LETTER FROM THE CEO IN-DEPTH ARTICLES

LETTER FROM THE CEO IN-DEPTH ARTICLES
Volume Sixty-Five
LETTER FROM THE CEO
2
IN-DEPTH ARTICLES
Reduce Standby Power Drains with Ultra-Low-Current, Isolated,
Pulse-Frequency-Modulated (PFM) DC-DC Converters
3
Keep Power Consumption in Check with Low-Power Comparators that
Autosense Plugged-In Accessories
8
Low-Loss LED Driver Improves a System’s Green Footprint by Boosting Efficiency
and Extending Battery Life 12
Little Things Mean a Lot
14
T1
D1
L1
R1
C1
5
C2
4
U1
V+
REF
SHDN
EXT
2
1
U2
R3
M1
R2
C3
R4
C4
6
3
MAX1771
AGND
FB
CS
GND
R6
8
C7
7
C9
R7
D2
R8
R9
C5
C6
C8
U3
R10
Schematic of an isolated PFM flyback DC-DC converter. See page 5.
R5
R11
C10
TM
Letter from the CEO
Maxim Provides Resources for Energy-Efficient Design
Recently, I calculated the energy usage of devices in my home. To my surprise, I discovered that my media server is using
$473 worth of electricity a year—that means that I spend more to operate the server over one to two years than I paid for the
server itself! I wonder if the server manufacturer is worried about this, and whether their customers are aware of this high total
cost of ownership. If the manufacturer could reduce the energy usage of this device, it would give all their customers an effective
discount. Not only would this energy efficiency reduce our impact on the environment, but it would be a competitive advantage.
This is precisely the challenge that we face as engineers. With the rising costs of energy and increased awareness of global
warming, consumers are demanding more environmentally friendly products. This demand poses complex technical challenges
for engineers, but it also represents a new business opportunity. That is, electronics manufacturers who offer higher-efficiency
products will have a competitive advantage in today’s marketplace.
When you think about it, this new emphasis simply rewards designers for good engineering. Even before “green” became a
byword, low-power design was good design. Greater power efficiency means smaller power supplies, lower costs, greater board
densities, improved battery life, reduced heat, and higher reliability.
In the past, efficiency was one of several parameters that engineers traded off to meet customer needs. However, with the
energy challenges facing our world today, efficiency is a tradeoff that we can no longer afford to make.
Maxim has designed “green” products for over 25 years. You know us as leaders in high-efficiency DC-DC converters,
battery-management ICs, and low-power products such as amplifiers. And, of course, we have been working for years to make
our products lead-free and reduce the use of hazardous materials.
You can count on Maxim to deliver innovative, energy-efficient solutions. We are devoting more engineering resources to
exciting, environmentally friendly technologies, in addition to the ones that we already pioneered. Specifically, we are applying
our expertise to hybrid automotive, solar power conversion and control, high-brightness LEDs, display drivers, notebook power,
and many other new areas.
We are also reorganizing our website to make it easier to find green design resources. Over the years, we have written over
2000 application notes, many of which can help you improve the efficiency of your products. We have assembled these and other
design resources on one easy-to-use microsite: www.maxim-ic.com/green-design.
Our engineers will continue to provide new design tips, reference designs, and application notes to help you maximize
efficiency. Stay tuned to Maxim’s website for technical information and products that will help you meet your customers’
demand for greener solutions.
This edition of the Engineering Journal features four articles written for engineers facing the energy challenges of today.
I hope that they inspire you with new ways to conserve resources.
Together, we can meet today’s most pressing technical and business challenges and make the world a better place. That’s
“Engineering Success.”
Tunç Doluca
President and Chief Executive Officer
Do you know how much your devices cost to operate?
Find out with Maxim’s energy cost calculator:
www.maxim-ic.com/energy-calc
Innovation Delivered is a trademark and Maxim is a registered trademark of Maxim Integrated Products, Inc. © 2009 Maxim Integrated Products, Inc. All rights reserved.
