Ultra Low Power Boost Converter with Battery Management ... · All the capabilities of bq25504 are packed into a small foot-print16-lead3 mm x 3 mm QFN package. ORDERING INFORMATION

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5 6 7 8

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16 15 14 13`

CHVR

LBST CSTOR

VSTOR

VBAT_OK

bq25504

Solar

Cell

+

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ROC1

ROC2

CREF

ROV1

ROV2

RUV1

RUV2

ROK1

ROK2

ROK3

BatterySYSTEM

LOAD

VSS

VIN_DC

AVSS

VOC_SAMP

VREF_SAMP

OT_PROG VBAT_OV VRDIV VBAT_UV

LBST VSTOR VBAT VSS

OK_HYST

OK_PROG

VBAT_OK

bq25504www.ti.com SLUSAH0 –OCTOBER 2011

Ultra Low Power Boost Converter with Battery Management for Energy HarvesterApplications

Check for Samples: bq25504

1FEATURES• Ultra Low Power With High Efficiency DC/DC • Battery Status Output

Boost Converter/Charger – Battery Good Output Pin– Continuous Energy Harvesting From Low – Programmable Threshold and Hysteresis

Input Sources: VIN ≥ 80 mV(Typical) – Warn Attached Microcontrollers of Pending– Ultra Low Quiescent Current: IQ < 330 nA Loss of Power

(Typical) – Can be Used to Enable/Disable System– Cold-Start Voltage: VIN ≥ 330 mV (Typical) Loads

• Programmable Dynamic Maximum Power PointTracking (MPPT) APPLICATIONS– Integrated Dynamic Maximum Power Point • Energy Harvesting

Tracking for Optimal Energy Extraction • Solar ChargerFrom a Variety of Energy Generation • Thermal Electric Generator (TEG) HarvestingSources

• Wireless Sensor Networks (WSN)– Input Voltage Regulation Prevents• Industrial MonitoringCollapsing Input Source• Environmental Monitoring• Energy Storage• Bridge / Structural Health Monitoring (SHM)– Energy can be Stored to Re-Chargeable• Smart Building ControlsLi-ion Batteries, Thin-film Batteries,

Super-Capacitors, or Conventional • Portable and Wearable Health DevicesCapacitors • Entertainment System Remote Controls

• Battery Charging and Protection– User Programmable Undervoltage /

Overvoltage Levels– On-Chip Temperature Sensor with

Programmable Overtemperature Shutoff

DESCRIPTIONThe bq25504 is the first of a new family of intelligent integrated energy harvesting Nano-Power managementsolutions that are well suited for meeting the special needs of ultra low power applications. The product isspecifically designed to efficiently acquire and manage the microwatts (µW) to miliwatts (mW) of powergenerated from a variety of DC sources like photovoltaic (solar) or thermal electric generators. The bq25504 isthe first device of its kind to implement a highly efficient boost converter/charger targeted toward products andsystems, such as wireless sensor networks (WSN) which have stringent power and operational demands. Thedesign of the bq25504 starts with a DCDC boost converter/charger that requires only microwatts of power tobegin operating.

1

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of TexasInstruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

PRODUCTION DATA information is current as of publication date. Copyright © 2011, Texas Instruments IncorporatedProducts conform to specifications per the terms of the TexasInstruments standard warranty. Production processing does notnecessarily include testing of all parameters.

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bq25504SLUSAH0 –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 foamduring storage or handling to prevent electrostatic damage to the MOS gates.

DESCRIPTION CONTINUEDOnce started, the boost converter/charger can effectively extract power from low voltage output harvesters suchas thermoelectric generators (TEGs) or single or dual cell solar panels. The boost converter can be started withVIN 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 thetransfer of power into the device. Sampling the VIN_DC open circuit voltage is programmed using externalresistors, 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, theresistor divider can be set to 80% of the VIN_DC voltage and the network will control the VIN_DC to operatenear that sampled reference voltage. Alternatively, an external reference voltage can be provide by a MCU toproduce a more complex MPPT algorithm.

The bq25504 was designed with the flexibility to support a variety of energy storage elements. The availability ofthe sources from which harvesters extract their energy can often be sporadic or time-varying. Systems willtypically need some type of energy storage element, such as a re-chargeable battery, super capacitor, orconventional capacitor. The storage element will make certain constant power is available when needed for thesystems. The storage element also allows the system to handle any peak currents that can not directly comefrom the input source.

