Highly Efficient, Dual Regulated Output, Ambient AEM10940 … · 2017-12-13 · - For any type of rechargeable battery or (super)capacitor - Fast supercapacitor charging Smallest

AEM10940

Highly Efficient, Dual Regulated Output, Ambient

Energy Manager for up to 2 cells solar panels

Document DS_AEM10940_REV1.4 Data Sheet Page 1 of 16 Copyright © 2016 e-peas SA

FEATURES

Ultra-low-power start-up

- Cold start from 380 mV input voltage and 11 µW input

power (typical)

Ultra-low-power Boost regulator

- Open circuit voltage sensing for MPPT every 16 s

- Configurable MPPT with single-pin programming

Selectable Voc ratios of 80 and 90% - Input voltage operation range from 100 mV to 2.5 V

- MPPT voltage operation range from 100 mV to 1.3 V

Integrated LDO regulator at low voltage

- 1.8 V, high efficiency

- Up to 10 mA load current

Integrated LDO regulator at high voltage

- Configurable from 2.2 V to 4.2 V

- Up to 80 mA load current with 300 mV drop-out

- Power gated by external control

Flexible energy storage management

- Programmable overcharge and overdischarge protection

- For any type of rechargeable battery or (super)capacitor

- Fast supercapacitor charging

Smallest footprint, smallest BOM

- Only seven passive external components

APPLICATIONS

• Harvesting from photovoltaic cell (PV)

• Industrial monitoring

• Indoor geolocation

• Home automation

• Wearables

• E-health monitoring

• Wireless Sensor Nodes

DESCRIPTION

The AEM10940 is an integrated energy management subsystem that extracts DC power from PV cells or TEGs to simultaneously store energy in a rechargeable element and supply the system with two independent regulated voltages. This allows product designers and engineers to extend battery lifetime and ultimately get rid of the primary energy storage element in a large range of wireless applications like industrial monitoring, geolocation, home automation, wearables...

The AEM10940 harvests the available input current up to 25 mA. It integrates an ultra-low-power Boost converter to charge a storage element, such as a Li-Ion battery, a thin film battery or a super- or conventional capacitor. The Boost converter operates with input voltages in a range of 100 mV to 2.5 V. With its unique cold-start circuit, it can start operating with empty storage elements at an input voltage as low as 380 mV and an input power of just 11 µW.

The low voltage supply typically drives a microcontroller at 1.8 V. The high voltage supply typically drives a radio transceiver at a configurable voltage. Both are driven by highly efficient LDO (Low Drop-Out) regulators for low noise and high stability.

Configuration pins determine various operating modes by setting predefined conditions for the energy storage element (overcharge or overdischarge), and by selecting the voltage of the high voltage supply. However, special modes can be obtained at the expense of a few configuration resistors.

The chip integrates all the active elements for powering a typical wireless sensor. With only seven external components, integration is maximum, footprint and BOM are minimum, optimizing the time-to-market and costs of WSN designs in all markets.

Five identical capacitors and two inductors are required, available respectively in the small 0402 and 0603 SMD formats.

DEVICE INFORMATION PART NUMBER PACKAGE BODY SIZE

AEM10940_10A QFN 24-pin 5mm x 5mm

TYPICAL APPLICATION CIRCUIT

Figure 1 – Application Circuit

PV Cell Li-Ion Battery

AEM10940-QFN24

CHV

CLVSWBUCK

BUCK

HVOUT

LVOUT

GND

HVRDY

LVRDY

LOBATT

SELMPP CFG2 CFG1 CFG0

RadioTransceiver

VDD Vss

Micro-controller

VDD Vss

ENHV

BUFSRC

SWBOOST

LBOOST

CSRC

BOOST

CBOOST

LBUCK

CBUCK

SET_OVCH SET_CHRDY SET_OVDIS FB_HV

SRC BATT

STONBATT

NC

Data Sheet AEM10940

Document DS_AEM10940_REV1.4 Page 2 of 16 Copyright © 2016 e-peas SA

TABLE OF CONTENTS Features ......................................................................................... 1

Applications ................................................................................. 1

Description ................................................................................... 1

Device information ................................................................... 1

Typical Application Circuit ................................................... 1

Table of Contents....................................................................... 2

Figures .......................................................................................... 2 Tables ............................................................................................ 2

Absolute Maximum Ratings .................................................. 3

Thermal Resistance .................................................................. 3

Recommended Operating Conditions .............................. 3

Electrical Characteristics ....................................................... 4

Pin Configuration and Description .................................... 5

Functional Block Diagram ..................................................... 6

Theory of Operation ................................................................. 6

Power Path ................................................................................. 7 Operating regions ................................................................... 7 Configuration ............................................................................ 8 Charge Management State Machine ............................... 8 Startup Mechanism ................................................................ 8 Overvoltage Protection ........................................................ 9 Shutdown Mechanism ........................................................... 9 MPP and Boost Converter Regulation ........................... 9 Buck Converter Regulation ................................................ 9 Low Voltage Output ............................................................... 9 High Voltage Output ............................................................... 9

Application Information ...................................................... 10

Built-in Configurations .......................................................10 Custom Configuration .........................................................10 Power Gating ...........................................................................11 Energy Source Information ..............................................11 Storage Element Information ..........................................11 External Inductors Information .....................................11 External Capacitors Information ...................................11

Typical Application Circuits .............................................. 12

Example Circuit 1 ..................................................................12 Example Circuit 2 ..................................................................12