Reduce Standby
Power Drains
with Ultra-LowCurrent, Isolated,
Pulse-FrequencyModulated (PFM)
DC-DC Converters
consideration, and for safety concerns, galvanic isolation
is an important aspect of the design.
To address these concerns, designers must focus on
the design of the DC-DC converter to ensure that it
consumes as little current as possible during no-load
conditions. All DC-DC converters, even during
standby, can consume significant quiescent current.
One commercial power-supply module (the Recom ®
R-78A3.3-1OR), for example, draws about 7mA under
no-load conditions. However, with some attention to
topology and careful design, an isolated DC-DC converter
module with a no-load current drain of less than 1mA
can be implemented.
The 30X difference in current drain can translate into
reduced battery replacements. For example, even if
the system’s batteries are rechargeable, then additional
recharge cycles might be needed if the higher currentdrain supply is used. Moreover, batteries that are
recharged often, wear out sooner and end up in landfills.
Similarly, if the device employs one-time-use batteries,
they will discharge sooner with a higher standby current
and get discarded more frequently.
Javier Monsalve Kägi, Senior Member of Technical
Staff, Applications, Maxim Integrated Products, Inc.
Jose Miguel de Diego
Escuela Técnica Superior de Ingeniería, Bilbao, Spain
Jose Ignacio Garate
Escuela Técnica Superior de Ingeniería, Bilbao, Spain
While there are several approaches to the challenge, this
article looks at the use of pulse-frequency modulation
(PFM) to achieve a 1700:1 ratio between the device’s on
and standby states.
This article explains how to reduce the level of
low-current consumption in isolated DC-DC power
supplies and how to improve the performance of those
supplies under no-load conditions. Sensitive to today’s
need for innovative “green” solutions, the discussion
especially focuses on ways to extend the battery life of
battery-powered electronic devices and communicationsystem devices with discontinuous transmission.
System Characteristics
Typical power consumption versus time looks like the
graph in Figure 1. Here the load current spikes during
operation or active charging, and then drops when the
device is idle. The idle current, IZ, must be minimized
to reduce the battery drain and extend the battery life
and standby time. Thus, the isolated DC-DC converter
needs ultra-low current consumption when no load is
connected, and should also provide high isolation from
input to output. Ideally, the converter should also offer
high conversion efficiency and a small footprint.
Today, many industrial systems employ battery-powered
sensors and transponders to eliminate expensive cable
installations and to reduce overall system power
consumption. These industrial systems typically have
an active mode and a standby mode. In active mode the
sensor delivers data to the transponder (a radio modem)
which transmits the data to a host system. In standby
mode the transponder and sensor go to sleep for a fixed or
variable time period. This start-and-stop operation, often
referred to as a discontinuous operating mode, maximizes
the battery life of the device.
Q1 = t1 ✕ l1
ILOAD
For an application like a watering system that leverages
GSM radio modules for the sensors, maintenance costs
would be high if the batteries powering the GSM radios
had to be replaced every few days, or even every few
weeks. Since such a system spends most of its time
in standby or sleep mode, minimizing the power drain
from the battery when no activity is taking place would
go a long way toward extending battery life. In this
system no-load quiescent current becomes a key design
I1
t1
Q2 = t2 ✕ l2
t2 = kt ✕ t1
I2 / I1 = kI
I2
t
Figure 1. The relationship between the on and standby states of a communication device with discontinuous transmission.
3
Table 1. Characteristics of Commercial DC-DC Converters
Manufacturer
Electronic AG
XP Power
Recom Power International
C&D Technologies®
Bourns® Inc.
Recom Power International
Traco®
Model
TEN 5-1210
JCA0412S03
RW-123.3S
HL02R12S05
MX3A-12SA
R-78A3.3-1
VI (V)
12
12
12
12
12
12
VO (V)
3.3
3.3
3.3
5
3.3
3.3
The typical commercial DC-DC converters listed in
Table 1 show input currents of 7mA to 40mA when no
load is connected with an input of 12V. These converters
traditionally employ pulse-width-modulation (PWM)
controllers. However, PWM controllers always have an
active oscillator, even when there is no load, and that
oscillator continually draws current from the battery.
