EEWeb Pulse - Issue 58, 2012

7/31/2019 EEWeb Pulse - Issue 58, 2012

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PULSE

EEWeb.c

Issue

August 7, 20

Bill HallSenior Vice President

ON Semiconductor

Electrical Engineering Commun

EEWeb


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TABLE OF C ONTENTS

Bill Hall 4ON SEMICONDUCTOR

Featured Products 9

BY ALEXEI ZERNOV, YNGVE WERNQVIST & CHRIS YOUNG WITH INTERSIL

BY MARTIN TOMASZ WITH TOUCHSTONE SEMICONDUCTOR

RTZ - Return to Zero Comic 20

Interview with Bill Hall - Senior Vice President & General Manager of the Standard Products Group

Why digital power solutions are becoming more widespread for their advantages in powerconversion and efficiency.

How analog op amps support always-on circuitry around the microcontroller offering thebest low-power solution.

11Digital Power Solutions Offer Performance

and Integration Enhancement

16Using Analog Components to Manage

Power in Low-Power Solar Systems



INTERVIEW

at that time with a Co-op program.This allowed me to work full-time 6

months of the year while getting aBSEE. I co-opd at RCA Missile and

Surface Radar Division and got todo cool things like write software for

a missile flight simulator along withsome mundane jobs like peeling

Rubylith. I eventually graduatedfrom Drexel in 1980 and took a full

time job with RCA.

How did you get into electricalengineering and when didyou start?

I actually got my start by mowing

the lawn at an electronics distributorwhen I was in high school in the early

70s. I was eventually offered a part-time job in the warehouse. When I

graduated from high school, themanager of the warehouse offered

me a full time job at $135/wk. SinceI had no idea what I wanted to do

in life, I took the job with the goalof working my way into sales. After

2 years of being told I was more

valuable in the warehouse then insales, I decided it was time to go

to college. During my time at thedistributor, I had contact with many

Electrical Engineers. They seemedreally smart and drove nice cars and

since I was good at math, I decidedto become an Electrical Engineer.

In addition to starting college in

1975, I also got married, whichmeant I needed a source of income.

I decided to pick Drexel Universityin Philadelphia because they were

one of the few schools in the country

Bill

HallON Semiconductor



INTERVIEW

Can you tell us more aboutyour work experiencebefore you started at ONSemiconductor?

My first job was with RCA as a

RADAR Design Engineer. I workedon a RADAR digital signal processor

for 5 years. We began by designingthe system on paper, pretty muchusing discrete Logic ICs along

with some EEPROMs and somebit slice micro-processors. The

design was at the module level,so, for example, one module was

a complex arithmetic multiplier,another was a target detector and

so on. This was cool stuff becausewe actually used mathematics that

you thought were just in textbooks,like real and imaginary numbers,

Eulers Theorem, and RADARcountermeasures techniques.

After the design was complete, wesimulated the modules in FORTRAN

and eventually manufacturedthe modules and began test and

integration. Test and integration

lasted years and involved rotatingshift work since these modules wereinstalled in a commissioned navy

ship (actually just a conning tower)in the middle of a corn field in New

Jersey. Eventually, the changingshifts got old and I went to work for

Fairchild Semiconductor in Maine.

I was hired as an applications

engineer, but on my 1st day ofwork, my boss asked if I would be

willing to be a marketing engineerfor 3 months then I could go back

to applications engineering. I said,if the pay is the same, no problem

even though I had no idea whatmarketing did. I actually found that I

liked marketing because you got tomake a lot of strategic decisions. So

after 3 months, I stayed in marketing

and began to climb the ladder,working through various manager

positions. Marketing exposed me tomany aspects of the business, but

the next step I wanted was to run a

business. In 1987 Fairchild was soldto National and I took

In the near future,

we can expect to

see wide band gap

technologies, muchmore use of integrated

passive components

in filtering, oscillators

and RF amplification.

