A 330nA Charger and Battery g yManagement IC for Solar and

Thermoelectric Energy HarvestingThermoelectric Energy Harvesting

Yogesh RamadassTexas Instruments

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Self-Powered Applications

Electronic Shelf LabelsSolar KeyboardO SConvenience

Environmental Awareness

Occupancy Sensor

Pipelines Oil RigSmoke Detector

2

Hard to Reach Smoke Detector

Energy Harvesting SystemBattery, Super

capacitor

Battery Power good

Solar

ChI t f

Battery Management

Power good indicatorMPPT

Energy R l t Radio ChargerInterface

Power

gyHarvester Regulator Micro Proc.

Thermol t i Cold Start

Power Management IC

electric

3Charger, Regulator and Battery Management

Outline

• Design Goalsg

• Chip Architecture and Circuit DetailsChip Architecture and Circuit Details

• Experimental Results• Experimental Results

S• Summary

4

Design Goals

LBST CSTOR VBAT

Battery

SolarCell

+

-

ROC2

CREF

ROK1

R

VBAT_OK

BQ25504Energy Input 80mV to 3V ROC1

CREF ROK2

ROK3

to 3V330mV cold start

300mW max power

ROV1

ROV2

RUV1

RUV2

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Design Goals

LBST CSTOR VBAT

Battery

SolarCell

+

-

ROC2

CREF

ROK1

R

VBAT_OK

Energy Input 80mV to 3V

BQ25504

ROC1CREF ROK2

ROK3

to 3V330mV cold start

300mW max power

ROV1

ROV2

RUV1

RUV2Open circuit voltage based maximum power

point tracking

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0% to 100%

Design Goals

LBST CSTOR VBAT

Battery

SolarCell

+

-

ROC2

CREF

ROK1

R

VBAT_OK

Energy Input 80mV to 3V

BQ25504

ROC1CREF ROK2

ROK3

to 3V330mV cold start

300mW max power

ROV1

ROV2

RUV1

RUV2Open circuit voltage based maximum power

point tracking Under voltage and

Over voltage

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0% to 100% 2.2V to 5.25V+/- 3% Accuracy

Design Goals

LBST CSTOR VBAT

Battery

SolarCell

+

-

ROC2

CREF

ROK1

R

VBAT_OK

Energy Input 80mV to 3V

BQ25504

ROC1CREF ROK2

ROK3 Battery OK2.3V to 5.25V

to 3V330mV cold start

300mW max power

ROV1

ROV2

RUV1

RUV2Open circuit voltage based maximum power

point tracking Under voltage and

Over voltage

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0% to 100% 2.2V to 5.25V+/- 3% Accuracy

Design Goals

LBST CSTOR VBAT

Battery / Super cap2.2V to 5.25V

SolarCell

+

-

ROC2

CREF

ROK1

R

VBAT_OK

Energy Input 80mV to 3V

BQ25504

ROC1CREF ROK2

ROK3 Battery OK2.3V to 5.25V

to 3V330mV cold start

300mW max power

ROV1

ROV2

RUV1

RUV2Open circuit voltage based maximum power

point tracking Under voltage and

Over voltage

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0% to 100% 2.2V to 5.25V+/- 3% Accuracy

Overall Chip ArchitectureCharger and• Charger andMPPT

• Cold Start• Cold Start• Battery

managementmanagement• Battery isolation

switchswitch• House keeping

– ResetReset– Oscillator– Bias

10

Charger Architecture

I t

SynchronousPower Stage

C t ll

Reference& MPPT

ENZ

+

-

Input

R1 Vsamp

Controller+-

ENZENCREFR2

This work

• Synchronous boost converter with input regulationregulation

• Hysteretic controller with 55nA quiescent current• Fractional open circuit voltage based MPPT

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Fractional open circuit voltage based MPPT• Zero power from battery for MPPT

Controller ArchitecturePower Stage withCurrent Sensors

• Main comparator detects if VIN_DC > VREF to enable charger

• COMP2 detects OV condition to turn off charger

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• COMP2 detects OV condition to turn off charger• Safety timers to detect saturation