Performance Data .................................................................. 13

Startup Timing Diagram ....................................................13 Shutdown Timing Diagram ..............................................13 Boost Conversion Efficiency ............................................14 Low Voltage Conversion Efficiency (Includes LDO

and Buck Converter) ............................................................14 Low Voltage LDO Load Regulation ...............................14 High Voltage LDO Load Regulation ..............................14

Package Information ............................................................. 15

FIGURES

Figure 1 - Pinout Diagram ............................................................5

Figure 2 - Functional Block Diagram ......................................6

Figure 3 - Power Path.....................................................................7

Figure 4 - Operating Regions ......................................................7

Figure 5 - Charge Management State Diagram ...................8

Figure 6 - Custom Configuration Resistors ....................... 10

Figure 7 - Power Gating Scheme ............................................ 11

Figure 8 - Example Application 1 .......................................... 12

Figure 9 - Example Application 2 .......................................... 12

Figure 10 - Startup Timing ....................................................... 13

Figure 11 - Shutdown Timing .................................................. 13

Figure 12 - Boost Efficiency at 2.8 V..................................... 14



Figure 15 - LV efficiency versus battery voltage ............ 14

Figure 16 - LV Efficiency versus output current ............. 14

Figure 17 - LV LDO Load Regulation .................................... 14

Figure 18 - HV LDO Load Regulation ................................... 14

TABLES

Table 1 - Absolute Maximum ratings ......................................3

Table 2 - Thermal Data ..................................................................3

Table 3 - Recommended Operating Conditions .................3

Table 4 - Electrical Characteristics ..........................................4

Table 5 - Pins description .............................................................5

Table 6 - Usage of CFG2 .................................................................8

Table 7 - Usage of SELMPP ..........................................................9

Table 8 - Usage of CFG2, CFG1, CFG0 ................................... 10

Table 9 - Customization: Resistors to Voltages ............... 10

Table 10 - Customization: Voltages to Resistors ............ 10

Table 11 – Static Power Schemes .......................................... 11

Table 12 - Threshold Voltages, Example 1 ........................ 12

Table 13 - Threshold Voltages, Example 2 ........................ 12

Data Sheet AEM10940


ABSOLUTE MAXIMUM RATINGS

Parameter Rating

Vsrc 2.75 V

Operating junction temperature -40°C to +125°C

Storage temperature -65°C to +150°C

Table 1 - Absolute Maximum ratings

THERMAL RESISTANCE

Package 𝚯𝐉𝐀 𝚯𝐉𝐂 Unit

QFN24 tbd tbd °C/W

Table 2 - Thermal Data

ESD CAUTION

ESD (ELECTROSTATIC DISCHARGE) SENSITIVE DEVICE

These devices have limited built-in ESD protection and damage may thus occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality.

RECOMMENDED OPERATING CONDITIONS

Symbol Parameter Min Typ Max Unit

External Components

CSRC Capacitance of the source buffering external capacitor 8 10 µF

CBOOST Capacitance of the Boost converter external capacitor 8 10 µF

LBOOST Inductance of the Boost converter external inductor 4 10 25 µH

CBUCK Capacitance of the Buck converter external capacitor 8 10 µF

LBUCK Inductance of the Buck converter external inductor 4 10 25 µH

CLV Capacitance of the external capacitor decoupling the low voltage LDO regulator

8 10 14 µF

CLH Capacitance of the external capacitor decoupling the high voltage LDO regulator

8 10 14 µF

RT Equal to R1 + R2 + R3 + R4 (see fig. 3)

Resistance of the optional resistor ladder setting the charge management thresholds voltage in custom configuration

1 10 100 MΩ

RV Equal to R5 + R6 (see fig. 3)

Resistance of the optional resistor divider setting the HV output voltage in custom configuration

1 10 40 MΩ

Logic input pins

VenhvIH Logic input levels on the ENHV control input1

Logic High Vlv-0.25 Vlv 2.5 V

VenhvIL Logic Low -0.25 0 0.25

VcfgH Logic input levels on configuration inputs

SELMPP, CFG0, CFG1, CFG2

Logic High Connect to BUCK

VcfgL Logic Low Connect to GND

Table 3 - Recommended Operating Conditions

Note 1: ENHV can be dynamically driven by a logic signal issued from the LV domain. Full rail-to-rail logic swing is recommended to avoid increasing the quiescent current. For a static usage, connect to BUCK (High) or GND (Low).

Data Sheet AEM10940


ELECTRICAL CHARACTERISTICS

Symbol Parameter Conditions Min Typ Max Unit

Power conversion

Vsrc Voltage across the energy source

During coldstart 380 2500 mV

Vsrc After coldstart 100 2500

PsrcCS Source power required for cold start

During coldstart 11 µW

Vboost Voltage on the BOOST node During normal operation

2.5 4.75 V

Vbuck Voltage on the BUCK node 2 2.2 2.5

Storage element

VbattBAT Voltage on the storage element

Rechargeable battery 2.5 4.5 V

VbattCAP Capacitor 0 4.5 V

Tcrit Time before shutdown after

LOBATT asserted 400 600 800 ms

Low-voltage LDO regulator

Vlv Voltage on the LVOUT output 1.8V V

Ilv Load current from the LVOUT

output 300mV dropout 0 10 mA

High-voltage LDO regulator

Vhv Voltage on the HVOUT output Ilv = 30mA 2.2V Vbatt-0.3 V

Ihv Load current from the HVOUT

output 300mV dropout 0 80 mA

Logic output pins

VOH Logic output levels on the status

outputs LOBATT, LVRDY, HVRDY

Logic High 1.7 V

VOL Logic Low 0.1

Table 4 - Electrical Characteristics

Data Sheet AEM10940


PIN CONFIGURATION AND DESCRIPTION AEM10940-QFN24

Package QFN24 5 x 5 mm

Figure 1 - Pinout Diagram

Exposed pad should be connected to Ground

NAME PIN

NUMBER FUNCTION

Power pins

SRC 5 Connection to the harvested energy source (PV cell)