Also, advances in

chip singulation willincrease the number of

die per wafer without

changing lithography.

on several Product Line Director

positions. I liked running product

lines because you were essentiallyrunning a small company within alarger company. In these positions

I was responsible for marketing,product development, design,

product engineering, applicationsengineering, supply chain, and all

the financial aspects of the P&L.It was real easy to tell if you were

doing a good or bad job, just lookat the P&L.

National Semiconductor spun

off Fairchild in 1997 and I stayed

with Fairchild, so I worked for 3companies in the space of 10 yearsand never changed my phone

number. I kept getting more andmore product lines folded into my

group and got promoted to VicePresident of the Interface & Logic

Group in 1999 and eventuallycreated and co-ran the Standard

Products Group in 2004.

In 2006 I moved from Fairchild in

Maine to ON Semiconductor inPhoenix as Senior VP & GM of the

Standard Products group. As theysay; its a dry heat.

What have been some of yourinfuences that have helpedyou get to where you aretoday?

My father instilled a good set ofvalues and a good work ethic in me.

The warehouse manager that Iworked for taught me not to worry

about what other people are doingjust focus on doing the best job you

can and cream always rises to thetop.

Do you have any tricks upyour sleeve?

Somebody once told me that if you

are an engineer, you can do almostany job that is out there, which has

worked for me. In my career, I havebeen a radar design engineer,

a semiconductor applicationsengineer, a marketing engineer, a

product engineer, and have hadmanagement jobs with finance,

quality, HR, supply chain and



INTERVIEW

engineering functions reporting into

me. All of these functions came witha learning challenge but kept life

interesting.

What has been your favoriteproject that youve workedon?

My favorite engineering project wasdesigning anti-counter measures

hardware for a naval radar. I had toimplement algorithms in hardware

for target detection in a jammingenvironment, or detecting a target

in cloud cover, or telling a targetfrom a fake pulse that the target

broadcasts back to you. Its a verycreative process and these modules

that you design are like children.

Do you have any note-worthyengineering experiences?

One experience that stands out waswhen I first moved to Fairchild in

1985 and became the Marketing

Manager for ACMOS Logic. Wewere launching the FACT family(Fairchild Advanced CMOS

Technology). A large competitorin Texas who shall remain un-

named was late to market withtheir technology and made a big

deal of the noise characteristics(ground bounce) in FACT. Lots of

the marketing people at Fairchildsaid dont acknowledge the

competitors claims and the issue

would go away, but since I hadrecently been a system designengineer I was pretty sure the issue

wouldnt go away and our slowsales ramp was proving that true. I

began to tear down the competitorscase one issue at a time. Things

like noise in a lumped load test jig

doesnt simulate noise in a real

The trick to devices

getting smaller is more

power dissipation in a

smaller surface area.

The trick to power

efficiency is in complexsemiconductor

processes and

techniques that

facilitate faster

switching speeds.

system with distributed loads andonly specific signals in a digital

system would be affected by thisnoise and so on. I created a demoboard that showed these factors

and travelled around the world withan oscilloscope (and they were

pretty big in 1985) and showedsmall groups of engineers the truth

that this was a good technology, ifyou take the proper precautions.

Again, having just left the designcommunity I knew design engineers

dont believe marketing hype and itwas critical to show real waveforms

in a live demo environment. Thisworked and FACT went on to be a

good revenue generator for many

years.

What are you currentlyworking on?

My group is focussing on HighPerformance Power Discretes

(IGBTs, MOSFETs, Rectifiers) andcutting edge Protection devices

like ESD and EMI Filters. We havethe industrys first silicon Common

Mode Filter. Also, packaging isreal important from CSP to high

power density packages and IPMs

(Intelligent Power Modules fromour Sanyo acquisition).

Can you tell us more aboutON Semiconductor andthe technology they aredeveloping?

Most of ON Semiconductor is fo-cused on power efficiency: every-

thing from power switching, powercontrol, and power management to

low power consumption.

We are working on LED Drivers andESD protection for LED general

lighting.

In the automotive realm we areworking on sensors for lanedeparture and vehicle positioning,

extreme high temperaturecontrollers for in transmission &

on engine applications and voltageregulation for infotainment & driver

information.

