TI BQ25504

bq25504
SLUSAH0 – OCTOBER 2011
www.ti.com
Ultra Low Power Boost Converter with Battery Management for Energy Harvester
Applications
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FEATURES
1
•
•
•
•
Ultra Low Power With High Efficiency DC/DC
Boost Converter/Charger
– Continuous Energy Harvesting From Low
Input Sources: VIN ≥ 80 mV(Typical)
– Ultra Low Quiescent Current: IQ < 330 nA
(Typical)
– Cold-Start Voltage: VIN ≥ 330 mV (Typical)
Programmable Dynamic Maximum Power Point
Tracking (MPPT)
– Integrated Dynamic Maximum Power Point
Tracking for Optimal Energy Extraction
From a Variety of Energy Generation
Sources
– Input Voltage Regulation Prevents
Collapsing Input Source
Energy Storage
– Energy can be Stored to Re-Chargeable
Li-ion Batteries, Thin-film Batteries,
Super-Capacitors, or Conventional
Capacitors
Battery Charging and Protection
– User Programmable Undervoltage /
Overvoltage Levels
– On-Chip Temperature Sensor with
Programmable Overtemperature Shutoff
•
Battery Status Output
– Battery Good Output Pin
– Programmable Threshold and Hysteresis
– Warn Attached Microcontrollers of Pending
Loss of Power
– Can be Used to Enable/Disable System
Loads
APPLICATIONS
•
•
•
•
•
•
•
•
•
•
Energy Harvesting
Solar Charger
Thermal Electric Generator (TEG) Harvesting
Wireless Sensor Networks (WSN)
Industrial Monitoring
Environmental Monitoring
Bridge / Structural Health Monitoring (SHM)
Smart Building Controls
Portable and Wearable Health Devices
Entertainment System Remote Controls
LBST
CSTOR
Battery
CHVR
Solar
Cell
SYSTEM
LOAD
VSTOR
+
-
16
15
LBST
VSTOR
1
VSS
2
VIN_DC
`
14
13
VBAT
VSS
AVSS
12
VBAT_OK
11
bq25504
ROC 2
ROC 1
VBAT_OK
3
VOC_SAMP
OK_PROG
10
4
VREF_SAMP
OK_HYST
9
CREF
ROK1
ROK2
OT_PROG VBAT_OV VRDIV VBAT _UV
5
6
7
ROK3
8
ROV2
RUV 2
ROV1
RUV 1
DESCRIPTION
The bq25504 is the first of a new family of intelligent integrated energy harvesting Nano-Power management
solutions that are well suited for meeting the special needs of ultra low power applications. The product is
specifically designed to efficiently acquire and manage the microwatts (µW) to miliwatts (mW) of power
generated from a variety of DC sources like photovoltaic (solar) or thermal electric generators. The bq25504 is
the first device of its kind to implement a highly efficient boost converter/charger targeted toward products and
systems, such as wireless sensor networks (WSN) which have stringent power and operational demands. The
design of the bq25504 starts with a DCDC boost converter/charger that requires only microwatts of power to
begin operating.
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2011, Texas Instruments Incorporated
bq25504
SLUSAH0 – OCTOBER 2011
www.ti.com
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
DESCRIPTION CONTINUED
Once started, the boost converter/charger can effectively extract power from low voltage output harvesters such
as thermoelectric generators (TEGs) or single or dual cell solar panels. The boost converter can be started with
VIN as low as 330 mV, and once started, can continue to harvest energy down to VIN = 80 mV.
The bq25504 also implements a programmable maximum power point tracking sampling network to optimize the
transfer of power into the device. Sampling the VIN_DC open circuit voltage is programmed using external
resistors, and held with an external capacitor (CREF).
For example solar cells that operate at maximum power point (MPP) of 80% of their open circuit voltage, the
resistor divider can be set to 80% of the VIN_DC voltage and the network will control the VIN_DC to operate
near that sampled reference voltage. Alternatively, an external reference voltage can be provide by a MCU to
produce a more complex MPPT algorithm.
The bq25504 was designed with the flexibility to support a variety of energy storage elements. The availability of
the sources from which harvesters extract their energy can often be sporadic or time-varying. Systems will
typically need some type of energy storage element, such as a re-chargeable battery, super capacitor, or
conventional capacitor. The storage element will make certain constant power is available when needed for the
systems. The storage element also allows the system to handle any peak currents that can not directly come
from the input source.
To prevent damage to a customer’s storage element, both maximum and minimum voltages are monitored
against the user programmed undervoltage (UV) and overvoltage (OV) levels.
To further assist users in the strict management of their energy budgets, the bq25504 toggles the battery good
flag to signal an attached microprocessor when the voltage on an energy storage battery or capacitor has
dropped below a pre-set critical level. This should trigger the shedding of load currents to prevent the system
from entering an undervoltage condition. The OV, UV and battery good thresholds are programmed
independently.
All the capabilities of bq25504 are packed into a small foot-print 16-lead 3 mm x 3 mm QFN package.
ORDERING INFORMATION
(1)
PART NO.
