MAX17710_13 [MAXIM]
Energy-Harvesting Charger and Protector; 能量收集充电器和保护型号: | MAX17710_13 |
厂家: | MAXIM INTEGRATED PRODUCTS |
描述: | Energy-Harvesting Charger and Protector |
文件: | 总18页 (文件大小:1547K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
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 energy-
harvesting 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
1nA Standby I
QBATT
625nA Linear Charging
1µW Boost Charging
S Lithium Cell Undervoltage Protection
S Charger Overvoltage Shunt 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 regu-
lator operates in a selectable low-power or ultra-low-power
mode to minimize drain of the cell. Internal voltage protec-
tion prevents the cell from overdischarging.
S 1.8V, 2.3V, or 3.3V LDO (150nA I
S Lithium Cell Output Buffering
)
QBATT
S Ultra-Thin, 3mm x 3mm x 0.5mm UTDFN Package
The device is available in an ultra-thin, 3mm x 3mm x
0.5mm 12-pin UTDFN package.
Ordering Information appears at end of data sheet.
Applications
For related parts and recommended products to use with this part,
refer to: www.maximintegrated.com/MAX17710.related.
Powered/Smart Cards
Medical Devices
Remote Wireless
Sensors
High-Temperature
Applications
Memory and Real-Time
Clock Backup
Military/DoD and
Aerospace
Semiactive RFID Tags
Toys
Simplified Operating Circuit
UNREGULATED
OUTPUT
THINERGY
MEC101
PCKP
BATT
SEL2
CHG
RF OR OTHER
HIGH-VOLTAGE
SOURCE
REGULATED
OUTPUT
REG
MAX17710
TEG, SOLAR,
OR OTHER
LX
LOW-VOLTAGE
SOURCE
LDO
AE
CONTROL
SIGNALS
FB
EP
LCE
GND
PGND 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,
Continuous Power Dissipation (T = +70NC)
A
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
PCKP to GND.......................................-0.3V to V
CHG Continuous Current
+ 0.3V
BATT
(limited by power dissipation of package) ...................100mA
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional opera-
tion 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
(V
= +4.3V, Figure 1, T = -40NC to +85NC, unless otherwise noted. Typical values are at T = +25NC.) (Note 1)
A A
CHG
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
5.3
MAX
5.7
UNITS
CHG Input Maximum Voltage
CHG Enable Threshold
Limited by shunt regulator (Note 2)
4.875
4.07
V
V
V
4.15
4.21
CE
CHG Quiescent Current
CHG Shunt Delay
I
V
= 4.0V rising, V = 4.0V
BATT
625
25
1300
nA
Fs
QCHG
CHG
CHG Input Shunt Limit
(Note 2)
input current limited by Absolute
Maximum Ratings
50
mA
V
CHG
CHG Maximum Input Current
50
100
mA
V
V
V
V
= 4.0V, I
= 4.0V, I
= 4.0V, I
= 4.0V, I
= 1FA
45
55
CHG
CHG
CHG
CHG
CHG
BATT
BATT
BATT
= -6mA
= -20mA
= -40mA
CHG-to-BATT Dropout Voltage
mV
65
100
BATT REG
BATT Regulator Voltage
BATT Regulation Delay
4.065
4.125
30
4.160
V
V
= 4.2V, starting at 4V
Fs
CHG
Regulator in dropout;
= 4.15V, V
450
1
1030
165
V
= 4.12V
BATT
CHG
Harvest standby (AE pulse low)
= 0V, V = 2.1V to 4.0V
V
CHG
BATT
BATT Quiescent Current
I
QBATT
nA
AE regulator on, boost off;
= 0V, V = 4.0V, AE high
725
150
1650
550
V
CHG
BATT
LCE regulator on, boost off;
= 4.0V, LCE mode (Note 3)
V
BATT
Maxim Integrated
2
MAX17710
Energy-Harvesting Charger and Protector
ELECTRICAL CHARACTERISTICS (continued)
(V
= +4.3V, Figure 1, T = -40NC to +85NC, unless otherwise noted. Typical values are at T = +25NC.) (Note 1)
A A
CHG
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
LINEAR LDO REGULATOR
V
V
V
V
V
V
V
V
= 4.0V, I
= 50FA, SEL1 = open
3.22
2.25
1.75
2.9
3.3
2.3
1.8
3.3
2.3
1.8
3.37
2.375
1.9
PCKP
PCKP
PCKP
PCKP
PCKP
PCKP
REG
REG