To prevent damage to a customer’s storage element, both maximum and minimum voltages are monitoredagainst 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 goodflag to signal an attached microprocessor when the voltage on an energy storage battery or capacitor hasdropped below a pre-set critical level. This should trigger the shedding of load currents to prevent the systemfrom entering an undervoltage condition. The OV, UV and battery good thresholds are programmedindependently.

All the capabilities of bq25504 are packed into a small foot-print 16-lead 3 mm x 3 mm QFN package.

ORDERING INFORMATIONORDERING NUMBER PACKAGEPART NO. PACKAGE QUANTITY(TAPE AND REEL) (1) MARKING

BQ25504RGTR B5504 3000bq25504 QFN 16 pin 3 mm x 3 mm

BQ25504RGTT B5504 250

(1) 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)

VALUEUNIT

MIN MAX

Input voltage –0.3 5.5 VVIN_DC, VOC_SAMP, VREF_SAMP, VBAT_OV, VBAT_UV, VRDIV,OK_HYST, OK_PROG, VBAT_OK, VBAT, VSTOR, LBST (2)

Peak Input Power, PIN_PK 400 mW

Operating junction temperature range, TJ –40 125 °CStorage temperature range, TSTG –65 150 °C

(1) Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratingsonly and functional operation of the device at these or any other conditions beyond those indicated under “recommended operatingconditions” is not implied. Exposure to absolute–maximum–rated conditions for extended periods may affect device reliability.

(2) All voltage values are with respect to VSS/ground terminal.

2 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated

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THERMAL INFORMATIONbq25504

THERMAL METRIC (1) (2) UNITSRGT (16 PINS)

θJA Junction-to-ambient thermal resistance 48.5

θJCtop Junction-to-case (top) thermal resistance 63.9

θJB Junction-to-board thermal resistance 22°C/W

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) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.(2) For thermal estimates of this device based on PCB copper area, see the TI PCB Thermal Calculator.

RECOMMENDED OPERATING CONDITIONSMIN NOM MAX UNIT

VIN (DC) DC input voltage into VIN_DC (1) 0.13 3 V

VBAT Battery voltage range (2) 2.5 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 µF

CREF Sampled reference storage capacitance 9 10 11 nF

ROC1 + ROC2 Total resistance for setting for MPPT reference. 18 20 22 MΩROK1 + ROK2 + ROK3 Total resistance for setting reference voltage. 9 10 11 MΩRUV1 + RUV2 Total resistance for setting reference voltage. 9 10 11 MΩROV1 + ROV2 Total resistance for setting reference voltage. 9 10 11 MΩLBST Input inductance 19.8 22 24.2 µH

TA Operating free air ambient temperature –40 85 °CTJ Operating junction temperature –40 105 °C

(1) Maximum input power ≤ 300 mW. Cold start has been completed(2) VBAT_OV setting must be higher than VIN_DC

ELECTRICAL CHARACTERISTICSOver recommended temperature range, typical values are at TA = 25°C. Unless otherwise noted, specifications apply forconditions 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

BOOST CONVERTER \ CHARGER STAGE

VIN (DC) DC input voltage into VIN_DC Cold-start completed 130 3000 mV

IIN (DC) Peak Current flowing from VIN into VIN_DC input 0.5V < VIN < 3 V; VSTOR = 4.2 V 200 300 mA

PIN Input power range for normal charging VBAT > VIN_DC; VIN_DC = 0.5 V 0.01 300 mW

VBAT < VBAT_UV; VSTOR = 0 V;Cold-start Voltage. Input voltage that will startVINCS 330 450 mV

charging of VSTOR 0°C < TA < 85°C

Minimum cold-start input power to start normal VBAT < VBAT_UV; VSTOR = 0 V; Input sourcePIN CS 10 50 µW

charging impedance 0 Ω

Voltage on VSTOR when cold start operation endsVSTOR_CHGEN 1.6 1.77 1.95 V

and normal charger operation begins

Resistance of switch between VBAT and VSTORRBAT(on) VBAT = 4.2 V; VSTOR load = 50 mA 2 Ω

when turned on.