PACKAGE
bq25504
QFN 16 pin 3 mm x 3 mm
ORDERING NUMBER
(TAPE AND REEL) (1)
PACKAGE
MARKING
QUANTITY
BQ25504RGTR
B5504
3000
BQ25504RGTT
B5504
250
The RGW package is available in tape on reel. Add R suffix to order quantities of 3000 parts per reel, T suffix for 250 parts per reel.
ABSOLUTE MAXIMUM RATINGS (1)
over operating free-air temperature range (unless otherwise noted)
VALUE
Input voltage
Peak Input Power, PIN_PK
VIN_DC, VOC_SAMP, VREF_SAMP, VBAT_OV, VBAT_UV, VRDIV,
OK_HYST, OK_PROG, VBAT_OK, VBAT, VSTOR, LBST (2)
UNIT
MIN
MAX
–0.3
5.5
V
400
mW
Operating junction temperature range, TJ
–40
125
°C
Storage temperature range, TSTG
–65
150
°C
(1)
(2)
2
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 under “recommended operating
conditions” is not implied. Exposure to absolute–maximum–rated conditions for extended periods may affect device reliability.
All voltage values are with respect to VSS/ground terminal.
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THERMAL INFORMATION
bq25504
THERMAL METRIC (1) (2)
θJA
Junction-to-ambient thermal resistance
48.5
θJCtop
Junction-to-case (top) thermal resistance
63.9
θJB
Junction-to-board thermal resistance
22
ψJT
Junction-to-top characterization parameter
1.8
ψJB
Junction-to-board characterization parameter
22
θJCbot
Junction-to-case (bottom) thermal resistance
6.5
(1)
(2)
UNITS
RGT (16 PINS)
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
For thermal estimates of this device based on PCB copper area, see the TI PCB Thermal Calculator.
RECOMMENDED OPERATING CONDITIONS
MIN
DC input voltage into VIN_DC (1)
VIN (DC)
NOM
0.13
(2)
MAX
UNIT
3
VBAT
Battery voltage range
5.25
V
CHVR
Input capacitance
4.23
4.7
5.17
µF
CSTOR
Storage capacitance
4.23
4.7
5.17
µF
CBAT
Battery pin capacitance or equivalent battery capacity
100
CREF
Sampled reference storage capacitance
9
10
11
nF
ROC1 + ROC2
Total resistance for setting for MPPT reference.
18
20
22
MΩ
ROK1 + ROK2 + ROK3
Total resistance for setting reference voltage.
9
10
11
MΩ
RUV1 + RUV2
Total resistance for setting reference voltage.
9
10
11
MΩ
ROV1 + ROV2
Total resistance for setting reference voltage.
9
10
11
MΩ
LBST
Input inductance
19.8
22
24.2
µH
TA
Operating free air ambient temperature
–40
85
°C
TJ
Operating junction temperature
–40
105
°C
(1)
(2)
2.5
V
µF
Maximum input power ≤ 300 mW. Cold start has been completed
VBAT_OV setting must be higher than VIN_DC
ELECTRICAL CHARACTERISTICS
Over recommended temperature range, typical values are at TA = 25°C. Unless otherwise noted, specifications apply for
conditions of VIN_DC = 1.2V, VBAT = VSTOR = 3V. External components LBST = 22 µH, CHVR = 4.7 µF CSTOR= 4.7 µF.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
3000
mV
BOOST CONVERTER \ CHARGER STAGE
VIN (DC)
DC input voltage into VIN_DC
Cold-start completed
IIN (DC)
Peak Current flowing from VIN into VIN_DC input
0.5V < VIN < 3 V; VSTOR = 4.2 V
PIN
Input power range for normal charging
VBAT > VIN_DC; VIN_DC = 0.5 V
VINCS
Cold-start Voltage. Input voltage that will start
charging of VSTOR
VBAT < VBAT_UV; VSTOR = 0 V;
0°C < TA < 85°C
PIN CS
Minimum cold-start input power to start normal
charging
VBAT < VBAT_UV; VSTOR = 0 V; Input source
impedance 0 Ω
VSTOR_CHGEN
Voltage on VSTOR when cold start operation ends
and normal charger operation begins
RBAT(on)
Resistance of switch between VBAT and VSTOR
when turned on.
