
REG OFF
IQBATT = 1nA (typ)
POWER-ON RESET (POR)
Figure 5. Regulator Output State Diagram
Maxim Integrated
13
MAX17710
Energy-Harvesting Charger and Protector
4.1V
BATT
4.1V
BATT
2.15V
0V
2.15V
0V
4.1V
PCKP
4.1V
3.7V
PCKP
0V
0V
AE
VOH-AE
VOH-AE
AE
VOL-AE
VOL-AE
3.3V
REG
UVLO
0V
0V
a. NORMAL REGULATOR OUTPUT ENABLE SEQUENCE
> tUVLO1
(5s typ)
b. REGULATOR OUTPUT ENABLE FAIL DUE TO UVLO TIMEOUT
4.1V
BATT
2.15V
0V
4.1V
PCKP
2.15V
BATT
4.1V
3.0V
PCKP
0V
0V
3.3V
REG
3.3V
0V
4.1V
REG
0V
> tUVLO2
(500µs typ)
UVLO
UVLO
0V
0V
c. HIGH-CURRENT MODE REGULATOR OUTPUT DISABLED DUE TO UVLO TIMEOUT
d. LOW-CURRENT MODE REGULATOR OUTPUT DISABLED DUE TO UVLO DETECTION
Figure 6. ULVO Protection Modes
Maxim Integrated
14
MAX17710
Energy-Harvesting Charger and Protector
Regulator Voltage Selection
The SEL1 pin selects at which voltage REG operates.
Connect SEL1 to BATT for 1.8V operation, three-state for
3.3V operation, or connect to GND for 2.3V operation.
Note that the voltage regulation value is latched when
enabled. To change the regulation voltage point, the regulator must be disabled and then reenabled. See Table 3.
PCKP Pin Capacitor Selection
There are several cases when the system might overload
the cell, potentially causing damage. They are prevented
with the PCKP load switch block and external capacitor:
U During startup, when there is an inrush current due to
the application’s load and capacitance.
U When the cell is cold (such as -40NC), and due to
increased cell resistance, it is unable to support highload currents.
U If the system requires a load current higher than can be
supported by the cell alone.
The device provides cell undervoltage protection by
limiting the current from BATT to PCKP and guaranteeing that the cell voltage does not fall below 2.15V. In
addition to voltage protection, the ramp of the PCKP
switch impedance is changed slowly (5ms to full on) to
gradually load the cell and not collapse the voltage on a
room-temperature cell. Because of these protection features, an application can now support brief high-current
pulses by including a large capacitance at PCKP. This
allows support for pulse loads many times higher than
that naturally supported by the cell alone.
A large PCKP capacitance can be selected to support
a pulse load even while the cell is very cold, and would
normally be incapable of supporting a significant load.
Choose this capacitor according to Table 4 or the following equation:
CPCKP = ITASK x tTASK/(3.7 - VMIN)
where:
ITASK is the current required to sustain a required task,
tTASK is the time duration of the task, and VMIN is the
minimum voltage of the load doing the task.
This equation assumes that the BATT impedance is high
and cannot support the load.
Table 3. Regulator Output Voltage Selection
SEL1 PIN CONNECTION
REG PIN OUTPUT VOLTAGE (V)
Connect to BATT
1.8
Open circuit
3.3
Connect to GND
2.3
Table 4. PCKP Pin Capacitor Values by Application
VMIN
tTASK (ms)
ITASK (mA)
CPCKP (µF)*
3.0
5
8
100
3.0
5
4
50
2.8
5
5
28
2.8
5
2.5
14
2.3
5
5
18
10
36
2.3
5
*Capacitance value tolerances need to be considered.
Maxim Integrated
15
MAX17710
Energy-Harvesting Charger and Protector
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but the
drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
12 UTDFN-EP
V1233N+1
21-0451
90-0339
Maxim Integrated
Ordering Information
PART
MAX17710G+T*
TEMP RANGE
PIN-PACKAGE
-40NC to +85NC
12 UTDFN-EP**
MAX17710G+U*
-40NC to +85NC
12 UTDFN-EP**
MAX17710GB+
-40NC to +85NC
12 UTDFN-EP**
MAX17710GB+T
-40NC to +85NC
12 UTDFN-EP**
+Denotes a lead(Pb)-free/RoHS-compliant package.
U = Signifies tape cut.
T = Tape and reel.
*Not recommended for new designs.
**EP = Exposed pad.
16
MAX17710
Energy-Harvesting Charger and Protector
Revision History
REVISION
NUMBER
REVISION
DATE
0
12/12
DESCRIPTION
Initial release
PAGES
CHANGED
—
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
© 2012 Maxim Integrated Products, Inc.
17
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
MAX17710
Energy-Harvesting Charger and Protector
Maxim Integrated
18
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