VBAT = 2.1 V 2Charger Low Side switch ON resistance Ω

VBAT = 4.2 V 2RDS(on)

VBAT = 2.1 V 5Charger rectifier High Side switch ON resistance Ω

VBAT = 4.2 V 5

fSW_BST Boost converter mode switching frequency 1 MHz

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ELECTRICAL CHARACTERISTICS (continued)Over recommended temperature range, typical values are at TA = 25°C. Unless otherwise noted, specifications apply forconditions 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

BATTERY MANAGEMENT

VBAT = 2.1 V; VBAT_UV = 2.3 V, TJ = 25°C1 5 nA

VSTOR = 0 VI(VBAT) Leakage on VBAT pin

VBAT = 2.1 V; VBAT_UV = 2.3 V,80 nA

–40°C < TJ < 65°C, VSTOR = 0 V

VIN_DC = 0V;VSTOR Quiescent current Charger Shutdown in UV

VBAT < VBAT_UV = 2.4V; 330 750 nACondition

VSTOR = 2.2V, No load on VBATI(VSTOR)

VIN_DC = 0V,VSTOR Quiescent current Charger Shutdown in OV

VBAT > VBAT_OV, VSTOR = 4.25, 570 1400 nACondition

No load on VBAT

Programmable voltage range for overvoltageVBAT_OV VBAT increasing 2.5 5.25 V

threshold (Battery voltage is rising)

Battery voltage overvoltage hysteresis thresholdVBAT_OV_HYST VBAT decreasing 18 35 89 mV

(Battery voltage is falling), internal threshold

Programmable voltage range for under voltageVBAT_UV VBAT decreasing; VBAT_UV > VBias 2.2 VBAT_OV V

threshold (Battery voltage is falling)

Battery under voltage threshold hysteresis, internalVBAT_UV_HYST VBAT increasing 40 80 125 mV

thershold

Programmable voltage range for threshold voltageVBAT_OK for high to low transition of digital signal indicating VBAT decreasing VBAT_UV VBAT_OV V

battery is OK,

Programmable voltage range for threshold voltageVBAT_OV-

VBAT_OK_HYST for low to high transition of digital signal indicating VBAT increasing 50 mVVBAT_UV

battery is OK,

Overall Accuracy for threshold values, UV, OV,VBAT_ACCURACY Selected resistors are 0.1% tolerance –5% 5%

VBAT_OK

VSTOR-VBAT_OKH VBAT OK (High) threshold voltage Load = 10 µA V

200mV

VBAT_OKL VBAT OK (Low) threshold voltage Load = 10 µA 100 mV

TSD_PROTL The temperature at which the boost converter is OT_Prog = LO 65 °Cdisabled and the switch between VBAT and VSTOR

TSD_PROTH OT_Prog = HI 120is disconnected to protect the battery

Voltage for OT_PROG High setting 2 VOT_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 0.5 V <VIN < 3 V; IIN (DC) = 10 mA –10% 10%

DC input voltage into VIN_DC when charger isVIN_shutoff 40 80 130 mV

turned off

Threshold on VOC_SAMP to disable MPPT VSTOR-15MPPT_Disable V

functionality mV

Voltage node which is used as reference for theVBIAS VIN_DC ≥ 0.5V; VSTOR ≥ 1.8 V 1.21 1.25 1.27 V

programmable voltage thresholds




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bq25504

VSS

VIN_DC

AVSS

VOC_SAMP

VREF_SAMP


LBST VSTOR VBAT VSS

OK_HYST

OK_PROG

VBAT_OK


DEVICE INFORMATION

RGT PACKAGE(TOP VIEW)

Figure 1. bq25504 3mm x 3mm QFN-16 Package

PIN FUNCTIONSPIN

I/O TYPE DESCRIPTIONNO. NAME

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

Switched node for holding the reference set by resistors on VOC_SAMP for MPPT. When MPPT is4 VREF_SAMP Input 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 Output Resistor divider biasing voltage.