IO (A)
1.2
1.2
0.7
0.4
3.0
1.0
II (IO = 0, mA)
20
38
21
40
11
7
η (%)
77
83
65
60
93
81
Isolation
✓
✓
✓
✓
The most common approach solves the problem by using
either an auxiliary winding or an optocoupler.
The power-supply topology is a step-down approach;
the battery pack used by the application has a nominal
voltage of 12V, while the internal electronic circuits in
the system operate at 3.6V, nominal. Figure 2 shows the
schematic diagram of the DC-DC switching regulator, and
the Bill of Materials with component values is provided in
Table 2. When the control loop is regulating the voltage,
the optocoupler requires a constant current through the
LED on the primary side of the transformer. The lower
limit of the current is fixed by the optocoupler’s CTR
at low bias currents (63% at 10mA, and 22% at 1mA)
and by a reduction of the response time (2µs at 20mA
and 6.6µs at 5mA).
A PFM Controller Topology
An alternative approach is to use a DC-DC converter that
employs a pulse-frequency-modulation (PFM) controller.1
A PFM controller uses two one-shot circuits that only
work when the load drains current from the DC-DC
converter’s output. The PFM is based on two switching
times (the maximum on-time and the minimum off-time)
and two control loops (a voltage-regulation loop and a
maximum peak-current, off-time loop).
The current consumption of the output voltage-divider
(formed by resistors R5 and R11) is fixed to 7µA.
Because of this, the 0.5µA required by the reference
input plus its thermal deviation does not significantly
affect the output voltage. Additionally, the voltage
measured at the divider output does not suffer a relevant
delay, thanks to the low-input capacitance. This latter
fact precludes the need for a capacitive divider to reduce
the input capacitance of the precision reference. In the
optocoupler, the phototransistor draws 60µA (|IFB| <
60nA), which translates into a current flow through the
LED of less than 230µA (CTR ~26%).
The PFM is also characterized by control pulses of
variable frequency. The two one-shot circuits in the
controller define the TON (maximum on-time) and the
TOFF (minimum off-time). The T ON one-shot circuit
activates the second one-shot, T OFF . Whenever the
comparator of the voltage loop detects that VOUT is out
of regulation, the TON one-shot circuit is activated.
The time of the pulse is fixed up to a maximum value.
This pulse time can be reduced if the maximum peakcurrent loop detects that the current limit is surpassed.
The quiescent current consumption of a PFM controller is
limited only to the current needed to bias its reference and
error comparator (10s of µA). In contrast, the internal
oscillator of a PWM controller must be turned on
continuously, leading to a current consumption of several
milliamps. The implementation presented in this article
keeps the current consumption to less than 1mA at 12V by
using a PFM controller topology.
Controlling It All
To implement a PFM controller, the MAX1771 BiCMOS
step-up, switch-mode power-supply controller (U1) can
be used to provide the necessary timing. The MAX1771
offers improvements over prior pulse-skipping control
solutions: reduced size of the inductors required, due
to a 300kHz switching frequency; the current-limited
PFM control scheme achieves 90% efficiencies over
a wide range of load currents; and a maximum supply
current of just 110μA. Besides these advantages, the
main characteristics of the MAX1771 in a nonisolated
application are: 90% efficiency with load currents
ranging from 30mA to 2A; up to 24W of output power;
and an input-voltage range of 2V to 16.5V.
Field systems such as the watering system must endure
harsh environments, and thus the DC-DC converter
in those systems should be galvanically isolated. A
transformer provides the isolation, but the challenge is
to feed back the voltage reference from the secondary
side to the primary side without breaking the isolation.