In computing and wireless: cuttingedge power management for

that increases power efficiencyand decreases power density.

For example: we are developing



INTERVIEW

technology for power supplies thatwill have less than 10mW of power

loss in standby mode.

Other areas include power

conversion for high end powersupplies and motor control forindustrial applications. We are

also adopting technology thatwas developed for hearing aids to

provide high quality audio output forcell phones.

On the packaging side we areworking on chip scale packaging

which reduces the volume of adiode by more than 99% from the

most common SMT packages usedtoday.

What direction do you seeyour business heading in thenext few years?

One trend that I am seeing in the

industry is that everything is gettingsmaller and more power efficient.

The trick to devices getting smalleris more power dissipation in a

smaller surface area. The trickto power efficiency is in complex

semiconductor processes and

techniques that facilitate fasterswitching speeds.

What are some newtechnologies we can expectto see from ON Semiconductorin the near future?

In the near future, we can expect to

see wide band gap technologies,much more use of integrated

passive components in filtering,

oscillators and RF amplification.Also, advances in chip singulationwill increase the number of die per

wafer without changing lithography.

What challenges do youforesee in our industry?

The business cycles are gettingshorter and more pronounced,

supply chains are getting verycomplex, and it is getting harder

and harder to squeeze the cost outof the products.

What are some of yourhobbies outside of work anddesign?

Having lived in Maine, I must saythat my biggest hobby is fishing. I

have a vacation home on the coastand I like to go offshore fishing fortuna and sharks.

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FEATURED PRODU CTS

30V, Micropower, Over-voltage Protection

The ADA4096-2 dual and ADA4096-4 quad operational amplifiers feature

micropower operation and rail-to-rail input and output ranges. Theextremely low power requirements and guaranteed operation from 3 V

to 30 V make these amplifiers perfectly suited to monitor battery usageand to control battery charging. Their dynamic performance, including

27 nV/Hz voltage noise density, recommends them for battery-powered

audio applications. Capacitive loads to 200 pF are handled without

oscillation. For more information, please click here.

High Performance Micro 20-Lead LFCSP

The ADP5041 combines one high performance buck regulator and

two low dropout regulators (LDO) in a small 20-lead LFCSP to meetdemanding performance and board space requirements. The high

switching frequency of the buck regulator enables use of tiny multilayerexternal components and minimizes board space. When the MODE pinis set to logic high, the buck regulator operates in forced PWM mode.

When the MODE pin is set to logic low, the buck regulator operatesin PWM mode when the load is around the nominal value. When the

load current falls below a predefined threshold, the regulator operatesin power save mode (PSM), improving the light load efficiency. For more

information, please click here.

High Accuracy Temperature Monitor

The LTC2996 from Linear Technology Corporation measures a remotediodes temperature with 1C accuracy and its own die temperature with

2C accuracy while rejecting errors due to noise and series resistance.The device provides a voltage-proportional-to-absolute-temperature

output, as well as individual undertemperature and overtemperaturealert outputs, defined by user-adjustable thresholds. No code is required

to configure the device. With a 200A quiescent current, the LTC2996simply provides a precise, space-saving, micropower temperature

monitoring solution. For more information, please click here.

2996BD

CT2

CT1

VTH

VREF

VTL

VPTAT

+

+

+

200k

1.2V

1.8V

400k

UVLO

8

1

2

5

4D

D

+GND

3

T TO V

CONVERTER

OT/UT

PULSE

GENERATOR

OT

VCC

400k

UT

VCC

400k

7

9

10

VCC

6

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EMI Test Receiver for Reduction of Test Times