BUFSRC 4 Connection to a capacitor buffering the energy source, input of the Boost converter

SWBOOST 6 Switching node of the Boost converter

BOOST 8 Output of the Boost converter, input of the Buck converter, input of the high voltage

LDO regulator, internally connectable to BATT

BATT 20 Connection to the energy storage element, battery or capacitor

Cannot be left floating, see application information page 11

SWBUCK 9 Switching node of the Buck converter

BUCK 10 Output of the Buck converter, input of the low voltage LDO regulator

HVOUT 21 Output of the high voltage LDO regulator, typically powering the radio subsystem

LVOUT 15 Output of the low voltage LDO regulator, typically powering the microcontroller

Configuration pins

STONBATT 14 Pin reserved for future use. Connect to ground.

SELMPP 7 Selection of the MPP ratio, see specification page 9

Cannot be left floating CFG2 11

Selection of the built-in threshold voltages, see specification page 10

CFG1 12

CFG0 13

SET_OVCH 1 Node to customize the OverCharge voltage threshold

See application

information page 10

SET_CHRDY 2 Node to customize the ChargeReady voltage threshold

SET_OVDIS 3 Node to customize the OverDischarge voltage threshold

FB_HV 23 Feedback node to customize the high voltage LDO regulator

Control pins

ENHV 16 Active high logic input to enable operation of the high voltage LDO regulator

See application information page 11

Status pins

LOBATT 19 Logic output signaling imminence of shutdown because of insufficient energy

HVRDY 18 Logic output signaling the validity of the high voltage LDO regulator

LVRDY 17 Logic output signaling the validity of the low voltage LDO regulator

Other pins

GND 24

Ground connection, should be solidly tied to the PCB ground plane Exposed Pad

NC 22 Not connected, leave open or tie to ground

Table 5 - Pins description

NC

HV

OU

T

BA

TT

LO

BA

TT

GN

D

FB

_H

VB

OO

ST

SW

BU

CK

BU

CK

SE

LM

PP

CF

G2

CF

G1

BUFSRC

SRC

SWBOOST

SET_OVCH

SET_CHRDY

SET_OVDIS

HVRDY

LVRDY

ENHV

LVOUT

CFG0

STONBATTTop View

AEM10940

6

1

2

3

4

5

18

17

16

15

14

13

24 23 22 21 20 19

7 8 9 10 11 12

Data Sheet AEM10940


FUNCTIONAL BLOCK DIAGRAM

Figure 2 - Functional Block Diagram

THEORY OF OPERATION

The AEM10940 is a full-featured energy efficient power management subsystem able to charge a storage element (battery or supercapacitor, connected to BATT) from an energy source (connected to SRC), typically a miniaturized energy harvester (PV cell). The device manages the transfer of energy from the source and the storage element towards two power supply outputs (LVOUT and HVOUT) at different operating voltages.

Through four configuration pins (CFG2, CFG1, CFG0 and SELMPP), the user assigns a particular operating mode among a selection that covers most application

requirements, without any dedicated external component. Special modes are achieved with the optional high-valued resistors R1 to R6 (connected to SET_OVCH, SET_CHRDY, SET_OVDIS and FB_HV).

A logic control pin is provided (ENHV) to activate or deactivate the LDO regulator that feeds the high voltage system load.

The status of these regulators is reported through dedicated status pins (HVRDY and LVRDY). An additional status (LOBATT) reports when the subsystem is about to shut down due to energy shortage.

High VoltageLDO Control

Power Management Controller

Optional

State Control

Optional

Low VoltageLDO Control

SRC

GND

LVOUT

SET_CHRDY

LOBATT

EnergySource

MPPControl

SELMPP

EnergyStorage

BATT

StorageControl

BUFSRC SWBOOST

BoostControl

BOOST

SWBUCK

BUCK

LBUCK

CBUCK

Vbuck

BuckControl

Vbuck

CLV

HVOUT

CHV

FB_HV

R6

R5

CSRC CBOOST

R2

R3

R4

R1

Cold Start

1 V Ref

LBOOST

1 V Ref

Voltage Reference

Vboost

Vboost

HVRDY LVRDY

CFG2

CFG1

CFG0

ENHV

Microcontroller

HV Load

LV Load

1 V Ref

SET_OVDIS

SET_OVCH

STONBATT

Data Sheet AEM10940


POWER PATH

Figure 3 - Power Path

The above diagram depicts a simplified view of the internal power path of the AEM10940.

The energy source is connected to SRC and delivers power to the subsystem at optimal levels of voltage (Vsrc) and current (Isrc), the so-called MPP (Maximum Power Point). Periodically, the MPP control circuit disconnects the source from the pin BUFSRC with the transistor Q1, in order to measure the open-circuit voltage of the harvester. BUFSRC is decoupled by the capacitor CSRC, which smooths the voltage against the current pulses induced by the Boost converter.