Controller Architecture

Main Comparator

• Main comparator detects if VIN_DC > VREF to enable charger

• COMP2 detects OV condition to turn off charger

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• COMP2 detects OV condition to turn off charger• Safety timers to detect saturation

Charger Operation

LBST

CS2

VIN_DC InductorCurrent

ISET CS1 : I = I

VSTOR

LBST ISET CS1 : IL = ISETLS_OFF, HS_ON

HS_ONCSTORCS1LS_ON

TimeLS_ON

CS2 : IL = 0

• When VIN_DC > VREF, OV = lo, CHG_EN = hi– LS_ON = hi and LS_ON remains high till IL hits ISET.

• Once CS1 goes high (i.e IL=ISET), – LS_ON =lo and HS_ON = hi

HS ON i hi h ill I 0 (CS2 d hi )

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• HS_ON remains high till IL = 0 (CS2 detects this)

Current SensorVIN IND

IIIND

IIND

WL

WL

NIND

N

POWER FET SENSE FET

• Feedback controlled current sensor

POWER FET SENSE FET

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• Sensed current is 4000 (=N) times smaller than inductor current

Controller Architecture

O lOutput voltage determined

by OV setpoint

• Main comparator detects if VIN_DC > VREF to enable charger

• COMP2 detects OV condition to turn off charger

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• COMP2 detects OV condition to turn off charger• Safety timers to detect saturation

Maximum Power Point Tracking256ms

16sEN

S l TEGSolar TEGMPPT

fraction ~80% 50%

• Open circuit voltage based MPPTOpen circuit voltage based MPPT• Charger periodically turned off using EN signal• IC samples and holds fraction of OCV on external

it

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capacitor• Charger regulates input to value held on capacitor

Batt. Management Architecture ENVSTOR EN

OVS

VSTOR

UZ

ENZ

Rh

UZ

R+

-1.25VR1

R2

UVC1

EN

• Independent, resistor programmable UV, OK, OVUnder Voltage

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• State machine with low power 2kHz oscillator• Duty cycled and sampled reference

VSTORBatt. Management Architecture

ENVSTOR

UZ

ENZ

EN

OVS

R3

Rh

UZ

RKZ

R4

R3+

-1.25VR1

R2

UVC1

R5 +

- OK1.25V C2EN

EN

• Independent, resistor programmable UV, OK, OVUnder Voltage Battery OK

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• State machine with low power 2kHz oscillator• Duty cycled and sampled reference

VSTORBatt. Management Architecture

ENVSTOR

UZ

ENZ

OVS

EN

OVS

R3 R6

Rh

UZ

RKZ

OVSZ

OVS

R4

R3

+

-R7

R6+

-1.25VR1

R2

UV 1.25VC1C3

OVSZ

OVS OVS

OV_REF

R5 +

- OK1.25V C2

OVS OVSEN

ENOver voltage

• Independent, resistor programmable UV, OK, OVUnder Voltage Battery OK

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• State machine with low power 2kHz oscillator• Duty cycled and sampled reference

Battery Isolation

VIN_DC

LBST

VSTOR VBAT

CSTOR

Cold Start

ChargerMPPT

Battery ManagementComparators

State MachineVBA

OV UV

OK

• VSTOR node connected to battery only after UV

OscPORp

BiasVRDIV

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• Prevents battery damage

Main Oscillator

• Relaxation oscillator frequency ~ 2kHz

Regulator

• Relaxation oscillator frequency ~ 2kHz• Sub-regulation reduces quiescent current• Iq 50nA @ 27C and 100nA across temperature

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Iq 50nA @ 27C and 100nA across temperature

Main Oscillator

• Relaxation oscillator frequency ~ 2kHz

ReferenceRegulator

• Relaxation oscillator frequency ~ 2kHz• Sub-regulation reduces quiescent current• Iq 50nA @ 27C and 100nA across temperature

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Iq 50nA @ 27C and 100nA across temperature