Rohde & Schwarz introduces the new R&S ESR EMI test receiver whose

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SW

EN_BK

09652-

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FB2

R4

R4 R5

R3

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R3R7

C52.2F

C62.2F

VOUT2

AVIN

VBIAS

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VOUT1

FB1

L11H

R1

R2VIN1 = 2.3V TO

5.5V C14.7F

SUPERVISOR

P

nRSTO

WDI

VTHR

MR

RFILT = 30

VIN2 = 1.7V

TO 5.5V

VIN1

ON

OFF

ON

OFF

ON

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EN1

VIN2

C21F

C31F

EN2

EN3

VIN3VIN3 = 1.7V

TO 5.5V

EN_LDO2

LDO2(ANALOG)

BUCK

AGND

VOUT1 AT

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PGND

FPWM

PSM/PWMMODE

VOUT2 AT300mA

VOUT3 AT300mA

VOUT3

LDO1(DIGITAL)

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OUTA 1

INA 2

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V 4

+V8

OUTB7

INB6

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ADA4096-2

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TECHNICAL ARTICLE

Digital PowerSolutions Offer

Performance andIntegration Enhancement

Authors:

Alexei Zernov

Yngve Wernqvist

& Chris Young

Intersil

Introduction

Digital power is a technical termused to name a way of controlling

power conversion by using digitalsignal processing techniques. We

are in the middle of a revolutionwhere the advantages of digital

power are being applied to powerconversion and real advancements

are being made in the areas ofefficiency, power density, reliability,

robustness and ease of use.Although the first digital control

ideas are more than 30 years old,

we are just now being to see thewidespread use of this technology.

Digital Power ArchitectureEvolution

The process of regulation and

control of a switching power supplyincludes generation of a pulse

width modulated (PWM) signalwhich drives one or more power

transistors. The PWM signal is, inall switching regulators, in a sense

a digital signal. Thus, it was a

natural concept to consider a digitalcontroller for generating the PWM.

Some of the earliest digital powercontrollers used special purpose

microprocessors called digitalsignal processors (DSP) and

general purpose microcontrollers(uC). In these controllers, the

analog signal representing theoutput voltage of a regulated power

supply was digitized and the digitalsignal was then processed in the



TECHNICAL ARTICLE

DSP. While the DSPs were quite

capable in terms of processingpower, to achieve the fast processing

speeds needed for high frequencyswitching power supply control,

high clock speeds were required.The high clock speed and the

inherent high bias current requiredin those DSPs meant a significant

amount of power was consumedin the power conversion process.

Furthermore, the DSPs were tooexpensive for the switching power

supply applications. See Fig 1.

About 10 years ago, dedicated

function state machine baseddigital power controllers began to

appear, first in academia and thenin commercial offerings. These

state machines were designedspecifically to be used as digital

switching power supply controllers.Controllers contained specialized

HW peripherals for powerconversions purposes. They were

optimized to the point that digitalpower started to be economically

viable across a wide range ofapplications. This was that turning

point in the history of digital power.A block diagram of the modern

digital power converter ZL6105is shown in Fig 2. A regulation

loop key element is a special statemachine - PID Digital Compensator.

Advantages of Digital PowerArchitecture

Digital signal processingtechnology is ideally suited for

digital PWM signal generationand allows implementation of

advanced processing algorithms:filters, performance optimization

algorithms, and nonlinear controland auto-compensation. Optimized,

low power voltage setting DAC andVoltage and Current monitoring

ADCs provide telemetry facilitiesand information far advanced

compared to analog worldcontrollers. All of this enables digital

power technologies to deliver newlevels of conversion performance,

functionality and integration.

Improved Efficiency

Thanks to digital control, the Zl6105

is capable of executing algorithmsto optimize the dead-time applied

between the gate driver signalsfor the top and bottom FETs. In a

synchronous buck converter theMOSFET drive circuitry must bedesigned such that top and bottom

MOSFETs are never in conductingstate at the same time. Conversely,

a long period of time which bothMOSFTS are off reduces circuit

efficiency by allowing current toflow in their parasitic body diodes.

The ZL6105 has an algorithm thatconstantly adjusts dead-time non-

overlap to minimize losses, thusmaximizing efficiency. This circuit

will null out dead-time differences

due to components variation,temperature and loading effects.