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 I/O Connection for storage elements

15 VSTOR Output Connection for the system load, output of the boost converter

16 LBST Input Inductor connection for the boost converter switching node




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16 15 14 13`CHVR

LBST CSTOR

VSTOR

VBAT_OK

bq25504

Solar

Cell

+

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ROC1

ROC2

CREF

ROV2

ROK1

ROK2

ROK3

Battery(>100µF)

VSS

VIN_DC

AVSS

VOC_SAMP

VREF_SAMP


LBST VSTOR VBAT VSS

OK_HYST

OK_PROG

VBAT_OK

4.42 MΩ

1.43MΩ

4.22 MΩ

4.02MΩ

4.42 MΩ

15.62MΩ

0.01µF

4.7µF

22µH

4.7µF

RUV24.42 MΩ

RUV15.60 MΩ

ROV15.90MΩ


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

Figure 2. Typical Solar Application Circuit




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Thermo electric

generator

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16 15 14 13`CHVR

LBST CSTOR

VSTOR

VBAT_OK

bq25504

ROC1

ROC2

CREF

ROV2

ROK1

ROK2

ROK3

Battery(>100µF)

VSS

VIN_DC

AVSS

VOC_SAMP

VREF _SAMP


LBST VSTOR VBAT VSS

OK_HYST

OK_PROG

VBAT_OK

3.32 MΩ

542kΩ

6.12 MΩ

5.62MΩ

10 MΩ

10 MΩ

0.01µF

4.7µF

22µH

4.7µF

RUV26.12MΩ

RUV13.83MΩ

ROV14.42MΩ

VSTOR


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

Figure 3. Typical TEG Application Circuit




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Primary Cell

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LBST CSTOR

VSTOR

VBAT_OK

bq25504VSTOR

ROV2

ROK1

ROK2

ROK3

Battery(>100µF)

VSS

VIN_DC

AVSS

VOC_SAMP

VREF_SAMP


LBST VSTOR VBAT VSS

OK_HYST

OK_PROG

VBAT_OK

3.97 MΩ

976 kΩ

5.05 MΩ

4.48 MΩ

4.7µF

22µH

4.7µF

RUV24.42 MΩ

RUV15.56 MΩ

ROV15.56 MΩ


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

Figure 4. Typical MPPT Disabled Application Circuit




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VSS

VIN_DC

VOC_SAMP

VREF_SAMP

VBATLBST VSTOR VSS

OK_HYST

OK_PROG

AVSS

VBAT_OK

VRDIVOT_PROG VBAT_OV VBAT_UV

Enable

BAT_SAVE

Boost ChargeController

Enable

Vref

Interrupt

Bias Referenceand Oscillator

Battery ThresholdControl

Cold-StartUnit

MPPTController

TemperatureSensingElement

Vref

Vref

UV

OTOK

OV


HIGH-LEVEL FUNCTIONAL BLOCK DIAGRAM

Figure 5. High-level Functional Diagram




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−10

0

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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 3Input Voltage (V)

Effi

cien

cy (

%)

VSTOR = 1.8VVSTOR = 3VVSTOR = 5.5V

IIN = 10µA

G001

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90

100

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 3Input Voltage (V)

Effi

cien

cy (

%)

VSTOR = 3.3 VVSTOR = 1.8 VVSTOR = 5.5 V

IIN = 100µA

G002

20

30

40

50

60

70

80

90

100

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 3Input Voltage (V)

Effi

cien

cy (

%)

VSTOR = 3VVSTOR = 1.8VVSTOR = 5.5V

IIN = 10mA

G003

40

50

60

70

80

90

100

0.01 0.1 1 10 100Input Current (mA)

Effi

cien

cy (

%)


VIN = 2V

G004

40

50

60

70

80

90


Effi

cien

cy (

%)


VIN = 1V

G005

20

30

40

50

60

70

80

90


Effi

cien

cy (

%)


VIN = 0.5V

G006


TYPICAL CHARACTERISTICS

Spacer

Figure 6. Efficiency vs Input Voltage Figure 7. Efficiency vs Input Voltage

Figure 8. Efficiency vs Input Voltage Figure 9. Efficiency vs Input Current

Figure 10. Efficiency vs Input Current Figure 11. Efficiency vs Input Current




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20

30

40

50

60

70

80


Effi

cien

cy (

%)


VIN = 0.2V

G007

0

100

200

300

400

500

600

700

800

900

1000

−60 −40 −20 0 20 40 60 80 100 120Temperature (°C)

VS

TO

R C

urre

nt (

nA)

VSTOR = 1.8VVSTOR = 3VVSTOR = 4V

G008

10

12

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16

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20

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24

−50−40−30−20−10 0 10 20 30 40 50 60 70 80 90 100Temperature (°C)

Tim

e (s

)

G009

150

200

250

300

350

400

−50−40−30−20−10 0 10 20 30 40 50 60 70 80 90 100Temperature (°C)

Tim

e (m

s)