4
the following characteristics: 100µF, 6.3V, X5R, and
1206 size (Kemet® C1206C107M9PAC). Using ceramic
capacitors reduces the capacitor leakage to just a few
microamps. Note, however, that the ceramic capacitors
cost about 3x that of the tantalum capacitors, and that
difference would increase the system cost.
The resistances of the voltage-control loop have been
chosen to have the highest possible values. This decision
represents a trade-off between current consumption and
loop stability. As a result, the current through the voltagedivider is less than 7µA. Since the filtering capacitors are
nonideal, capacitor leakage current must be added to this
current. In this design, filter capacitor-leakage current in
C5 and C8 is less than 20µA. If lower leakage is required,
these caps could be upgraded to ceramic capacitors with
Figure 3 shows the prototype PFM DC-DC converter
that draws a quiescent current of just 0.24mA. The
T1
D1
L1
R1
C1
5
C2
U1
V+
REF
4
SHDN
EXT
2
1
U2
R3
M1
R2
C3
R4
C4
6
3
MAX1771
AGND
FB
CS
GND
R6
8
7
C9
R5
C7
R7
D2
R8
C8
U3
R9
C5
C6
R10
R11
C10
Figure 2. Schematic of an isolated PFM flyback DC-DC converter.
Table 2. Component Bill of Materials for PFM Flyback DC-DC Converter
Reference
Values
C2
470µF 25V
C10
180pF
C1, C4, C7
100nF 16V
C5, C8
100µF 16V 0.1Ω
C6
100pF
C3
1nF 50V
C9
150pF
D1
MBRS230LT3G
D2
MBRA160T3G
L1
22µH 1.2A 0.19Ω
M1
IRFR120
R1, R6
R9, R2
R3
R4
R5
R7
R10
R11
R8
T1
U1
U2
680Ω
100kΩ
10Ω
4.7kΩ
390kΩ
0.047Ω
270kΩ
820kΩ
100Ω
EP10 3F3
MAX1771
TLV431A
U3
SFH6106-2
Description
CEL 470µF, 25V, +105°C,
10mm x 10mm SMD
CS 180p C COG, 50V 0603/1
#CSMD 100nF K X7R 16V 0603/1
CEL TAN 100µF ±20% E 16V 0.1Ω
CS 100p C COG 50V 0603/1
#CS 1n M X7R 50V 0603/1
CS 150p C COG 50V 0603/1
D Schottky 2A, 30V SMB
D Schottky 1A, 60V SMA
L SMD 22µH, 1.2A, 0.19Ω
Q IRFR120 DPAK 8.4A, 100V,
0.270Ω, NMOS
RS 680R J 1/16W 0603/1
#RS 100K F 1/16W 0603/1
#RS 10R J 1/16W 0603/1
#RS 4K7 J 1/16W 0603/1
#RS 390K F 1/16W 0603/1
RS R047 J 1206 /1
RS 270K F 0603 /1
RS 820K F 0603 /1
#R SMD 100R -J 1206/1
T SMD EP10 3F3 NUCTOR
DC-DC controller
U TLV431A V.REF 1.25V SOT23-5
#U SFH6106-2 OPTO 63-125%,
5.3kV SMD-4
5
Manufacturer
UUD1E471MNL1GS (Nichicon®)
GRM39 COG 181 J 50 PT (Murata®)
GRM39X7R104K16PT (Murata)
T495D107K016ATE100 (Kemet®)
GRM39 COG 101 J 50 PT (Murata)
GRM39 COG 271 J 50 PT (Murata)
GRM39 COG 151 J 50 PT (Mutata)
MBRS230LT3G (ON Semiconductor(s))
MBRA160T3G (ON Semiconductor)
SRR0604-220ML (Bourns®)
IRFR120 (Int.Rectifier.)