The heart of the power path is a cascade of two regulated switching converters, namely the Boost converter and the Buck converter.

The Boost (or step-up) converter elevates the voltage available at BUFSRC to a level suitable to charge the storage element, in the range 2.2 V to 4.75 V, according to the selected operating mode. This voltage (Vboost) is available at the pin BOOST. The switching transistors of the Boost converter are Q3 and Q4, with the switching node available externally at SWBOOST. The reactive power components are the external inductor and capacitor LBOOST and CBOOST.

The storage element is connected to the pin BATT, at a voltage Vbatt. This node is linked to BOOST through the transistor Q2. In normal operation, this transistor effectively shorts the battery to the BOOST node (Vbatt = Vboost). When energy harvesting is occurring, the Boost converter delivers a current that is shared between the battery and the loads. Q2 is switched off to disconnect the battery when there is a risk of overdischarge.

The Buck (or step-down) converter lowers the voltage from Vboost to a constant value Vbuck of 2.2 V. This voltage is available at the pin BUCK. The switching transistors of the Buck converter are Q5 and Q6, with the switching node available externally at SWBUCK. The reactive power components are the external inductor and capacitor LBUCK and CBUCK.

Vboost feeds the high voltage LDO regulator that powers its load through the pin HVOUT. This regulator delivers a clean voltage (Vhv) adjustable between 2.2 V and Vbatt-0.3 V with a maximum current of 80 mA. The series pass transistor of the regulator is Q7, and the output is decoupled by the external capacitor CHV.

Vbuck feeds the low voltage LDO regulator that powers its load through the pin LVOUT. This regulator delivers a clean fixed voltage (Vlv) of 1.8 V at a maximum current of 10 mA. The series pass transistor of the regulator is Q8, and the output is decoupled by the external capacitor CLV.

The Boost and Buck converters as well as the LDO regulators demonstrate excellent power conversion ratios, as shown in the performance data section (page 14).

The operation of the AEM10940 is best understood by examining the behavior over the voltage span of the BOOST node, which is depicted below.

OPERATING REGIONS

Figure 4 - Operating Regions

The Cold Start region corresponds to a state where all nodes are deeply discharged. As soon as a sparse amount of energy becomes available at the source pin, the cold start mechanism, which involves a charge pump, raises Vboost up to a voltage of 2 V.

High VoltageLDO Regulator

Low VoltageLDO Regulator

BuckConverter

BoostConverter

Vsrc

Vbatt

EnergySource

EnergyStorage

CBOOST

HVLoad

LVLoad

Vhv

VlvLBOOST LBUCK

CSRCCBUCK CLV

CHV

BATT

SRC

BOOST

SWBOOST SWBUCK BUCK

HVOUT

LVOUTBUFSRCQ1

Q2

Q3 Q6

Q4 Q5

Q7

Q8

Vtop+

Vtop-

Vboost

0 V

1 V

2 V

3 V

4 V

Vovdis

Vchrdy

Boost-Buck Region

Top Voltage Region

No Buck Region

Cold StartRegion

VovchOverCharge

threshold

ChargeReadythreshold

OverDischargethreshold

Data Sheet AEM10940


At that stage, the Boost regulator is switched on and continues the process of charging the BOOST node with the energy delivered by the source. However, the Buck regulator is not yet activated, but its transistor Q5 is on, which allows the BUCK node to get charged as well, through the inductor LBUCK. This occurs in the No Buck region.

When both Vboost and Vbuck reach a voltage level of 2.4 V, the Buck regulator is switched on, and the device enters the Boost-Buck region. Under control of the charge manager, the transistor Q2 connects the battery to the BOOST node, and the normal operating mode takes place. Both switching converters are active. See page 9 for Boost and Buck regulation.

As long as this normal operating mode is active, Vboost reflects Vbatt. Three voltage levels act as thresholds for the charge management state machine, described in thorough details below. If Vboost decreases below the OverDischarge level, a shutdown occurs. When Vboost reaches the ChargeReady level, the LDO regulators are activated. If Vboost increases above the OverCharge level, a mechanism is triggered to prevent further voltage increase, as materialized by the Top Voltage region.

The type of storage element in use dictates the value of the three thresholds, to obtain optimal performance and maximal protection. In addition, the lower threshold should be chosen high enough to ensure proper operation of the high voltage LDO regulator, as it is fed by the BOOST node.

CONFIGURATION

Four voltage levels can be selected to fit the application needs, namely: - The OverDischarge threshold

- The ChargeReady threshold

- The OverCharge threshold

- The voltage provided at HVOUT

In the built-in configuration mode, four combinations of these voltage levels are hardwired and selected through the CFG0 and CFG1 configuration pins, covering most application cases.

A custom configuration mode is possible, as instructed by CFG2.

CFG2 High Built-in Configuration Mode CFG2 Low Custom Configuration Mode

Table 6 - Usage of CFG2

Customizing the threshold levels involves a resistor ladder (R1 to R4) connected to BOOST and feeding SET_OVCH, SET_CHRDY and SET_OVDIS, as shown in the functional block diagram.

Customizing the voltage at HVOUT involves two resistors (R5 and R6) feeding FB_HV, the feedback node of the low voltage LDO regulator, as shown in the functional block diagram.

In addition, a dedicated configuration pin SELMPP is provided to select the MPP tracking mode suitable for the type of energy harvester in use.

CHARGE MANAGEMENT STATE MACHINE

Figure 5 - Charge Management State Diagram

The diagram above shows in details the sequencing of the charge manager as a function of the changes in Vboost.