G010

VIN = 1 V, RIN = 20 , VBAT = 100 µF capacitorW VIN = 1 V, RIN = 20 , VBAT = ramping power supplyW


TYPICAL CHARACTERISTICS (continued)

Figure 12. Efficiency vs Input Current Figure 13. VSTOR Quiescent Current vs Temperature

Figure 14. Sample Period vs Temperature Figure 15. Settling Period vs Temperature

Figure 16. Example of Startup with no Battery and Figure 17. Example of VBAT_OK Operation, RampingBattery From 0 V to 3.1 V10 KΩ Load




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VIN = 1 V, RIN = 20 , VBAT = 2.5 V, RBAT = 100 mW W VIN = 1 V, RIN = 20 , VBAT = 3.1 V, RBAT = 100 mW W

VIN = 1 V, RIN = 20 , VBAT = 1.9 V, RBAT = 100 mW W VIN = 1 V, RIN = 20 , VBAT = 3 V, RBAT = 100 mW W


TYPICAL CHARACTERISTICS (continued)

Figure 18. Example of PFM Switching Converter Waveform Figure 19. Example of Output Ripple Voltage DuringOperation at O V Setting

Figure 20. Example of Startup When VBAT is Held Figure 21. Example of Sampling Time for MPPT OperationBelow UV Setting




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DETAILED PRINCIPLE OF OPERATION

OPERATION

The bq25504 is an ultra low quiescent current, efficient synchronous boost converter/charger. The boostconverter is based on a switching regulator architecture which maximizes efficient operation while minimizingstart-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 eitherrechargeable batteries or capacitors can be used as energy storage elements. Figure 5 is a high-level functionalblock 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. Thestart-up below 1.8 V on VSTOR of the boost-converter begins with the Cold-Start sub-system. If the VIN_DC isgreater than VSTOR or VBAT then current may flow until the voltage at the input is reduced or the voltage atVSTOR and VBAT rise. This is considered an abnormal condition and the boost converter/charger does notoperate.

Cold -Start

The cold-start subsystem is used to turn on the device when the voltage present on pin VSTOR is < 1.8 V. Insidethe IC there is a switch (PMOS) between the energy storage capacitor VSTOR and the battery. If a battery isinitially attached to pin VBAT, the PMOS switch is momentary closed and any available charge from the batterycan be dumped onto VSTOR. If the resulting voltage is greater than about 1.8 V, then the bq25504’s biasing andoscillator circuits can be turned on, and start up of the boost converter will be initiated. However, if there isinsufficient energy available in a connected battery, then the PMOS circuit is opened after ~20 ms, and thecold-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 startsubsystem turns on. When the storage capacitor voltage reaches 1.8 V the main boost regulator starts up. Thecold-start circuitry is then turned off after the voltage condition of VSTOR >1.8V and ~32 ms after input powerwas 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 theenergy storage element attached to VBAT to charge up. Figure 22 shows the key threshold voltages. The batterymanagement thresholds are explained later is this section. Cold start is not as efficient as the main boostregulator. If there is not sufficient power available it is possible that the cold start continuously runs and theVSTOR 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 energyavailable from the DC input source. It employs pulse frequency modulation (PFM) mode of control to regulate theinput voltage (VIN_DC) close to the desired reference voltage. The reference voltage is set by the MPPT controlscheme as described in the next section. Input voltage regulation is obtained by transferring charge from theinput to VSTOR only when the input voltage is higher than the voltage on pin VREF_SAMP. The current throughthe inductor is controlled through internal current sense circuitry. The peak current in the inductor is ditheredinternally to set levels to maintain high efficiency of the converter across a wide input current range. Theconverter nominally transfers up to a typical peak of 200 mA of input current. The boost converter is disabledwhen the voltage on VSTOR reaches the OV condition to protect the battery connected at VBAT fromovercharging.

Maximum Power Point Tracking

Maximum power point tracking (MPPT) is implemented in bq25504 in order to maximize the power extractedfrom an energy harvester source. MPPT is performed by periodically sampling a ratio of the open-circuit voltageof the energy harvester and using that as the reference voltage (VREF_SAMP) to the boost converter. Thesampling ratio can be externally programmed using the resistors ROC1 and ROC2. For solar harvesters, theresistive division ratio can be typically set between 0.7-0.8 and for thermoelectric harvesters; a resistive divisionratio of 0.5 is typically used. The exact ratio for MPPT can be optimized to meet the needs of the input sourcebeing used.