Figure 1: Digital Power Controller Using DSP or General PurposeMicrocontroller

Figure 2: Digital Power Controller ZL6105 Using PID Digital Compensator andOptimized Set of HW Peripherals

DigitalPWM

Controller

PowerManagement

ControllerInterface

DSP+

L M N

DPWM

SDA

SCL

DriverADC

DigitalVREF

VOUT

Power Management

Input Voltage Bus

NVM

D-PWM

NLR

PLL

VTRK

SYNC

DDC

I2C

SALRTSDASDL

SA(0,1)

ADC

ADCCommunication

DACREFCN

MUX

VDD

TempSensor

VoltageSensor

MOSFETDriversPID Digital

Compensator

VOUT

FC(0,1) VDD

VR

BST

ISENBVSEN

ISENA

VSEN+

VSEN

XTEMP

SW

V(0,1)SS

CFG(0,1,2)ILIM

MGNEN

PG

+

ADC

Sync Gen



TECHNICAL ARTICLE

eliminates dozens of componentsfrom the design. Further HW

integration, and therefore reliabilityimprovement can be found in

integrated FET controllers like theZL2101 and even fully integrated

power supply modules like theZL9117. Fig 3 shows how easily two

ZL9117 modules can be combinedto build a two phase current sharing

rail.

Digital power robustness isenhanced by ability to monitor

and respond, in an optimal way,

control and monitoring. Input,output voltage and output current

monitoring allows ZL6105 todetect system faults and prevent

of catastrophic consequences

for power supply and load byconfigurable fault reaction.

Ease of Use and Auto-

CompensationStability is a critical operational

requirement for power supplies. Inregulated power supplies, stability

is controlled by the characteristicsof the feedback path. Power supply

engineers need to ensure stableoperation over all load conditions,

environmental conditions andcomponent characteristic variations.Design of the feedback loop to be

stable under all of these conditionsis a time consuming task.

Digital power solutions provide an

alternative to analog compensation.Digital compensation has no

external components and can be

tuned just by changing the gainvalues stored in digital registers.Digital filters are not simply

replacements of analog filters.Digital filters can perform functions

Integration and Reliability

Reliability is a term used to describe

the relative likelihood that a powersupply will not fail. In general, the

reliability of any system, includinga power supply, decreases with

an increase in the number ofcomponents. An advantage of

modern digital power controllers

is that they are highly integratedand require fewer componentsto achieve a full featured power

supply.

The ZL6105 digital power controller

integrates not only the powerconversion control but power

management, fault management,and telemetry. Synchronization

functions such as ramp up anddown sequencing, switching

phase spreading, current sharing,fault spreading and others are

performed using communicationvia a proprietary communication

bus. The system monitoringfrom the host is performed via

I2C interface using the industrystandard Power Management Bus

commands (PMBus). All this

to environmental changes. As anexample, the ZL6105 monitors

both the internal die temperatureand external temperatures.

This allows the controller tocompensate temperature sensitivemeasurements for accurate

that go far beyond the capabilities ofanalog filters. For example, in high

Q (>0.5) second order circuits,the poles in the plant are complex

conjugate poles which may requirecomplex conjugate zeros in thecompensation network to effectively

Figure 3: Two ZL9117 Modules Using Communication via DDC Bus for

Current Sharing

VIN

CIN

CIN

COUT

VOUT

COUT

ZL9117M

ZL9117M

DDC

3.3V to 5V

DDC



TECHNICAL ARTICLE

compensate. Conventional analog

compensators only provide realzeros for compensation. On the

other hand, digital filters can easilyprovide the complex conjugate

zeros to compensate high Q powersupplies.

Nonetheless, even this advantage,

in many cases is not enough tostabilize and optimize a power

supply over all conditions. Initialinductor and capacitor values

can vary by +/- 10% . This can

significantly change the control loopeven to the extent that the powersupply has substantially degraded

stability. For example, electrolyticcapacitor characteristics suchas the capacitance and ESR can

greatly change with temperature.What is really needed is a method

for compensating power suppliesthat is automatic.