STARTUP MECHANISM

When the energy contained in the storage element is exhausted and there is no available energy to be harvested, the AEM10940 is down. It will recover operation through a very efficient cold start engine.

A tiny power of 11 µW under just 380 mV is enough to trigger this engine, which charges CBOOST and CBUCK

up to a voltage level of 2 V, leveraging a proprietary voltage step-up charge pump.

When Vboost reaches 2 V, as indicated in the state diagram, the charge manager enters “Unloaded Voltage Rising”, completing the cold start sequence. The Boost converter gets enabled, which rises further the voltage on BOOST. All loads are maintained inactive, including the storage element.

The battery will not be shorted to the BOOST node until Vboost reaches the OverCharge level. In the diagram, this corresponds to the transition to “Connecting Storage Element”.

Cold Start

Vboost > 2 V

Vboost > Vtop+ Vboost > Vchrdy

Vboost > Vtop+

Vboost < Vtop-

After Tcrit(600 ms)

Vboost < Vovdis

UnloadedVoltage Rising

• Battery DISCONNECTED• Boost Converter ON• LV LDO Regulator OFF• HV LDO Regulator OFF• LOBATT pin status LOW

ConnectingStorage Element

• Battery CONNECTED• Boost Converter ON• LV LDO Regulator OFF• HV LDO Regulator OFF• LOBATT pin status LOW

NormalOperation

• Battery CONNECTED• Boost Converter ON• LV LDO Regulator ON• HV LDO Regulator AVAILABLE• LOBATT pin status LOW

EnteringShutdown

• Battery CONNECTED• Boost Converter ON• LV LDO Regulator ON• HV LDO Regulator AVAILABLE• LOBATT pin status HIGH

Top Voltage Operation

• Battery CONNECTED• Boost Converter OFF• LV LDO Regulator ON• HV LDO Regulator AVAILABLE• LOBATT pin status LOW

Data Sheet AEM10940


At that moment, the BOOST node reflects the battery voltage, and the charge manager checks that Vboost is above the ChargeReady level. This is normally not the case, as the starting point was a cold start or a shutdown.

Once Vboost exceeds Vchrdy, the battery is considered as sufficiently charged to support system operation, and “Normal Operation” takes place. Both LDO regulators are able to supply power to the loads.

OVERVOLTAGE PROTECTION

To prevent damage to the battery and to the internal circuitry when the charge is complete, the charge manager maintains Vboost between Vtop+ and Vtop-. This small voltage range comes from a hysteresis assigned to the OverCharge threshold. This is indicated in the state diagram as a toggling between the two rightmost states. In “Normal Operation”, the Boost converter is enabled and feeds the BOOST node, charging the battery. In “Top Voltage Operation”, the converter is disabled, and the voltage drops due to the load consumption.

SHUTDOWN MECHANISM

To prevent deep discharge leading to damage to the battery and malfunction of the high voltage LDO regulator, the charge manager takes an emergency action when Vboost drops below Vovdis. This is indicated in the state diagram as a transition from “Normal Operation” to “Entering Shutdown”. Both LDO regulators remain enabled. This allows a microcontroller powered by LVOUT to get interrupted by the low-to-high transition of the status output LOBATT, and take all appropriate actions before power shutdown.

An internal timer counts down a delay of at least 400 ms (Tcrit) before determining a state transition to “Unloaded Voltage Rising”, where the battery is disconnected and the LDO regulators are disabled. At this point, the BOOST node is completely unloaded, giving to the Boost converter the opportunity to collect energy from the source and restore the required voltage.

MPP AND BOOST CONVERTER REGULATION

Except during cold start and in the “Top Voltage Operation” condition, the Boost converter is activated. The regulation of the Boost converter involves a reference voltage Vmpp issued by the MPP internal module.

It is known that the energy source (PV cell) should be operated at a precise point in its I/V curve in order to deliver the maximum power. This is the Maximum Power Point (MPP) of the source.

Vmpp is the voltage level of the MPP, and depends on the current level of illumination of the PV cell. The MPP module evaluates Vmpp as a given fraction of Voc, the open circuit voltage of the source. By temporarily disconnecting the source with Q1, the MPP module gets and maintains a knowledge of Vmpp. This sampling occurs regularly.

Except during this sampling process, the voltage across the source, Vsrc, is continuously compared to Vmpp. When Vsrc exceeds Vmpp by 25 mV, the Boost converter

is switched on, extracting electrical charge from the source and lowering its voltage. When Vsrc falls below Vmpp by 25 mV, the Boost converter is switched off, allowing the harvester to accumulate new electrical charges into CSRC, which restores its voltage.

In this manner, the Boost converter regulates its input voltage so that the electrical current (or flow of electrical charge) that enters the Boost converter yields the best power transfer from the harvester in any ambient conditions.

The AEM10940 supports any Vmpp level in the range 0.1 V to 1.3 V. It provides a choice among two values for the fraction Vmpp/Voc through the configuration pin SELMPP.

SELMPP Vmpp/Voc Application High 90 %

PV Harvesting Low 80 %

Table 7 - Usage of SELMPP

BUCK CONVERTER REGULATION

The Buck converter charges CBUCK from the BOOST node. As long as Vboost is below 2.4 V, the transistor Q5 is turned on so that the BOOST and BUCK pins are effectively shorted. Once Vboost rises above 2.4 V, the Buck converter is enabled in switching mode. It starts transferring charges to CBUCK when Vbuck falls below 2.175 V until it reaches 2.225 mV. Then the converter stops, leaving CBUCK delivering power to the load until Vbuck drops back to 2.175 V.