REG
REG
REG
REG
REG Voltage
= 4.0V, I
= 4.0V, I
= 4.0V, I
= 4.0V, I
= 4.0V, I
= 50FA, SEL1 = GND
= 50FA, SEL1 = BATT
= 50FA, SEL1 = open
= 50FA, SEL1 = GND
= 50FA, SEL1 = BATT
V
3.7
REG Voltage, LCE Mode
(Note 3)
2.1
2.5
V
1.6
2.05
= 2.15V, V
= 3.8V, AE high
75
mA
FA
REG
PCKP
REG Current Limit
= 2.15V, V
= 3.8V, LCE mode
REG
PCKP
50
(Note 3)
REG Startup Time
V
= 4.0V, AE rising, C = 1FF
REG
5.3
ms
PCKP
SEL1 = open
SEL1 = GND
SEL1 = BATT
SEL1 = open
SEL1 = GND
SEL1 = BATT
2.175
1.575
1.30
LCE Threshold High (Note 4)
V
V
V
IH-LCE
0.9
0.6
0.5
LCE Threshold Low (Note 5)
V
IL-LCE
PCKP REGULATOR
AE Threshold High
AE Threshold Low
V
1.13
-4
V
V
IH-AE
V
0.15
3.78
IL-AE
V
V
V
= 0V, persists < 1Fs
= 0V, persists > 1Fs
= 3.6V
-2
1
FA
nA
nA
V
AE
AE
AE
AE Low Input Current
AE High Input Current
PCKP Enable Threshold
PCKP Charge Current
1
REG enabled
3.62
3.7
100
V
= 0V, V
= 2.2V
mA
PCKP
BATT
BATT
V
= 4.0V, resistance between BATT
PCKP Impedance Ramp Rate
5
5
ms
s
and PCKP from high impedance to 5I
BATT Undervoltage Lockout
(UVLO) Delay
V
= 2.15V, AE high, first ramp of
BATT
t
t
UVLO1
PCKP
V
ramp
= 2.15V, AE high, not first PCKP
BATT
BATT UVLO Delay
0.5
ms
V
UVLO2
AE regulator active, LCE regulator inactive
LCE regulator active, AE regulator inactive
1.990
2.15
3
2.30
BATT UVLO Threshold
Maxim Integrated
3
MAX17710
Energy-Harvesting Charger and Protector
ELECTRICAL CHARACTERISTICS (continued)
(V
= +4.3V, Figure 1, T = -40NC to +85NC, unless otherwise noted. Typical values are at T = +25NC.) (Note 1)
A A
CHG
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
BOOST REGULATOR
CHG Regulation Voltage
Frequency
V
V
= 4.125V
4.3
4.5
1
4.7
V
BATT
BATT
= 3.9V, V
= 3.95V
0.73
1.27
MHz
ns
CHG
Boost Turn-On Time
t
Design guidance, typical only
Rising (enable)
850
0.75
0.25
600
0.5
8
BOOST-ON
FB
0.485
0.22
1.0
ON
FB Threshold
V
nA
I
FB
Falling (disable), V
= 3.8V
0.27
OFF
CHG
FB Input Current Low
LX nMOS On-Resistance
V
= GND, momentary
FB
I
I
= 20mA, V
= 3.8V, SEL2 = GND
= 3.8V, SEL2 = open
0.275
4
0.7
12
LX
BATT
R
DS-ON
= 10mA, V
LX
BATT
Note 1: Specifications are 100% production tested at T = +25NC. Limits over the operating temperature range are guaranteed by
A
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 condi-
tions 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
I
I
TOTAL QUIESCENT
CURRENT (nA)
QBATT
(nA)
QCHG
(nA)
NAME
MODE
CONDITIONS
Cell Connection:
Regulator outputs off,
no charger present
Cell connected to circuit
during assembly
Standby
1
1
1
—
—
1 (from cell)
UVLO or Shutdown:
Regulator outputs off,
no charger present
V
falls below 2.15V
BATT
Shutdown
1 (from cell)
or AE and LCE pulsed low
Charger Present:
Regulator outputs off,
cell charging
V
V
= 4V,
626 (from energy-harvesting
cell); can harvest down to
1µW
CHG
Full Charge
> V
625
CHG
BATT,
AE pulsed low
Charger in Dropout:
V
V
= 4.15V,
= 4.12V,
CHG
Dropout
Charge
Regulator outputs off,
charger present, but
below regulation voltage
450
—
450 (from cell)
BATT
AE pulsed low
AE Regulator On:
Boost off, no charge
source present
AE Active
AE pulsed high
725
875
150
—
—
—
725 (from cell)
875 (from cell)
150 (from cell)
AE and LCE Regulators
On: Boost off, no charge
source present
AE and LCE
Active
LCE pulsed high after AE
pulsed high
LCE Regulator On:
Boost off, no charge
source present
AE pulsed high, then LCE
pulsed high, then AE pulsed
low
LCE Active
Maxim Integrated
5
MAX17710
Energy-Harvesting Charger and Protector
Typical Operating Characteristics
(T = +25°C, unless otherwise noted.)