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æ öç ÷è ø

OC1

OC1 OC2

RVREF_SAMP = VIN_DC(OpenCircuit)

R + R

under voltage (user programmable) = 2.2 V

under voltage + hyst (internal)

VBAT_OK (user programmable) = 2.4 V

Incre

asin

gV

ST

OR

vo

lta

ge

ground

device absolute max = 5.5 V

charger enable = 1.8 V

Cold start

Main Boost

Charger on

chip enable = 1.4 V

VBAT_OK + hyst (user programmable) = 2.8 V

over voltage – hyst (internal)

over voltage (user programmable) = 3.1 V

Charger off


Internally, the boost converter modulates the effective impedance of the energy transfer circuitry to regulate theinput voltage (VIN_DC) to the sampled reference voltage (VREF_SAMP). A new reference voltage is obtainedevery 16s by periodically disabling the charger for 256ms and sampling a ratio of the open-circuit voltage. Thereference voltage is set by the following expression:

(1)

The internal MPPT circuitry and the periodic sampling of VIN_DC can be disabled by tying the VOC_SAMP pinto VSTOR. When disabled an external reference voltage can be fed to the VREF_SAMP pin. The boostconverter 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 ascapacitors, super capacitors or various battery chemistries. If a capacitor is selected it needs to meet theminimum capacitance of 100 µF. If a battery is used it should be selected to have a minimum capacity equivalentto 100 µF capacitance. To take full advantage of the battery management, the load is normally tied to theVSTOR pin. Also, if there is large load transients or the storage element has impedance then it is necessary toadd 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 IChas internal circuitry to manage the voltage across the storage element and to optimize the charging of thestorage element. For successfully extracting energy from the source, three different threshold voltages must beprogrammed 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 ofthe IC. Figure 22 shows a plot of the voltage at the VSTOR pin and the various threshold voltages. For the bestoperation of the system, the VBAT_OK should be used to determine when a load can be applied or removed. Adetailed description of the three voltage thresholds and the procedure for designing the external resistors forsetting the three voltage thresholds are described next.

Figure 22. Figure Shows the Relative Position of Various Threshold Voltages(Threshold Voltages are From Typical Solar Application Circuit in Figure 2)




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1æ öç ÷è ø

UV2

UV1

RVBAT_UV = VBIAS +

R

31

2

æ öç ÷è ø

OV2

OV1

RVBAT_OV = VBIAS +

R

1æ öç ÷è ø

OK2

OK1

RVBAT_OK_PROG = VBIAS +

R

1æ öç ÷è ø

OK2 OK3

OK1

R + RVBAT_OK_HYST = VBIAS +

R


Battery Undervoltage Protection

To prevent rechargeable batteries from being deeply discharged and damaged, and to prevent completelydepleting charge from a capacitive storage element, the undervoltage (VBAT_UV) threshold must be set usingexternal resistors. The VBAT_UV threshold voltage when the battery voltage is decreasing is given byEquation 2:

(2)

The sum of the resistors must be 10 MΩ i.e., RUV1 + RUV2 = 10 MΩ. The undervoltage threshold when batteryvoltage is increasing is given by UV_HYST. It is internal set to the under voltage threshold plus an internalhysteresis voltage denoted by VBAT_UV_HYST. For proper functioning of the IC and the overall system, theload must be connected to the VSTOR pin while the storage element must be connected to the VBAT pin. Oncethe 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_UVthreshold should be considered a fail safe to the system and the system load should be removed or reducedbased on the VBAT_OK signal.

Battery Overvoltage Protection

To prevent rechargeable batteries from being exposed to excessive charging voltages and to prevent overcharging a capacitive storage element, the over-voltage (VBAT_OV) threshold level must be set using externalresistors. This is also the voltage value to which the charger will regulate the VSTOR/VBAT pin when the inputhas sufficient power. The VBAT_OV threshold when the battery voltage is rising is given by Equation 3:

(3)

The sum of the resistors must be 10 MΩ i.e. ROV1 + ROV2 = 10 MΩ. The overvoltage threshold when batteryvoltage is decreasing is given by OV_HYST. It is internal set to the over voltage threshold minus an internalhysteresis 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 theVBAT_OV_HYST level. When there is excessive input energy, the VBAT pin voltage will ripple between theVBAT_OV and the VBAT_OV_HYST levels.