Intersils Zilker Labs has recently

released several parts with autocompensation. All of those use

an advanced digital algorithmto characterize the plant and

to determine appropriatecompensation settings for stable

operation.

All these converters use a dedicatedstate machine for the digital PWM

controller and an embeddedmicrocontroller to monitor the

circuit, environmental conditions,

and configuration profile to setupand modify the state machineoperation in real time.

During auto-compensation, the

microcontroller adjusts the statemachine to stabilize the power

conversion process by adjustingthe compensation coefficients in a

systematic way while observing theresponse of the system. While this

does produce a slight perturbationon the output it is almost

imperceptible and well within theallowed transient envelop.

In practice, auto compensationis easy to use. Simply enable the

power supply and the controllerdoes all of the work. Fig4 shows

the transient response of a typicalpower supply before (upper) the

supply is adequately compensated.

The second trace (lower) showsthe transient response after autocompensation.

An additional benefit of automaticcompensation is that the plant is

characterized by the compensationalgorithm. The values of Gain, Q,

and Natural Frequency can bemonitored over the life of the power

supply and significant changes inthe plant can be observed, many

times, before failure of the system.This allows the user to incorporate

predictive diagnostics of the systemhealth for improved reliability.

Auto-compensation saves the

design engineer a considerable

Figure 4: Transient Respond of the PowerSupply System Before (Upper Graph) andAfter Auto Compensation (Lower Graph)

amount of time, producing amore stable power supply and

potentially improves the reliabilityand robustness of the power supply

system.

Conclusion

Digital power control offers manyadvantages over traditional analogcontrollers in terms of optimal

performance, reliability, highnumber of features, and ease of use.

Switching from traditional analogpower control to digital power

control is easy and rewarding.

About the Authors

Chris Young serves as Sr.Manager for Digital PowerTechnology at Intersil Zilker

Labs. Previously he served ChiefTechnical Officer for Zilker Labs.

He has over 20 years of experiencein the management of research

and development of state of the artelectronic systems. He was one of

the founders and vice presidentof technology at ColdWatt, Inc.

Prior to that, he held technical andengineering management positions

at leading companies includingDell, Astec Power, Lucent/Bell Labs

and Unison Industries. He has hadnumerous publications and patents

in the areas of pulsed power,power control and conversion,

and stability analysis. Mr. Youngholds Bachelors degree in Physics

from the University of Texas anda Masters degree in Electrical

Engineering from Texas TechUniversity where he also serves on

the Industrial Advisory Board.


15/20

1.8V to 3.3V, Micro-Power, 15kV ESD, +125C, SlewRate Limited, RS-485/RS-422 Transceivers

ISL32600E, ISL32601E, ISL32602E, ISL32603EThe Intersil ISL32600E, ISL32601E, ISL32602E and

ISL32603E are 15kV IEC61000 ESD protected, micro power,

wide supply range transceivers for differential communication.

The ISL32600E and ISL32601E operate with VCC 2.7V and

have maximum supply currents as low as 100A with both the

transmitter (Tx) and receiver (Rx) enabled. The ISL32602E and

ISL32603E operate with supply voltages as low as 1.8V. These

transceivers have very low bus currents, so they present less

than a 1/8 unit load to the bus. This allows more than 256

transmitters on the network, without violating the RS-485

specifications 32 unit load maximum.

Rx inputs feature symmetrical switching thresholds, and up to

65mV of hysteresis, to improve noise immunity and to reduce

duty cycle distortion in the presence of slow moving inputsignals. The Rx input common mode range is the full -7V to

+12V RS-485 range for supply voltages 3V.

Hot Plug circuitry ensures that the Tx and Rx outputs remain in

a high impedance state while the power supply stabilizes.

This transceiver family utilizes slew rate limited drivers, which

reduce EMI, and minimize reflections from improperly terminated

transmission lines, or unterminated stubs in multidrop and

multipoint applications.