130
200
300
mA
300
mW
330
450
mV
10
50
µW
1.77
1.95
V
VBAT = 4.2 V; VSTOR load = 50 mA
2
Ω
VBAT = 2.1 V
2
VBAT = 4.2 V
2
VBAT = 2.1 V
5
VBAT = 4.2 V
5
0.01
1.6
Charger Low Side switch ON resistance
RDS(on)
Charger rectifier High Side switch ON resistance
fSW_BST
Boost converter mode switching frequency
1
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Ω
Ω
MHz
3
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SLUSAH0 – OCTOBER 2011
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ELECTRICAL CHARACTERISTICS (continued)
Over recommended temperature range, typical values are at TA = 25°C. Unless otherwise noted, specifications apply for
conditions of VIN_DC = 1.2V, VBAT = VSTOR = 3V. External components LBST = 22 µH, CHVR = 4.7 µF CSTOR= 4.7 µF.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
1
5
nA
80
nA
BATTERY MANAGEMENT
VBAT = 2.1 V; VBAT_UV = 2.3 V, TJ = 25°C
VSTOR = 0 V
I(VBAT)
Leakage on VBAT pin
VBAT = 2.1 V; VBAT_UV = 2.3 V,
–40°C < TJ < 65°C, VSTOR = 0 V
VSTOR Quiescent current Charger Shutdown in UV
Condition
VIN_DC = 0V;
VBAT < VBAT_UV = 2.4V;
VSTOR = 2.2V, No load on VBAT
330
750
nA
VSTOR Quiescent current Charger Shutdown in OV
Condition
VIN_DC = 0V,
VBAT > VBAT_OV, VSTOR = 4.25,
No load on VBAT
570
1400
nA
VBAT_OV
Programmable voltage range for overvoltage
threshold (Battery voltage is rising)
VBAT increasing
2.5
5.25
V
VBAT_OV_HYST
Battery voltage overvoltage hysteresis threshold
(Battery voltage is falling), internal threshold
VBAT decreasing
18
VBAT_UV
Programmable voltage range for under voltage
threshold (Battery voltage is falling)
VBAT decreasing; VBAT_UV > VBias
2.2
VBAT_UV_HYST
Battery under voltage threshold hysteresis, internal
thershold
VBAT increasing
40
VBAT_OK
Programmable voltage range for threshold voltage
for high to low transition of digital signal indicating
battery is OK,
VBAT decreasing
VBAT_OK_HYST
Programmable voltage range for threshold voltage
for low to high transition of digital signal indicating
battery is OK,
VBAT increasing
VBAT_ACCURACY
Overall Accuracy for threshold values, UV, OV,
VBAT_OK
Selected resistors are 0.1% tolerance
VBAT_OKH
VBAT OK (High) threshold voltage
Load = 10 µA
VBAT_OKL
VBAT OK (Low) threshold voltage
Load = 10 µA
TSD_PROTL
The temperature at which the boost converter is
disabled and the switch between VBAT and VSTOR
is disconnected to protect the battery
OT_Prog = LO
65
OT_Prog = HI
120
I(VSTOR)
TSD_PROTH
Voltage for OT_PROG High setting
35
89
VBAT_OV
80
125
mV
V
mV
VBAT_UV
VBAT_OV
V
50
VBAT_OVVBAT_UV
mV
–5%
5%
VSTOR200mV
100
V
mV
°C
2
V
OT_Prog
Voltage for OT_PROG Low setting
0.3
V
BIAS and MPPT CONTROL STAGE
VOC_sample
Sampling period of VIN_DC open circuit voltage
16
s
VOC_Settling
Sampling period of VIN_DC open circuit voltage
256
ms
VIN_Reg
Regulation of VIN_DC during charging
VIN_shutoff
DC input voltage into VIN_DC when charger is
turned off
MPPT_Disable
Threshold on VOC_SAMP to disable MPPT
functionality
VBIAS
Voltage node which is used as reference for the
programmable voltage thresholds
4
0.5 V <VIN < 3 V; IIN (DC) = 10 mA
–10%
40
10%
80
130
VSTOR-15
mV
VIN_DC ≥ 0.5V; VSTOR ≥ 1.8 V
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1.21
mV
V
1.25
1.27
V
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DEVICE INFORMATION
RGT PACKAGE
(TOP VIEW)
16
15
LBST
VSTOR
`
14
13
VBAT
VSS
1
VSS
2
VIN_DC
3
VOC_SAMP
OK_PROG
10
VREF_SAMP
OK_HYST
9
AVSS
12
VBAT_OK
11
bq25504
4
OT_PROG VBAT_OV VRDIV VBAT_UV
5
6
7
8
Figure 1. bq25504 3mm x 3mm QFN-16 Package
PIN FUNCTIONS
PIN
NO.
NAME
I/O TYPE
DESCRIPTION
1
VSS
Input
General ground connection for the device
2
VIN_DC
Input
DC voltage input from energy harvesters
3
VOC_SAMP
Input
Sampling pin for MPPT network. To disable MPPT, connect to VSTOR
4
VREF_SAMP
Input
Switched node for holding the reference set by resistors on VOC_SAMP for MPPT. When MPPT is
disabled, input for reference voltage
5
OT_PROG
Input
Digital Programming input for overtemperature threshold
6
VBAT_OV
Input
Resistor divider input for over voltage threshold
7
VRDIV
8
VBAT_UV
Input
Resistor divider input for under voltage threshold
9
OK_HYST
Input
Resistor divider input for VBAT_OK hysteresis threshold
10
OK_PROG
Input
Resistor divider input for VBAT_OK threshold
11
VBAT_OK
Output
Digital battery good indicator referenced to VSTOR pin
12
AVSS
Supply
Signal ground connection for the device
13
VSS
Supply
General ground connection for the device
14
VBAT
15
VSTOR
16
LBST
Output
I/O
Output
Input
Resistor divider biasing voltage.