A
I
DD
vs. V
OVERTEMPERATURE
BATT
BOOST STARTUP
REGULATOR STARTUP
LCE AND AE AND SEL1 = GND
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
6
5
4
3
2
1
0
LX
T
A
= +85°C
CHG
SOLAR
AE
T
A
= +25°C
REG
PCKP
T
= -40°C
(V)
A
2
4
6
8
0
3.0
3.5
V
4.0
0
5
10
TIME (µs)
TIME (ms)
BATT
MEC101 CELL CHARGE PROFILE
2.5mW CHARGE SOURCE
I
vs. V
OVERTEMPERATURE
I
vs. V
OVERTEMPERATURE
DD
BATT
DD
BATT
LCE = VREG, AE, AND SEL1 = GND
AE = BATT, LCE, AND SEL1 = GND
MAX17710 toc06
825
775
725
675
625
575
525
4.15
4.10
4.05
4.00
3.95
3.90
3.85
3.80
3.75
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
190
170
150
130
110
90
I
BATT
T
= +85°C
= +25°C
A
A
T
= +85°C
= +25°C
A
A
V
BATT
T
T
T
= -40°C
A
T
= -40°C
A
3.0
3.5
V
4.0
0
50
100
150
200
250
3.0
3.5
V
4.0
(V)
TIME (Minutes)
(V)
BATT
BATT
BOOST CIRCUIT BREAK-EVEN
THRESHOLD vs. CELL VOLTAGE
(STANDARD APPLICATION CIRCUIT)
AE LOAD REGULATION
LCE LOAD REGULATION
3.5
3.3
3.1
2.9
2.7
2.5
2.3
2.1
1.9
1.7
1.5
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
3.5
3.3
3.1
2.9
2.7
2.5
2.3
2.1
1.9
1.7
1.5
0
50
100
150
200
3.5
3.6
3.7
3.8
3.9
4.0
4.1
0
50
100
LOAD (mA)
V
(V)
LOAD (µA)
BATT
Maxim Integrated
6
MAX17710
Energy-Harvesting Charger and Protector
Pin Configuration
TOP VIEW
+
1
2
3
4
5
6
BATT
CHG
FB
PCKP
LCE
12
11
10
9
REG
SEL1
SEL2
AE
MAX17710
GND
LX
8
EP
PGND
7
UTDFN
Pin Description
PIN
NAME
FUNCTION
1
BATT
Cell Input. Connect to the positive terminal of the cell without a bypass capacitor.
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.
2
3
CHG
FB
Boost Enable. The boost circuit is enabled by driving this pin above the FB
threshold. Afterwards,
ON
the boost circuit is disabled by driving this pin below FB
.
OFF
4
5
6
GND
LX
Device Ground. Connect to system ground.
Boost Input. Controls current drive through inductor of external boost circuit.
Power Ground. Connect to system ground.
PGND
Active Enable. Pulse high to enable high-power regulator output. Pulse low to disable regulator
output.