CAUTION

It should also be noted that if VIN_DC is higher than VSTOR and VSTOR is higherthan VBAT_OV, the input VIN_DC is shorted to ground to stop further charging of theattached battery or capacitor. It is critical that if this case is expected, the sourceimpedance on VIN_DC is made higher than 20 Ω, it must not be a low impedancesource.

Battery Voltage in Operating Range (VBAT_OK Output)

The IC allows the user to set a programmable voltage independent of the overvoltage and undervoltage settingsto indicate whether the battery voltage is at an acceptable level. When the battery voltage is decreasing thethreshold is by Equation 4

(4)

When the battery voltage is increasing, the threshold is by Equation 5

(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 isequal to the VSTOR voltage and the logic low level is ground. The logic high level has ~20 KΩ internally in seriesto limit the available current to prevent MCU damage until it is fully powered. The VBAT_OK_PROG thresholdmust be greater than or equal to the UV threshold. For the best operation of the system, the VBAT_OK shouldbe 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. Theapplication should provide this battery protection and ensure that the ambient temperature is never elevatedgreater than the expected operational range of 85°C.

The bq25504 uses an integrated temperature sensor to monitor the junction temperature of the device. If theOT_PROG pin is tied low then the temperature threshold for thermal protection is set to TSD_ProtL which is65°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. Oncethe temperature of the device drops below this threshold, the boost converter/charger can resume operation. Inorder to avoid unstable operation near the overtemp threshold, a built-in hysteresis of approximately 5°C hasbeen implemented. Care should be taken to not over discharge the battery in this condition since the boostconverter/charger is disabled. However, if the supply voltage drops to the VBAT_UV setting, then the switchbetween 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 currentcapability 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 followsthe voltage stored on the CREF capacitor. This capacitor is very sensitive to leakage since the holding period isaround 16 seconds. As the capacitor voltage drops due to any leakage, the input regulation voltage will also dropand this can prevent proper operation from extraction the maximum power from the input source. Therefore, it isrecommended 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. Acapacitor 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) andground (VSS, Pin 1). For energy harvesters which have a source impedance which is dominated by a capacitivebehavior, the value of the harvester capacitor should scaled according to the value of the output capacitance ofthe energy source , but an initial value of 4.7 µF is recommended.




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Storage capacitor:An additional storage capacitor CBAT, either stand-alone, or in parallel with the battery should be attachedbetween Pin 14 (VBAT) and GND. The value of this capacitor should be selected to meet the needs of any loadattached to the battery. For instance, some Li-ion batteries or thin-film batteries may not have the currentcapacity to meet the surge current requirements of an attached low power radio. Therefore, adding a capacitormay 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 toCSTOR 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 currentsand high switching frequencies. If the layout is not carefully done, the boost converter/charger could showstability problems as well as EMI problems. Therefore, use wide and short traces for the main current path andfor the power ground paths. The input and output capacitor, as well as the inductor should be placed as close aspossible to the IC.

The resistors that program the thresholds should be placed as close as possible to the input pins of the IC tominimize 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 controlground 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 requiresspecial attention to power dissipation. Many system-dependent issues such as thermal coupling, airflow, addedheat sinks and convection surfaces, and the presence of other heat-generating components affect thepower-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 CharacteristicsApplication Note (SZZA017) and the IC Package Thermal Metrics Application Note (SPRA953).




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PACKAGE OPTION ADDENDUM

www.ti.com 17-Oct-2011

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status (1) Package Type PackageDrawing

Pins Package Qty Eco Plan (2) Lead/Ball Finish

MSL Peak Temp (3) Samples

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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

(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 availabilityinformation 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 thatlead 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 betweenthe 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 weightin 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 informationprovided 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 andcontinues 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.

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TAPE AND REEL INFORMATION

*All dimensions are nominal

Device PackageType

PackageDrawing

Pins SPQ ReelDiameter

(mm)

ReelWidth

W1 (mm)

A0(mm)

B0(mm)

K0(mm)

P1(mm)

W(mm)

Pin1Quadrant

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

PACKAGE MATERIALS INFORMATION


Pack Materials-Page 1

*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

PACKAGE MATERIALS INFORMATION


Pack Materials-Page 2

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Ultra Low Power Boost Converter with Battery Management ... · All the capabilities of bq25504 are packed into a small foot-print16-lead3 mm x 3 mm QFN package. ORDERING INFORMATION