Connection for storage elements
Connection for the system load, output of the boost converter
Inductor connection for the boost converter switching node
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TYPICAL APPLICATION CIRCUITS
VIN_DC = 1.2 V, CSTOR= 4.7 µF, LBST= 22 µH, CHVR= 4.7 µF, CREF= 10 nF, TSD_PROTL (65°C),
MPPT (VOC) = 80% VBAT_OV = 3.1 V, VBAT_UV = 2.2 V, VBAT_OK = 2.4 V, VBAT_OK_HYST = 2.8 V,
ROK1 = 4.42 MΩ, ROK2 = 4.22 MΩ, ROK3 = 1.43 MΩ, ROV1 = 5.9 MΩ, ROV2 = 4.02 MΩ,
RUV1= 5.6 MΩ, RUV2 = 4.42 MΩ, ROC1= 15.62 MΩ, ROC2 = 4.42 MΩ
LBST
CSTOR
4.7µF
Battery(>100µF)
22µH
Solar
Cell
+
VSTOR
CHVR
4.7µF
1
-
16
15
LBST
VSTOR
`
14
13
VBAT
VSS
VSS
AVSS
12
VBAT_OK
2
ROC2
VIN_DC
11
ROK1
bq25504
4.42 MΩ
ROC 1
15.62MΩ
VBAT_OK
3
VOC_SAMP
4
VREF_SAMP
OK_PROG
CREF
0.01µF
OK_HYST
10
9
6
7
ROV2
4.02MΩ
ROV1
5.90MΩ
ROK2
4.22 MΩ
ROK3
OT_PROG VBAT_OV VRDIV VBAT _UV
5
4.42 MΩ
8
1.43MΩ
RUV2
4.42 MΩ
RUV 1
5.60 MΩ
Figure 2. Typical Solar Application Circuit
6
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VIN_DC = 0.5 V, CSTOR = 4.7 µF, LBST = 22 µH, CHVR = 4.7 µF, CREF = 10 nF, TSD_PROTH (120°C),
MPPT (VOC) = 50% VBAT_OV = 4.2 V, VBAT_UV = 3.2 V, VBAT_OK = 3.5 V, VBAT_OK_HYST = 3.7 V,
ROK1 = 3.32 MΩ, ROK2 = 6.12 MΩ, ROK3 = 0.542 MΩ, ROV1 = 4.42 MΩ, ROV2 = 5.62 MΩ,
RUV1 = 3.83 MΩ, RUV2 = 6.12 MΩ, ROC1 = 10 MΩ, ROC2 = 10 MΩ
LBST
CSTOR
4.7µF
Battery(>100µF)
22µH
VSTOR
CHVR
4.7µF
1
16
15
LBST
VSTOR
`
14
13
VBAT
VSS
VSS
AVSS
12
VBAT_OK
Thermo electric
generator
2
ROC 2
10 MΩ
11
ROK1
bq25504
10 MΩ
ROC 1
VBAT_OK
VIN_DC
3
VOC_SAMP
4
VREF _SAMP
OK_PROG
CREF
0.01µF
OK_HYST
10
9
6
7
ROK2
6.12 MΩ
ROK3
OT_PROG VBAT_OV VRDIV VBAT _UV
5
3.32 MΩ
8
542kΩ
VSTOR
ROV2
5.62MΩ
ROV1
4.42MΩ
RUV 2
6.12MΩ
RUV 1
3.83MΩ
Figure 3. Typical TEG Application Circuit
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VIN_DC = 1.2 V, CSTOR = 4.7 µF, LBST = 22 µH, CHVR = 4.7 µF, TSD_PROTL (65°C),
MPPT (VOC) = Disabled VBAT_OV = 3.3 V, VBAT_UV = 2.2 V, VBAT_OK = 2.8 V, VBAT_OK_HYST = 3.1 V,
ROK1 = 3.97 MΩ, ROK2 = 5.05 MΩ, ROK3 = 0.976 MΩ, ROV1 = 5.56 MΩ,
ROV2 = 4.48 MΩ, RUV1 = 5.56 MΩ, RUV2 = 4.42 MΩ
LBST
CSTOR
4.7 µF
Primary Cell
Battery(>100 µF)
22 µH
VSTOR
CHVR
4. 7 µF
1
16
15
LBST
VSTOR
`
14
13
VBAT
VSS
VSS
12
AVSS
VBAT_OK
2
VBAT_OK
VIN_DC
11
ROK1
bq25504
VSTOR
3
VOC_SAMP
4
VREF_SAMP
3.97 MΩ
OK_PROG
OK_HYST
10
9
OT_PROG VBAT_OV VRDIV VBAT _UV
5
6
7
ROV2
4.48 MΩ
ROV1
5.56 MΩ
8
ROK2
5.05 MΩ
ROK3
976 kΩ
RUV2
4.42 MΩ
RUV1
5.56 MΩ
Figure 4. Typical MPPT Disabled Application Circuit
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HIGH-LEVEL FUNCTIONAL BLOCK DIAGRAM
LBST
VSTOR
VBAT
VSS
Boost Charge
Controller
AVSS
VSS
Cold-Start
Unit
VIN_DC
Enable
Enable
VBAT_OK
Interrupt
VOC_SAMP
OK_PROG
BAT_SAVE
MPPT
Controller
Vref
VREF_SAMP
OT
Battery Threshold
Control
OK
OK_HYST
UV
OV
Temperature
Sensing
Element
Vref
Bias Reference
and Oscillator
Vref
OT_PROG VBAT_OV
VRDIV
VBAT_UV
Figure 5. High-level Functional Diagram
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TYPICAL CHARACTERISTICS
Spacer
100
100
IIN = 10µA
90
80
80
70
70
Efficiency (%)
Efficiency (%)
90
60
50
40
30
60
50
40
30
20
VSTOR = 1.8V
VSTOR = 3V
VSTOR = 5.5V
10
0
−10
IIN = 100µA
VSTOR = 3.3 V
VSTOR = 1.8 V
VSTOR = 5.5 V
20
10
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3
Input Voltage (V)
G001
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3
Input Voltage (V)
G002
Figure 6. Efficiency vs Input Voltage
Figure 7. Efficiency vs Input Voltage
100
100
IIN = 10mA
VIN = 2V
90
90
Efficiency (%)
Efficiency (%)
80
70