The ISL32600E and ISL32602E are configured for full duplex

(separate Rx input and Tx output pins) applications. The half

duplex versions multiplex the Rx inputs and Tx outputs to allow

transceivers with output disable functions in 8 Ld packages.

Features Single 1.8V, 3V, or 3.3V Supply

Low Supply Currents . . . . . . . ISL32601E, 100A (Max) @ 3V

. . . . . . ISL32603E, 150A (Max) @ 1.8V

- Ultra Low Shutdown Supply Current . . . . . . . . . . . . . . 10nA

IEC61000 ESD Protection on RS-485 I/O Pins . . . . . . 15kV

- Class 3 ESD Levels on all Other Pins. . . . . . . . . >8kV HBM

Symmetrical Switching Thresholds for Less Duty Cycle

Distortion

Up to 65mV Hysteresis for Improved Noise Immunity

Data Rates from 128kbps to 460kbps

Specified for +125C Operation

1/8 Unit Load Allows up to 256 Devices on the Bus

-7V to +12V Common Mode Input/Output Voltage Range

(VCC 3V)

Half and Full Duplex Pinouts; Three State Rx and Tx Outputs

5V Tolerant Logic Inputs

Tiny MSOP Packages Consume 50% Less Board Space

Applications Differential Sensor Interfaces

Process Control Networks

Security Camera Networks

Building Environmental Control/Lighting Systems

FIGURE 1. ISL32600E AND ISL32601E HAVE A 9.6kbps

OPERATING ICC LOWER THAN THE STATIC ICC OF

MANY EXISTING 3V TRANSCEIVERS

SUPPLY VOLTAGE (V)

ICC(

A)

2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6

10

100

1m

25C, RD = , CD = 50pFDE = VCC, RE = GND

ISL3260XE STATIC

ISL3260XE DYNAMIC (9.6kbps)

ISL3172E STATIC

ISL3172E DYNAMIC (9.6kbps)

FIGURE 2. ISL32602E AND ISL32603E WITH VCC = 1.8V REDUCE

OPERATING ICC BY A FACTOR OF 25 TO 40,

COMPARED WITH ICC AT VCC = 3.3V

SUPPLY VOLTAGE (V)

ICC(

A)

100

1m

10m

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6

DE = VCC, RE = GND

STATIC

DYNAMIC (128kbps)

DYNAMIC (256kbps)

25C, RD = , CD = 50pF

June 22, 2012

FN7967.0

Get the Datasheet and Order Samples

http://www.intersil.com

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2012

All Rights Reserved. All other trademarks mentioned are the property of their respective owners.
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Using Analog

Componentsto Manage Power inLow-Power Solar Systems

Martin TomaszTouchstone Semiconductor - Senior Scientist

From large panels to harvested microwatts from a fewphotodiodes, solar power is increasingly prevalent inautonomously powered systems. With the worldwide

evolution toward lower power operation using more

green energy sources, emphasis on deploying solarpower in a greater variety of environments has been onthe rise.

In low-power solar systems, it is critical to assess whether

there is sufficient sunlight at a given time to power thesystem. In some cases, this involves determining

whether there is sufficient power to enable themicrocontroller. In many ultra-low-power systems,

the simple act of waking the microcontroller tomake a voltage measurement might collapse thesolar source or waste precious power from a

reservoir capacitor.



TECHNICAL ARTICLE

One solution is to incorporate a simple analog op ampinto the system. An ultra-low-power analog op amp can

support always-on circuitry around the microcontrollerand may be the simplest and best solution.

Ultra-Low-Power Op Amps

Figures 1 to 3 illustrate a few simple circuits using an

ultra-low-power op amp in a continuous always-onmeasurement mode assessing the state of the solar cell.

The technique hangs on using an op amp whose total

power is as low as practical driven primarily by ultra-lowsupply voltage operation.

The circuit in Fig. 1 shows a photodiode in photovoltaiczero-bias mode. The short-circuit current is measured

and converted to a voltage across resistor R1 while thefeedback action of the op amp forces 0 V across D1.Zero-bias photovoltaic current is a convenient parameter

that is generally well characterized and can be directlyreferenced to most photodiode manufacturer datasheets.