7
8
AE
Boost R
Select. Connect to system ground to select a boost R
of 0.5Ifor typical
DS-ON
DS-ON
SEL2
applications.
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.
9
SEL1
10
11
REG
LCE
Regulator Output. Connect to load circuit. Bypass to system ground with a 1FF (typ) capacitor.
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.
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.
12
PCKP
EP
—
Exposed Pad. Connect to GND.
Maxim Integrated
7
MAX17710
Energy-Harvesting Charger and Protector
Block Diagram
BATT
PCKP
UNREGULATED
OUTPUT
10µF
LINEAR CHARGE
AND IDEAL
DIODE CONTROL
OVERDISCHARGE
AND UNDERVOLTAGE
PROTECTION
THINERGY
MEC101
MAX17710
REF
CHG
0.1µF
RF, SOLAR,
OR OTHER
HIGH-VOLTAGE
SOURCE
LOAD V
1.0µF
DD
OUTPUT
LINEAR REG
REG
5.3V SHUNT
PROTECTION
TO REJECT
ZLLS410TA
3.3V/2.3V/1.8V
SELECT
OVERCHARGE
SEL 1
BATT
1.5µH
LX
PGND
SEL2
DISABLE
47µF
AE
EVENT
DETECTOR
TEG, SOLAR,
OR OTHER
LOW-VOLTAGE
SOURCE
MECHANICAL, RF,
PIEZO, OR OTHER
STATE
MACHINE
BOOST REG
300kI
LOAD V
DD
FB
ON
THRESHOLD
LCE
MICROCONTROLLER
FB
GND
Maxim Integrated
8
MAX17710
Energy-Harvesting Charger and Protector
remains active after the removal of the charge voltage.
The state of this latch is off when initial power is applied
Detailed Description
to the BATT pin.
Operation
The MAX17710 controls two main functions related to man-
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.
agement 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 cir-
cuit 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 con-
nected 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 V
rises above
CHG
4.15V (V ) does the device initialize to full operation and
CE
allow discharging.
Charge-Regulator Operation
The device charges the cell from an external energy
source connected to the CHG pin. Whenever the volt-
age 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
In the application circuit example, the cell is charged by
several high-voltage harvest sources. Whenever either har-
vest 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.
rises above V , the input linear regulator turns on to limit
CE
the charging voltage to 4.125V and protects the cell from
overcharge. Also at this time, any UVLO is reset, allow-
ing the LDO to power the application load. This release
of the lockout is latched by CHG exceeding V
and
CE
LOAD V
DD
THINERGY
MEC101
REG
AE
BATT
1µF
SEL2
EVENT
DETECTOR
SEL1
CHG
MECHANICAL,
RF, PIEZO,
OR OTHER
0.22µF
MAX17710
LOAD V
DD
HIGH-VOLTAGE AC
CHARGING SOURCE
(SOLAR, PIEZO)
HIGH-VOLTAGE DC
CHARGING SOURCE
(SOLAR, PIEZO)
LX
FB
MICROCONTROLLER
LCE
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
driving FB below the FB
the boost circuit. The process repeats after the harvest
source capacitor is recharged.
threshold, which disables
Boost Regulator Operation
The device includes a simple boost regulator controller to
support energy harvesting from low-voltage solar or ther-
moelectric 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.
OFF
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 volt-
age on FB exceeds the FB
threshold. At this time, the
ON
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 volt-
ages between 1.0V and 2.0V, additional components
are required. See the FB Divider section for a detailed
description.
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 V
, charge is delivered to
BATT
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,
LOAD V
DD
THINERGY
MEC101
REG
BATT
SEL2
1µF
SEL1
CHG
EVENT
DETECTOR
0.1µF
AE
MECHANICAL,
RF, PIEZO,
OR OTHER
ZLLS410TA
HIGH-SPEED
SCHOTTKY
MAX17710
LOAD V
DD
1.5µH
LX
FB
47µF
SOLAR CELL 2
SOLAR CELL 1
300kI
MICROCONTROLLER
LCE
GND EP PGND 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.
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.
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 maxi-
mum current rating of the LX pin from being exceeded.
Minimum inductor value is calculated as follows:
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.
LX inductor = V
x t
/LX
= 1.0V x
FB-ON
BOOST-ON
IMAX
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 volt-
age rise at 6.0V or lower when the LX driver turns off.