60
50
40
VSTOR = 3V
VSTOR = 1.8V
VSTOR = 5.5V
30
20
80
70
60
VSTOR = 3V
VSTOR = 1.8V
VSTOR = 5.5V
50
40
0.01
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3
Input Voltage (V)
G003
Figure 8. Efficiency vs Input Voltage
0.1
1
Input Current (mA)
10
100
G004
Figure 9. Efficiency vs Input Current
90
90
VIN = 1V
VIN = 0.5V
80
80
Efficiency (%)
Efficiency (%)
70
70
60
60
50
40
50
40
0.01
0.1
1
Input Current (mA)
VSTOR = 3V
VSTOR = 1.8V
VSTOR = 5.5V
30
10
20
0.01
100
G005
Figure 10. Efficiency vs Input Current
10
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VSTOR = 3V
VSTOR = 1.8V
VSTOR = 5.5V
0.1
1
Input Current (mA)
10
100
G006
Figure 11. Efficiency vs Input Current
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TYPICAL CHARACTERISTICS (continued)
80
1000
VIN = 0.2V
900
800
VSTOR Current (nA)
Efficiency (%)
70
60
50
40
VSTOR = 3V
VSTOR = 1.8V
VSTOR = 5.5V
30
20
0.01
0.1
1
Input Current (mA)
10
700
600
500
400
300
VSTOR = 1.8V
VSTOR = 3V
VSTOR = 4V
200
100
0
−60
100
G007
Figure 12. Efficiency vs Input Current
−40
−20
0
20
40
60
Temperature (°C)
80
100
120
G008
Figure 13. VSTOR Quiescent Current vs Temperature
24
400
22
350
Time (ms)
Time (s)
20
18
16
300
250
14
200
12
10
−50−40−30−20−10 0 10 20 30 40 50 60 70 80 90 100
Temperature (°C)
G009
150
−50−40−30−20−10 0 10 20 30 40 50 60 70 80 90 100
Temperature (°C)
G010
Figure 14. Sample Period vs Temperature
Figure 15. Settling Period vs Temperature
VIN = 1 V, RIN = 20 W, VBAT = ramping power supply
VIN = 1 V, RIN = 20 W, VBAT = 100 µF capacitor
Figure 16. Example of Startup with no Battery and
10 KΩ Load
Figure 17. Example of VBAT_OK Operation, Ramping
Battery From 0 V to 3.1 V
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TYPICAL CHARACTERISTICS (continued)
VIN = 1 V, RIN = 20 W, VBAT = 3.1 V, RBAT = 100 mW
VIN = 1 V, RIN = 20 W, VBAT = 2.5 V, RBAT = 100 mW
Figure 18. Example of PFM Switching Converter Waveform
VIN = 1 V, RIN = 20 W, VBAT = 1.9 V, RBAT = 100 mW
VIN = 1 V, RIN = 20 W, VBAT = 3 V, RBAT = 100 mW
Figure 20. Example of Startup When VBAT is Held
Below UV Setting
12
Figure 19. Example of Output Ripple Voltage During
Operation at O V Setting
Figure 21. Example of Sampling Time for MPPT Operation
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DETAILED PRINCIPLE OF OPERATION
OPERATION
The bq25504 is an ultra low quiescent current, efficient synchronous boost converter/charger. The boost
converter is based on a switching regulator architecture which maximizes efficient operation while minimizing
start-up and operation power. The bq25504 uses pulse frequency mode (PFM) modulation to maintain efficiency,
even under light load conditions. In addition, bq25504 also implements battery protection features so that either
rechargeable batteries or capacitors can be used as energy storage elements. Figure 5 is a high-level functional
block diagram which highlights most of the major functional blocks inside the bq25504.
Boost Converter / Charger
Operation of the boost converter / charger begins when there is sufficient power available at the input pin
(VIN_DC) or available from an attached battery (VBAT) to raise the voltage at pin VSTOR above 1.8 V. The
start-up below 1.8 V on VSTOR of the boost-converter begins with the Cold-Start sub-system. If the VIN_DC is
greater than VSTOR or VBAT then current may flow until the voltage at the input is reduced or the voltage at
VSTOR and VBAT rise. This is considered an abnormal condition and the boost converter/charger does not
operate.