LOW VOLTAGE OUTPUT

The load connected to the LVOUT output (typically a microcontroller) is supplied by the low voltage LDO regulator at 1.8 V. The maximum deliverable current is 10 mA.

The regulator operates only when the LV LDO Regulator is ON, as reported in the charge management state machine (page 8).

Upon enabling the regulator, the CLV decoupling capacitor is first preloaded to 1.8 V to avoid large inrush current. After preload, the LVRDY status pin is asserted, which can be used by the load as a power-good signal.

HIGH VOLTAGE OUTPUT

The load connected to the HVOUT output (typically a radio transceiver) is supplied by the high voltage LDO regulator at a selectable voltage. In the built-in configuration mode, an output voltage of 2.5 V or 3.3 V can be chosen. In the custom configuration mode, any value from 2.2 V to (Vbatt – 0.3 V) is possible. The maximum deliverable current is 80 mA.

The high voltage output can be deliberately enabled or disabled with the logic control pin ENHV. However, the regulator can only operate when it is available, as reported in the charge management state machine (page 8).

Upon enabling of the regulator, the CLH decoupling capacitor is first preloaded to its target voltage to avoid large inrush current. After preload, the HVRDY status is asserted, which can be used by the load as a power-good signal.

Data Sheet AEM10940


APPLICATION INFORMATION

BUILT-IN CONFIGURATIONS

The pins CFG2, CFG1 and CFG0 are configuration logic inputs that have to be tied to GND (logic Low) or BUCK (logic High). They cannot be left floating. The configuration is not intended to be switched during operation. The table below summarizes the configuration options.

Configuration pins Charge Management Threshold Voltages High voltage Output Voltage

Typical use CFG2 CFG1 CFG0 OverCharge ChargeReady OverDischarge

High

Low Low 4.50 V 3.92 V 3.00 V 2.50 V Capacitor, Supercapacitor Low High 4.12 V 3.67 V 3.00 V 2.50 V Li-Ion cell, 2.5 V radio High Low 4.12 V 4.05 V 3.60 V 3.30 V Solid State battery High High 4.12 V 3.67 V 3.60 V 3.30 V Li-Ion cell, 3.3 V radio

Low Low Low As per R1, R2, R3, R4 As per R5,R6 Custom usage

Low Low High

Reserved for future revisions of the component. Do not set the configuration to these combinations.

High Low High High

Table 8 - Usage of CFG2, CFG1, CFG0

When predefined configuration is selected (CFG2 High), the resistor pins dedicated to custom configuration should be left floating (SET_OVDIS, SET_CHRDY, SET_OVCH, FB_HV).

CUSTOM CONFIGURATION

When custom configuration is selected (CFG2 Low), all six configuration resistors must be wired as follows:

Figure 6 - Custom Configuration Resistors

They establish the customized voltages as follows:

OverCharge Vovch R1 + R2 + R3 + R4

R1

ChargeReady Vchrdy R1 + R2 + R3 + R4

R1 + R2

OverDischarge Vovdis R1 + R2 + R3 + R4

R1 + R2 + R3

HV output Vhv R5 + R6

R5

Table 9 - Customization: Resistors to Voltages

The resistor ratios are directly interpreted in Volts because the internal voltage reference of the chip is exactly 1 Volt.

In addition, the resistors should have high values to make the additional power consumption negligible. The recommended values should be such that:

• 1 MΩ < R1 + R2 + R3 + R4 < 100 MΩ • 1 MΩ < R5 + R6 < 30 MΩ

The threshold voltages Vovch, Vchrdy and Vovdis are chosen to optimize and secure the operation of the energy storage element. The output voltage Vhv is chosen to fulfill the need of the HV load. Additionally, the following constraint holds:

• Vovdis ≥ Vhv + 0.3 V

To compute the resistance values, use the following procedure:

Choose RT as the sum of R1, R2, R3, R4

R1 = RT(1

Vovch) R2 = RT(

1

Vchrdy−

1

Vovch)

R3 = RT(1

𝑉𝑜𝑣𝑑𝑖𝑠−

1

Vchrdy) R4 = RT(1 −

1

Vovdis)

Choose RV as the sum of R5, R6

R5 = RV(1

Vhv) R6 = RV(1 −

1

Vhv)

Table 10 - Customization: Voltages to Resistors

AEM10940-QFN24

HVOUT

FB_HVHV

Load

BOOST

SET_CHRDY

SET_OVDIS

SET_OVCH

GND

CFG2

CFG1

CFG0R4

R3

R2

R1

R6

R5

CBOOST

CHV

Data Sheet AEM10940


POWER GATING

The HV power supply output can be enabled or disabled through the control pins ENHV. Never leave ENHV in an undetermined state.

The table below shows two possible static power schemes:

ENHV HV output LV output

Connected to BUCK

Enabled Enabled

Connected to GND

Disabled Enabled

Table 11 – Static Power Schemes

If enabled, the HV output delivers a voltage when its LDO regulator is marked as AVAILABLE in the state diagram of figure 6.

The LV output delivers a voltage when its LDO regulator is marked as ON in the state diagram of figure 6.

The following scheme implements a dynamic control of the HV power supply:

Figure 7 - Power Gating Scheme

The LV subsystem is enabled upon startup, and can switch the HV subsystem on or off.