The LX pin can be damaged if the maximum voltage is
exceeded.
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 condi-
tions, 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
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 worst-
case conditions:
properly between the FB
boosting. The value for R2 is calculated as follows:
and FB
thresholds during
ON
OFF
V
= F
x (R1 + R2)/R1
HARVEST-ON
BON
R2 = (V
- 1.0V) x 500kI
HARVEST-ON
Source capacitor = (4.125V)2/(0.485V)2 x
CHG capacitor
where V
harvest source.
is the operational voltage of the
HARVEST-ON
Table 2. Boost Converter External Component Values
CHG
CAPACITOR
(µF)
MINIMUM LX
INDUCTOR
(µH)
RECOMMENDED
LX INDUCTOR
(µH)
MINIMUM
HARVEST SOURCE
CAPACITOR (µF)
RECOMMENDED
HARVEST SOURCE
CAPACITOR (µF)
APPLICATION
CHARGE SOURCE
High voltage
0.22
0.1
N/A
0.85
0.85
N/A
1.5
1.5
N/A
7.0
7.0
N/A
47
Low voltage < 10FW
Low voltage > 10FW
0.1
7.0
High voltage and low
voltage < 10FW
0.22
0.22
0.85
0.85
1.5
1.5
15.4
15.4
47
High voltage and low
voltage > 10FW
15.4
Maxim Integrated
11
MAX17710
Energy-Harvesting Charger and Protector
The C1 1nF capacitor acts as a voltage-level feed for-
ward to increase the responsiveness of the divider circuit
as the harvest source capacitor is discharged. The mini-
mum voltage is defined as:
CHG
0.1µF
V
~= V
- (FB
- FB
)
HARVEST-OFF
HARVEST-ON
ON
OFF
ZLLS410TA
L1
MAX17710
V
~= V
- 0.5V (typ)
HARVEST-OFF
HARVEST-ON
where V
source capacitor during boost.
is the lowest voltage of the harvest
HARVEST-OFF
1.0V TO 2.0V
CHARGE
SOURCE
LX
FB
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:
C1
1nF
R2
47µF
LX Inductor = V
V
x t
/LX
=
HARVEST-ON
HARVEST-ON
BOOST-ON
IMAX
R1
500kI
x (8.5 x 10-7)
All other components are selected as normal.
Energy-Harvesting Design Approaches
When designing an optimal energy harvest system,
there are three types of design approaches: linear har-
vest, 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 sys-
tem 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 qui-
escent 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.
Figure 3. FB Divider Circuit to Improve Boost Efficiency for
Charge Sources Between 1.0V and 2.0V
MPPT
(MAX POWER
TRACKING)
BOOST HARVEST
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 opera-
tion. 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 start-
ing up or disabling the regulator when active if the cell
becomes overdischarged.
POWER FROM HARVEST SOURCE
Figure 4. Energy-Harvesting Modes of Operation vs. Charge
Efficiency
Maxim Integrated
12
MAX17710
Energy-Harvesting Charger and Protector
The LDO becomes active when the AE pin is pulsed
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.
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.
Cell Undervoltage Lockout (UVLO)
If the cell and PCKP capacitance cannot provide sus-
tained support for the load, then the voltage at PCKP col-
lapses. 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
Once in high-current mode, the AE pin can remain logic-
high 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 high-
current 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
charge source has been connected to the system (V
> 4.15V). Figure 6 shows the UVLO protection modes.