Cold -Start
The cold-start subsystem is used to turn on the device when the voltage present on pin VSTOR is < 1.8 V. Inside
the IC there is a switch (PMOS) between the energy storage capacitor VSTOR and the battery. If a battery is
initially attached to pin VBAT, the PMOS switch is momentary closed and any available charge from the battery
can be dumped onto VSTOR. If the resulting voltage is greater than about 1.8 V, then the bq25504’s biasing and
oscillator circuits can be turned on, and start up of the boost converter will be initiated. However, if there is
insufficient energy available in a connected battery, then the PMOS circuit is opened after ~20 ms, and the
cold-start sequence is initiated via power provided by power at the VIN_DC input pin.
When the voltage at pin VIN_DC exceeds the minimum input voltage with sufficient power, the cold start
subsystem turns on. When the storage capacitor voltage reaches 1.8 V the main boost regulator starts up. The
cold-start circuitry is then turned off after the voltage condition of VSTOR >1.8V and ~32 ms after input power
was applied. The output of the main boost regulator is now compared against battery undervoltage threshold
(VBAT_UV). When the VBAT_UVLO threshold is reached, the PMOS switch is turned on, which allows the
energy storage element attached to VBAT to charge up. Figure 22 shows the key threshold voltages. The battery
management thresholds are explained later is this section. Cold start is not as efficient as the main boost
regulator. If there is not sufficient power available it is possible that the cold start continuously runs and the
VSTOR output does not increase to 1.8 V and start the main boost regulator.
Boost Converter/Charger Operation
The boost converter in bq25504 is used to charge the storage element attached at VBAT with the energy
available from the DC input source. It employs pulse frequency modulation (PFM) mode of control to regulate the
input voltage (VIN_DC) close to the desired reference voltage. The reference voltage is set by the MPPT control
scheme as described in the next section. Input voltage regulation is obtained by transferring charge from the
input to VSTOR only when the input voltage is higher than the voltage on pin VREF_SAMP. The current through
the inductor is controlled through internal current sense circuitry. The peak current in the inductor is dithered
internally to set levels to maintain high efficiency of the converter across a wide input current range. The
converter nominally transfers up to a typical peak of 200 mA of input current. The boost converter is disabled
when the voltage on VSTOR reaches the OV condition to protect the battery connected at VBAT from
overcharging.
Maximum Power Point Tracking
Maximum power point tracking (MPPT) is implemented in bq25504 in order to maximize the power extracted
from an energy harvester source. MPPT is performed by periodically sampling a ratio of the open-circuit voltage
of the energy harvester and using that as the reference voltage (VREF_SAMP) to the boost converter. The
sampling ratio can be externally programmed using the resistors ROC1 and ROC2. For solar harvesters, the
resistive division ratio can be typically set between 0.7-0.8 and for thermoelectric harvesters; a resistive division
ratio of 0.5 is typically used. The exact ratio for MPPT can be optimized to meet the needs of the input source
being used.
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Internally, the boost converter modulates the effective impedance of the energy transfer circuitry to regulate the
input voltage (VIN_DC) to the sampled reference voltage (VREF_SAMP). A new reference voltage is obtained
every 16s by periodically disabling the charger for 256ms and sampling a ratio of the open-circuit voltage. The
reference voltage is set by the following expression:
æ
ö
R OC1
VREF_SAMP = VIN_DC(OpenCircuit) ç
÷
è R OC1 + R OC2 ø
(1)
The internal MPPT circuitry and the periodic sampling of VIN_DC can be disabled by tying the VOC_SAMP pin
to VSTOR. When disabled an external reference voltage can be fed to the VREF_SAMP pin. The boost
converter will then regulate VIN_DC to the externally provided reference. If input regulation is not desired,
VREF_SAMP can be tied to GND.
Storage Element
The storage elements should be connected to VBAT pin. Many types of elements can be used, such as
capacitors, super capacitors or various battery chemistries. If a capacitor is selected it needs to meet the
minimum capacitance of 100 µF. If a battery is used it should be selected to have a minimum capacity equivalent
to 100 µF capacitance. To take full advantage of the battery management, the load is normally tied to the
VSTOR pin. Also, if there is large load transients or the storage element has impedance then it is necessary to
add a low ESR by-pass capacitor to prevent a droop in voltage.