ENERGY SOURCE INFORMATION

The energy source must be able to supply the average power required by the loads and the AEM10940 in order to replace a battery as a primary energy source. The storage element (a rechargeable battery or a supercapacitor) supplies power when the source works below the system power requirement, and gets recharged when the source works above. The design engineer should carefully analyze all power aspects of the application to determine the features of the energy harvester.

To wake up from a deep shutdown condition, the AEM10940 requires the source to deliver a minimum of 11 µW at 380 mV to trigger and maintain the cold start mechanism. However, when internal regulators are working normally, and that the storage element is sufficiently charged to supply the loads, the source voltage may drop down to 100 mV.

The voltage level supplied by the source during harvesting should not exceed 2.5 V, even during MPP sampling.

The AEM10940 is designed to accommodate any DC energy source with a maximum power point (MPP) close to 50% or 75% of the source open circuit voltage.

STORAGE ELEMENT INFORMATION

The energy storage element of the AEM10940 can be a rechargeable battery, a supercapacitor or a large capacitor (more than 100 µF).

It should be chosen so that its voltage does not fall below the OverDischarge threshold even during occasional peaks in the load current. If the internal resistance of the storage element cannot sustain this voltage limit, it is advisable to increase the value of the CBOOST capacitor above 10 µF, or to buffer the battery with a capacitor.

The pin BATT that connects the storage element must never be left open. If the application expects a disconnection of the battery (e.g. because of a user removable connector), the PCB should provide a capacitor of at least 47 µF bypassing BATT to GND.

EXTERNAL INDUCTORS INFORMATION

By design, the AEM10940 is designed to operate with two standard miniature inductors of 10 µH.

Other inductance values are allowed, provided a minimum of 4 µH is satisfied.

Inductors must sustain a peak current of at least 150 mA. Low equivalent series resistance (ESR) is in favor of the power conversion efficiency of the Boost and Buck converters.

EXTERNAL CAPACITORS INFORMATION

By design, the AEM10940 is designed to operate with five identical standard miniature ceramic capacitor of 10 µF. The capacitor leakage should be small, as leakage currents directly impact the quiescent current of the subsystem.

CSRC This capacitor acts as a small energy tank for the energy source. It prevents large voltage fluctuations while the Boost converter is switching. The recommended minimum value is 10 µF.

CBOOST and CBUCK These capacitors act as energy buffers for the Boost and Buck converters respectively. They also reduce the voltage ripple induced by the current pulses inherent to the switched mode of the converters. The recommended minimum value is 10 µF.

CHV and CLV These capacitors ensure a good load regulation of the high voltage and low voltage LDO regulators. Closed-loop stability requires the value be in the range 8 µF to 14 µF.

AEM10940

HVOUT

CLV LV Load

Vlv

LVOUT ENHV

CHV HV Load

Vhv

Data Sheet AEM10940


TYPICAL APPLICATION CIRCUITS

EXAMPLE CIRCUIT 1

Figure 8 - Example Application 1

This circuit uses a built-in configuration scheme. It is typical of systems that use standard components for radio and energy storage.

The energy source is a photovoltaic cell, and the storage element is a standard Li-Ion battery cell. The radio communication makes use of a transceiver that operates from a 2.5 V supply.

The built-in configuration corresponding to that use case is [CFG1=Low, CFG0=High]. The resulting built-in voltages are as follows:

OverCharge Vovch 4.12 V ChargeReady Vchrdy 3.67 V

OverDischarge Vovdis 3.00 V HV output Vhv 2.50 V

Table 12 - Threshold Voltages, Example 1

The pin SELMPP is tied to BUCK (logic High), selecting an MPP ratio of 90 %, suitable for the particular PV cell in use.

Upon startup, the microcontroller is enabled, as it is supplied by the low voltage regulator, which is always ON. The application software can enable or disable the radio transceiver with the GPIO connected to ENHV.

It happens that the battery is connected with a cable that can be possibly unplugged. Therefore, a 47 µF capacitor (CBATT) is provided.

EXAMPLE CIRCUIT 2

Figure 9 - Example Application 2

This circuit uses the custom configuration scheme. It is usually required for systems that use specific components for radio and/or energy storage.

The energy source is a photovoltaic cell, and the storage element is a supercapacitor. The radio communication makes use of a transceiver that operates from a 2.7 V supply.

The configuration pin CFG2 is tied to GND, determining the custom configuration. Note that the pins CFG1 and CFG0 are also tied to GND, as recommended.

All six customization resistors are connected. With the values shown in the diagram, resulting voltages are as follows:

OverCharge Vovch 4.49 V ChargeReady Vchrdy 3.23 V

OverDischarge Vovdis 3.01 V HV output Vhv 2.69 V

Table 13 - Threshold Voltages, Example 2

The pin SELMPP is tied to GND (logic Low), selecting the MPP ratio of 80 %, suitable for the particular PV cell in use.

Upon startup, both the microcontroller and the radio transceiver are enabled. The low voltage regulator (supplying the microcontroller) is always ON. The high voltage regulator (supplying the radio transceiver) is ON because ENHV is connected to BUCK.