Main Oscillator

• Relaxation oscillator frequency ~ 2kHz

CoreReferenceRegulator

• Relaxation oscillator frequency ~ 2kHz• Sub-regulation reduces quiescent current• Iq 50nA @ 27C and 100nA across temperature

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Iq 50nA @ 27C and 100nA across temperature

Main Oscillator

• Relaxation oscillator frequency ~ 2kHz

ComparatorCoreReferenceRegulator

• Relaxation oscillator frequency ~ 2kHz• Sub-regulation reduces quiescent current• Iq 50nA @ 27C and 100nA across temperature

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Iq 50nA @ 27C and 100nA across temperature

Main Oscillator

• Relaxation oscillator frequency ~ 2kHz

Level ShifterComparatorCoreReferenceRegulator

• Relaxation oscillator frequency ~ 2kHz• Sub-regulation reduces quiescent current• Iq 50nA @ 27C and 100nA across temperature

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Iq 50nA @ 27C and 100nA across temperature

• Function : Start system with depleted batteryCold Start

• Function : Start system with depleted battery• Architecture : Input powered boost converter• Startup voltage / power = 330mV / 5uW p g p

Enable

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Switch

Cold Start CircuitBST

B

• Low Vt low side switch

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• Body diode of main charger high side switch

Cold Start CircuitBST

B

Power on reset

• Body diode of main charger high side switch

330mV threshold

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• Low Vt low side switch

Cold Start CircuitBST

B

Power on reset 300kHz ring

• Body diode of main charger high side switch

330mV thresholdg

oscillator

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• Low Vt low side switch

Cold Start CircuitBST

B

Power on reset 300kHz ring 4X charge pump

• Body diode of main charger high side switch

330mV thresholdg

oscillator gate drive

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• Low Vt low side switch

Outline

• Design Goalsg

• Chip Architecture and Circuit DetailsChip Architecture and Circuit Details

• Experimental Results• Experimental Results

S• Summary

32

Normal System Startup

VBAT OK

Battery OKgoes high

VBAT_OK

Switch between VSTOR and VBAT

Battery atOV = 3.3V

VSTOR

VBAT

closes at UV

VBAT

VIN = 330mVOpen circuit voltage samplingfor MPPT

Cold Start Charger On OVCold Start Charger On OV

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Maximum Power Point TrackingInput Open Circuit Voltage (OCV) 2V

1V1V Charger regulates VIN t 80%Periodic

1.6VVIN to 80% of OCV

Periodic sampling of OCV

Input Voltage 16s 16s

0.8V 0.8V

p g(VIN) 16s 16s

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Charger Efficiency• Single cell solar operation in indoor light (200 lux)• Single cell solar operation in indoor light (200 lux)• Harvesting from thermo electric generators

Eff Vs Iin Eff Vs Vin

• 35% efficiency with 10uA input at 0.5V

• 38% efficiency with 100mV input at 10mA

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input at 0.5V

• > 80% above 100uA.

input at 10mA

• >80% above 0.5V

Battery Management• Quiescent current : 180 nA• Trip point accuracy < +/-2% (untrimmed)Trip point accuracy / 2% (untrimmed)

30 devices measured at -40 27 and 85Cat 40, 27 and 85C

Mean : 1.24VSi 4 3 VSigma : 4.3mV

• OV and UV range : 2V to 5.5V

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SummaryTechnology : 0 35um• Technology : 0.35um

• Iq = 330nA • ChargerCharger

– > 80% eff @ 0.5V– Zero power MPPT

H t f 80 V– Harvest from 80mVand 5uW of power

• Cold Start– 330mV and 5uW

of power• Battery ManagementBattery Management

– Independently programmable UV, OK, OV, OT– Li-ion, NiMH, Supercaps

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Complete battery and power management solution for energy harvesting

Acknowledgements

• Colleagues at TI

– Karthik KadirvelMike Corry– Mike Corry

– Umar Lyles– John CarpenterJohn Carpenter– Brian Lum-Shue Chan– Tony Antonacci– Vadim Ivanov

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