Battery Management
In this section the battery management functionality of the bq25504 integrated circuit (IC) is presented. The IC
has internal circuitry to manage the voltage across the storage element and to optimize the charging of the
storage element. For successfully extracting energy from the source, three different threshold voltages must be
programmed using external resistors, namely the under voltage (UV) threshold, battery good threshold
(VBAT_OK) and over voltage (OV) threshold. The three threshold voltages determine the region of operation of
the IC. Figure 22 shows a plot of the voltage at the VSTOR pin and the various threshold voltages. For the best
operation of the system, the VBAT_OK should be used to determine when a load can be applied or removed. A
detailed description of the three voltage thresholds and the procedure for designing the external resistors for
setting the three voltage thresholds are described next.
device absolute max = 5.5 V
Charger off
over voltage (user programmable) = 3.1 V
Increasing VSTOR voltage
over voltage – hyst (internal)
VBAT_OK + hyst (user programmable) = 2.8 V
VBAT_OK (user programmable) = 2.4 V
Main Boost
Charger on
under voltage + hyst (internal)
under voltage (user programmable) = 2.2 V
charger enable = 1.8 V
chip enable = 1.4 V
Cold start
ground
Figure 22. Figure Shows the Relative Position of Various Threshold Voltages
(Threshold Voltages are From Typical Solar Application Circuit in Figure 2)
14
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Battery Undervoltage Protection
To prevent rechargeable batteries from being deeply discharged and damaged, and to prevent completely
depleting charge from a capacitive storage element, the undervoltage (VBAT_UV) threshold must be set using
external resistors. The VBAT_UV threshold voltage when the battery voltage is decreasing is given by
Equation 2:
æ
ö
R
VBAT_UV = VBIAS ç 1 + UV2 ÷
R UV1 ø
è
(2)
The sum of the resistors must be 10 MΩ i.e., RUV1 + RUV2 = 10 MΩ. The undervoltage threshold when battery
voltage is increasing is given by UV_HYST. It is internal set to the under voltage threshold plus an internal
hysteresis voltage denoted by VBAT_UV_HYST. For proper functioning of the IC and the overall system, the
load must be connected to the VSTOR pin while the storage element must be connected to the VBAT pin. Once
the VSTOR pin voltage goes above the UV_HYST threshold, the VSTOR pin and the VBAT pins are shorted.
The switch remains closed until the VSTOR pin voltage falls below the under voltage threshold. The VBAT_UV
threshold should be considered a fail safe to the system and the system load should be removed or reduced
based on the VBAT_OK signal.
Battery Overvoltage Protection
To prevent rechargeable batteries from being exposed to excessive charging voltages and to prevent over
charging a capacitive storage element, the over-voltage (VBAT_OV) threshold level must be set using external
resistors. This is also the voltage value to which the charger will regulate the VSTOR/VBAT pin when the input
has sufficient power. The VBAT_OV threshold when the battery voltage is rising is given by Equation 3:
æ
ö
R
3
VBAT_OV = VBIAS ç 1 + OV2 ÷
2
R OV 1 ø
è
(3)
The sum of the resistors must be 10 MΩ i.e. ROV1 + ROV2 = 10 MΩ. The overvoltage threshold when battery
voltage is decreasing is given by OV_HYST. It is internal set to the over voltage threshold minus an internal
hysteresis voltage denoted by VBAT_OV_HYST. Once the voltage at the battery exceeds VBAT_OV threshold,
the boost converter is disabled. The charger will start again once the battery voltage falls below the
VBAT_OV_HYST level. When there is excessive input energy, the VBAT pin voltage will ripple between the
VBAT_OV and the VBAT_OV_HYST levels.
CAUTION
It should also be noted that if VIN_DC is higher than VSTOR and VSTOR is higher
than VBAT_OV, the input VIN_DC is shorted to ground to stop further charging of the
attached battery or capacitor. It is critical that if this case is expected, the source
impedance on VIN_DC is made higher than 20 Ω, it must not be a low impedance
source.
Battery Voltage in Operating Range (VBAT_OK Output)
The IC allows the user to set a programmable voltage independent of the overvoltage and undervoltage settings
to indicate whether the battery voltage is at an acceptable level. When the battery voltage is decreasing the
threshold is by Equation 4
æ
ö
R
VBAT_OK_PROG = VBIAS ç 1 + O K2 ÷
R OK1 ø
è
(4)
When the battery voltage is increasing, the threshold is by Equation 5
æ
R
+ R O K3 ö
VBAT_OK_HYST = VBIAS ç 1 + OK2
÷
R O K1
è
ø
(5)
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The sum of the resistors must be 10 MΩ i.e., ROK1 + ROK2 + ROK3= 10 MΩ. The logic high level of this signal is
equal to the VSTOR voltage and the logic low level is ground. The logic high level has ~20 KΩ internally in series
to limit the available current to prevent MCU damage until it is fully powered. The VBAT_OK_PROG threshold
must be greater than or equal to the UV threshold. For the best operation of the system, the VBAT_OK should
be setup to determine when a load can be applied or removed to optimize the storage element capacity.
Thermal Shutdown
Rechargeable Li-ion batteries need protection from damage due to operation at elevated temperatures. The
application should provide this battery protection and ensure that the ambient temperature is never elevated
greater than the expected operational range of 85°C.
The bq25504 uses an integrated temperature sensor to monitor the junction temperature of the device. If the
OT_PROG pin is tied low then the temperature threshold for thermal protection is set to TSD_ProtL which is
65°C typically. If the OT_PROG is tied high, then the temperature is set to TSD_ProtH which is 120°C typically.