Li-Ion Battery

AEM10940-QFN24

BATT

HVOUT

LVOUTVlv = 1.8 V

Vhv = 2.5 V

PV Cell

SWBUCK

BUCK

BUFSRC

SWBOOST

LBOOST

10 µH

BOOST3.00 V < Vboost < 4.12 V

0.1 V < Vsrc < 2.5 VSRC

CBOOST

10 µFLBUCK

10 µH

CSRC

10 µF

CBUCK

10 µF

CHV

10 µFRadio

Transceiver3V0 Supply

VDD

Vss

CFG0

CFG1

SELMPPVbuck

=2.2 V

ENHV

HVRDY

LVRDY

LOBATT

CLV

10 µFMicro-

Controller1V8 Supply

VDD

Vss

GPIO

CBATT

47 µF

GNDSTONBATT NC

SET_OVDIS SET_CHRDY SET_OVCH

FB_HV

CFG2

AEM10940-QFN24

SET_OVDIS

SET_CHRDY

SET_OVCH

BUFSRC SWBOOST

BATT

Vhv = 2.7 V

R6 22 MΩ

R5 13 MΩ

R112 MΩ

R24.7 MΩ

R31.2 MΩ

R436 MΩ

SWBUCK

BUCK

BOOST

SRC

CBOOST

10 µF

LBUCK

10 µH

CBUCK

10 µFCFG0

CFG1

SELMPP

Vbuck=

2.2 VENHV

CFG2

CHV

10 µF

RadioTransceiver

2V7 Supply

VDD

Vss

HVOUT

FB_HV

LVOUTVlv = 1.8 V

HVRDY

LVRDY

LOBATT

CLV

10 µF

SuperCapacitor

LBOOST

10 µHCSRC

10 µF

3 V < Vboost < 4.5 V

Micro-Controller1V8 Supply

VDD

Vss

GPIO

STONBATT NCGND

PV Cell

0.1 V < Vsrc < 2.5 V

Data Sheet AEM10940


PERFORMANCE DATA

STARTUP TIMING DIAGRAM

Figure 10 - Startup Timing

SHUTDOWN TIMING DIAGRAM

Figure 11 - Shutdown Timing

100 msTime

0 ms 200 ms 300 ms 400 ms

BOOST

BATT

SOURCE

LVOUT

LVRDY

1. SOURCE connected2. Cold Start3. Boost Converter enabled4. Buck Converter enabled

5. BOOST shorted to BATT6. LVOUT precharge7. LVRDY active

2

70 V

1 V

2 V

3 V

4 V

5 V

6 V

1 sTime

0 s 2 s 3 s 4 s

BOOST

BATT

SOURCE

LVOUT

LVRDY

1

1. SOURCE disconnected2. BATT falls below OverDischarge

3. LVOUT disabled BATT disconnected from BOOST4. Buck Converter disabled

LOBATT

0 V

1 V

2 V

3 V

4 V

5 V

6 V

Data Sheet AEM10940


BOOST CONVERSION EFFICIENCY

Figure 12 - Boost Efficiency at 2.8 V



LOW VOLTAGE CONVERSION EFFICIENCY (INCLUDES LDO AND BUCK CONVERTER)

Figure 15 - LV efficiency versus battery voltage

Figure 16 - LV Efficiency versus output current

LOW VOLTAGE LDO LOAD REGULATION HIGH VOLTAGE LDO LOAD REGULATION

Figure 17 - LV LDO Load Regulation

Figure 18 - HV LDO Load Regulation

ηBOOST

100 %

80 %

40 %

20 %

0 %

0.00 V 0.25 V 0.50 V 0.75 V 1.00 V 1.25 V

Vboost = 2.8 V

Iscr = 100 µA

Isrc = 1 mA

Iscr = 10 mA

0.00 V 0.25 V 0.50 V 0.75 V 1.00 V 1.25 V

ηBOOST

100 %

80 %

40 %

20 %

0 %

Vboost = 3.6 V

Iscr = 100 µA

Isrc = 1 mA

Iscr = 10 mA

ηBOOST

100 %

80 %

40 %

20 %

0 %

0.00 V 0.25 V 0.50 V 0.75 V 1.00 V 1.25 V

Vboost = 4.1 V

Iscr = 100 µA

Isrc = 1 mA

Iscr = 10 mA

ηLV

100 %

80 %

40 %

20 %

0 %

2.75 V 3.00 V 3.25 V 3.50 V 3.75 V 4.00 V 4.25 V 4.50 V

Ilv = 100 µA

Ilv = 1 mA

Ilv = 10 mA

ηLV

100 %

80 %

40 %

20 %

0 %

1 µA 10 µA 100 µA 1 mA 10 mA

Vbatt = 3.0V

Vbatt = 3.6 V

Vbatt = 4.1 V

1 µA 10 µA 100 µA 1 mA 10 mA

Vbatt = 3.6 V

Vlv

1.77 V

Vbatt = 3.6 V

Vhv

2.90 V

1 µA 10 µA 100 µA 1 mA 10 mA 100 mA

Data Sheet AEM10940


PACKAGE INFORMATION

PLASTIC QUAD FLATPACK NO-LEAD (QFN24 5X5MM)

R 0.15

1

24

3.65 ± 0.10

3.65

± 0

.10

0.30 ± 0.05

0.65 BSC

0.40 ± 0.05

0.40

± 0

.05

0.40 ± 0.05

3.25 REF

5.00 ± 0.10

5.00

± 0

.10

0.90 ± 0.10

0.2 REF

0.02 + 0.03- 0.02

Data Sheet AEM10940


BOARD LAYOUT

3.25

± 0

.05

0.375 ± 0.05 0.825 ± 0.05

0.65 BSC

3.60 ± 0.05

3.60

± 0

.05

5.75

± 0

.05

4.10

± 0

.05

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