Note that with the rail-to-rail input range of the analog opamp, in this case Touchstone Semiconductors TS1001

op amp, the photodiode may be connected directly tothe positive supply voltage rail.

The circuit in Fig. 2 generates a simple positive-polarity

output for a similar zero-bias-mode measurement. In

Figure 1: An ultra-low power op amp can be a continuous, always-on measurement mode.

Figure 2: An ultra-low-power op amp offers simple, positive polarity output to support a zero bias condition.

Power Status

Measured Light

wait

good

lux

V

T12N3906

U1TS1001

R22.2M

R1 100k(adjust for photodiode)

C1 0.01F

C20.1F

1V-2.5V

D1photodiode

+

Measured Light

lux

V

U1TS1001

R1 100k(adjust for photodiode) C1

0.01F

C20.1F

1.8V-2.5V

D1photodiode

+



TECHNICAL ARTICLE

this case, the op amp servos its output to sink sufficient

current to support the zero bias condition for D1. This

creates a voltage across resistor R1 at the negativesupply voltage pin of the TS1001. Since this ultra-low-power op amp contributes less than 1 A to this current,

the current measured from D1 has minimal error.

For a more comprehensive assessment, the circuit in

Fig. 3 tests the solar source to see if it can handle theload. The circuit shown makes this assessment without

burdening the microcontroller and risking collapse ofthe supply during measurement.

Approximately once per 100 ms, the circuit disconnects

the solar-cell power source from its reservoir capacitorand load, applying a test load (R1) and assessing the

resulting voltage drop. If the voltage drops 25% or more,the result is latched into U2 and the power status isprovided to the microcontroller.

This ultra-low power circuit draws less than 3 A at 1V.

Op amp U1 provides the timer function and controlstransistor switches T1 and T2 to apply the test load while

simultaneously disconnecting the load. Capacitor C1

+

+

Power Source(solar cell)

Power Status

Load(uC, etc)

good

wait

C147F

R2220K

R55.1M

R5510K

R6510K

R9220K

T3BSH105

N-ch

U2TS1001

T4BSH105

N-ch

R81.4M 1% R11

220K

R7365K 1%

R10

5.1M

R31M

C210nF

R1test load

T1BSH205

P-ch

T1BSH105

N-ch

T5BSH105

N-ch

U1TS1001

Power Check

enable

disable

Figure 3: An ultra-low-power op amp-based circuit assesses a PV solar-cell source.

temporarily holds the voltage to keep this circuitry and

any standby loads powered. Op amp U2 serves as a

comparator, tripping when the power source drops morethan 25% (with 5% hysteresis). Transistor T3 latches theresult, while transistor T4 resets the latch during each

assessment period to ensure a fresh reading.

Such test loading is useful for determining the available

power from a solar cell, since merely measuring the opencircuit voltage generally does not provide an accurate

assessment.

Assessing Always-On CircuitryGenerally, an ultra-low-power op amp, like Touchstone

Semiconductors TS1001, is an excellent option forsupporting always-on analog circuitry. For example,

op amps that are guaranteed to operate under 1 V andconsume less than 1 A current may be configured as

a filter and left continually on, so that a microcontrollermaking an ADC measurement does not have to stay

powered on while the filter settles.

In conclusion, ultra-low-power op amps are useful in



TECHNICAL ARTICLE

low-power solar systems to assess the available power

from solar cells before a load is applied, and generallyto support standby, always-on circuitry, while drawing

negligible currents.

About the AuthorMartin Tomasz is principal of Touchstone Semiconductor,an engineering consulting company offering expertise in

circuit and systems design. Mr. Tomasz is a seasonedanalog and mixed signal engineer with 22 years

experience in circuit and systems design. Past experienceincludes 12 years at Maxim Integrated Circuits where he

was Senior Scientist, and Quantance, where he was VPProduct Architecture. He currently holds 12 patents.

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20/20

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EEWeb Pulse - Issue 58, 2012

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