Once the temperature threshold is exceeded, the boost converter/charger is disabled and charging ceases. Once
the temperature of the device drops below this threshold, the boost converter/charger can resume operation. In
order to avoid unstable operation near the overtemp threshold, a built-in hysteresis of approximately 5°C has
been implemented. Care should be taken to not over discharge the battery in this condition since the boost
converter/charger is disabled. However, if the supply voltage drops to the VBAT_UV setting, then the switch
between VBAT and VSTOR will open and protect the battery even if the device is in thermal shutdown.
APPLICATION INFORMATION
INDUCTOR SELECTION
For the bq25504 to operate properly, an inductor of appropriate value must be connected between Pin # 16
(LBST) and Pin #2 (VIN_DC) for the boost converter.
For the boost converter / charger, the inductor must have an inductance = 22 µH and have a peak current
capability of ≥250 mA with the minimum series resistance to keep high efficiency.
CAPACITOR SELECTION
In general, all the capacitors need to be low leakage. Any leakage the capacitors have will reduce efficiency,
increase the quiescent current and diminish the effectiveness of the IC for energy harvesting.
Sampled Reference Storage Capacitance:
The MPPT operation depends on the sampled value of the open circuit voltage and the input regulation follows
the voltage stored on the CREF capacitor. This capacitor is very sensitive to leakage since the holding period is
around 16 seconds. As the capacitor voltage drops due to any leakage, the input regulation voltage will also drop
and this can prevent proper operation from extraction the maximum power from the input source. Therefore, it is
recommended that the leakage be less than 2 nA at 3 V bias.
Input capacitor:
Operation of the BQ25504 requires a capacitor to be connected between Pin 15 (VSTOR) and ground. A
capacitor of 4.7 µF should be connected between Pin 15 and ground to assure stability of the boost converter,
especially when the battery is fully charged and the converter in output voltage limiting mode.
Energy from the energy harvester input source is initially stored on a capacitor CHVR tied to Pin 2 (VIN_DC) and
ground (VSS, Pin 1). For energy harvesters which have a source impedance which is dominated by a capacitive
behavior, the value of the harvester capacitor should scaled according to the value of the output capacitance of
the energy source , but an initial value of 4.7 µF is recommended.
16
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Storage capacitor:
An additional storage capacitor CBAT, either stand-alone, or in parallel with the battery should be attached
between Pin 14 (VBAT) and GND. The value of this capacitor should be selected to meet the needs of any load
attached to the battery. For instance, some Li-ion batteries or thin-film batteries may not have the current
capacity to meet the surge current requirements of an attached low power radio. Therefore, adding a capacitor
may help buffer this load and provide the brief current surge needs.
Additionally, when the system load has large transients, adding a small high frequency capacitor in parallel to
CSTOR may help buffer this load and provide the brief current surge needs.
For a recommend list of standard components, please see the EVM User’s guide.
LAYOUT CONSIDERATIONS
As for all switching power supplies, the layout is an important step in the design, especially at high peak currents
and high switching frequencies. If the layout is not carefully done, the boost converter/charger could show
stability problems as well as EMI problems. Therefore, use wide and short traces for the main current path and
for the power ground paths. The input and output capacitor, as well as the inductor should be placed as close as
possible to the IC.
The resistors that program the thresholds should be placed as close as possible to the input pins of the IC to
minimize parasitic capacitance to less than 2 pF.
To layout the ground, it is recommended to use short traces as well, separated from the power ground traces.
This avoids ground shift problems, which can occur due to superimposition of power ground current and control
ground current. Assure that the ground traces are connected close to the device GND pin.
THERMAL CONSIDERATIONS
Implementation of integrated circuits in low-profile and fine-pitch surface-mount packages typically requires
special attention to power dissipation. Many system-dependent issues such as thermal coupling, airflow, added
heat sinks and convection surfaces, and the presence of other heat-generating components affect the
power-dissipation limits of a given component.
Three basic approaches for enhancing thermal performance are listed below.
• Improving the power-dissipation capability of the PCB design
• Improving the thermal coupling of the component to the PCB
• Introducing airflow in the system
For more details on how to use the thermal parameters in the Thermal Table, check the Thermal Characteristics
Application Note (SZZA017) and the IC Package Thermal Metrics Application Note (SPRA953).
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PACKAGE OPTION ADDENDUM
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17-Oct-2011
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package
Drawing
Pins
Package Qty
Eco Plan
(2)
Lead/
Ball Finish
MSL Peak Temp
(3)
BQ25504RGTR
ACTIVE
QFN
RGT
16
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
BQ25504RGTT
ACTIVE
QFN
RGT
16
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
Samples
(Requires Login)
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
14-Oct-2011
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
BQ25504RGTR
QFN
RGT
16
3000
330.0
12.4
3.3
3.3
1.1
8.0
12.0
Q2
BQ25504RGTT
QFN
RGT
16
250
180.0
12.4
3.3
3.3
1.1
8.0
12.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
14-Oct-2011
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
BQ25504RGTR
QFN
RGT
16
3000
346.0
346.0
29.0
BQ25504RGTT
QFN
RGT
16
250
210.0
185.0
35.0
Pack Materials-Page 2
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