CHG
Connecting any load to REG or PCKP instead of connect-
ing directly to the cell is highly recommended. This con-
trols 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
AE PULSED LOW
I
= 1nA (typ)
QBATT
AE PULSED HIGH
LCE PULSED
HIGH
AE PULSED
LOW
STARTUP
SUCCESS
> 3.7V
STARTUP
AE REGULATOR
ACTIVE
AE AND LCE
REGULATORS ACTIVE
LCE REGULATOR
ACTIVE
PCKP ON
REG OFF
= PCKP CAPACITOR
CHARGE CURRENT
+ 725nA (typ)
V
PCKP
CHARGE
DETECTED
LCE PULSED
LOW
AE PULSED
HIGH
PCKP ON
REG ON
PCKP ON
REG ON
PCKP ON
REG ON
I
QBATT
VCHG > VCE
I
= 725nA (typ)
I
= 875nA (typ)
I
= 150nA (typ)
QBATT
QBATT
QBATT
STARTUP FAIL
< 2.15V
CELL UNDERVOLTAGE
V
PCKP
V
V
< 2.15V (HIGH-CURRENT MODE)
< 3.0V (LOW-CURRENT MODE)
AFTER 500µs
AFTER 5s
PCKP
PCKP
UNDERVOLTAGE
LOCKOUT
PCKP OFF
REG OFF
I
= 1nA (typ)
QBATT
POWER-ON RESET (POR)
Figure 5. Regulator Output State Diagram
Maxim Integrated
13
MAX17710
Energy-Harvesting Charger and Protector
4.1V
2.15V
0V
BATT
PCKP
4.1V
2.15V
0V
BATT
4.1V
0V
4.1V
3.7V
PCKP
AE
0V
V
OH-AE
V
OH-AE
AE
V
OL-AE
V
OL-AE
3.3V
0V
REG
UVLO
0V
> t
UVLO1
(5s typ)
a. NORMAL REGULATOR OUTPUT ENABLE SEQUENCE
b. REGULATOR OUTPUT ENABLE FAIL DUE TO UVLO TIMEOUT
4.1V
BATT
PCKP
2.15V
0V
4.1V
3.0V
BATT
PCKP
4.1V
0V
2.15V
0V
3.3V
0V
3.3V
0V
REG
REG
> t
UVLO2
(500µs typ)
4.1V
0V
UVLO
0V
UVLO
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 reg-
ulator must be disabled and then reenabled. See Table 3.
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 fea-
tures, 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.
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:
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 follow-
ing equation:
U During startup, when there is an inrush current due to
the application’s load and capacitance.
C
PCKP
= I
x t
/(3.7 - V
)
TASK
TASK
MIN
U When the cell is cold (such as -40NC), and due to
increased cell resistance, it is unable to support high-
load currents.
where:
I
t
is the current required to sustain a required task,
TASK
TASK
is the time duration of the task, and V
is the
U If the system requires a load current higher than can be
supported by the cell alone.
MIN
minimum voltage of the load doing the task.
This equation assumes that the BATT impedance is high
and cannot support the load.
The device provides cell undervoltage protection by
limiting the current from BATT to PCKP and guarantee-
ing that the cell voltage does not fall below 2.15V. In
Table 3. Regulator Output Voltage Selection
SEL1 PIN CONNECTION
Connect to BATT
Open circuit
REG PIN OUTPUT VOLTAGE (V)
1.8
3.3
2.3
Connect to GND
Table 4. PCKP Pin Capacitor Values by Application
V
t
(ms)
I
(mA)
C
(µF)*
MIN
TASK
TASK
PCKP
3.0
3.0
2.8
2.8
2.3
2.3
5
8
100
5
5
5
5
5
4
5
50
28
14
18
36
2.5
5
10
*Capacitance value tolerances need to be considered.
Maxim Integrated
15
MAX17710
Energy-Harvesting Charger and Protector
Package Information
Ordering Information
For the latest package outline information and land patterns (foot-
prints), 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.
PART
TEMP RANGE
-40NC to +85NC
-40NC to +85NC
-40NC to +85NC
-40NC to +85NC
PIN-PACKAGE
12 UTDFN-EP**
12 UTDFN-EP**
12 UTDFN-EP**
12 UTDFN-EP**
MAX17710G+T*
MAX17710G+U*
MAX17710GB+
MAX17710GB+T
+Denotes a lead(Pb)-free/RoHS-compliant package.
U = Signifies tape cut.
PACKAGE
TYPE
PACKAGE OUTLINE
LAND
PATTERN NO.
CODE
NO.
12 UTDFN-EP V1233N+1
21-0451
90-0339
T = Tape and reel.
*Not recommended for new designs.
**EP = Exposed pad.
Maxim Integrated
16
MAX17710
Energy-Harvesting Charger and Protector
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
DESCRIPTION
0
12/12
Initial release
—
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
17
©
2012 Maxim Integrated Products, Inc.
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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