RK73B 1J T TD 680 J (KOA Speer®)
RK73H 1J T TD 1003 F (KOA Speer)
RK73B 1J T TD 100 J (KOA Speer)
RK73H 1J T TD 4701 J (KOA Speer)
RK73H 1J T TD 3903 F (KOA Speer)
SR73 2B T TD R047 J (KOA Speer)
RK73H 1J T TD 2703 F (KOA Speer)
RK73H 1J T TD 8203 F (KOA Speer)
RK73B 2B T TD 101 J (KOA Speer)
CSHS-EP10-1S-8P-T (Ferroxcube®-Nuctor)
Maxim Integrated Products
TLV431ACDBVR (Texas Instruments™)
SFH6106-2 (Vishay®)
Table 4. Efficiency at Nominal Voltage for Different
Loads
VIN (V) IIN (mA) VOUT (V) IOUT (A) Efficiency (%)
12.0
0.24
3.615
0
0
12.0
61
3.615
0.14
69.14
12.0
83
3.615
0.2
72.59
12.0
121
3.615
0.3
74.69
12.0
160
3.615
0.4
75.31
12.0
200
3.615
0.5
75.31
12.0
240
3.615
0.6
75.31
12.0
281
3.615
0.7
75.04
12.0
323
3.615
0.8
74.61
12.0
367
3.615
0.9
73.88
12.0
411
3.615
1.0
73.30
Figure 3. Top view of the DC-DC PFM converter prototype for
wireless applications.
Table 3. Current Consumption Under a No-Load State
for Different Input Voltages
VIN (V)
10.0
12.0
15.0
IIN (mA)
0.244
0.239
0.227
VOUT (V)
3.615
3.615
3.615
IOUT (A)
0
0
0
loop may oscillate during certain load conditions. To
prevent self-oscillation, designers must account for the
various tolerances of the components in a production
environment. Thus, the values of the resistors and
capacitors used in the loop must be selected with care.
board measures less than 50mm by 30mm, can deliver
3.6W with an input-voltage range of 10V to 15V (12V
nominal), and operates at a switching frequency of
300kHz. The converter can supply a maximum constant
output current of 1A while delivering a regulated output
of 3.6V. Employing a flyback topology (step down) with
both current and voltage feedback control, the converter
output is galvanically isolated from the input.
Table 4 provides the values for the input and output
parameters of the power supply at various load conditions.
The optimum efficiency is reached at normal conditions
and within the nominal load range.
The efficiency of the DC-DC converter with no load
is represented as zero (Figure 4), because the current
consumed by the wireless device in standby mode and
referred to the 3.6V output side is below 140µA. This
current is negligible, when compared to the 0.24mA of
the power supply’s input-current consumption under
no-load conditions.
The prototype can be used in various wireless applications
that operate in a discontinuous transmission mode. The
current consumption of the modules can peak at 3A, and
the maximum mean current is 1A. To reduce the current
peaks and avoid the problems that they generate in the
performance of the radio, the techniques described in
references 2 and 3 are used. Additionally, some basic
guidelines suggest that designers should use high-value
capacitors that have low series resistances.
The waveforms in Figures 5a, b, c, and d show the
output voltage and control voltage for various loads; the
control pulses at the gate of the switching device become
more frequent as the load increases. The converter
prototype shows the signals at no load, 100mA, 500mA,
and 1A current loads. The scope traces graphically
illustrate the operation of the PFM control scheme. The
lower scope trace is scaled by 5x to make it more visible.
The X axis represents the time and the Y axis the voltage.
Qualifying Design Performance
To verify the performance of the power supply, the
following parameters are measured: the input voltage,
VI; the input current, II; the nominal output voltage, VO;
the load current consumption, IO; and the efficiency of
the power supply. Tables 3 and 4 show the measurement
results, including the losses on the common-mode input
filter and the losses of the protection circuitry. It is also
important to remember that power supplies handling
low power levels are not as efficient as power supplies
handling higher loads. The higher-load power supplies
are usually synchronous, which helps to reduce the losses
in the active devices.
Summary
Initial industry surveys indicate that the best commercial
isolated DC-DC converters for power supplies with low
current consumption under no-load conditions typically
have about 20mA minimum current consumption. With
minimal effort, however, designers can use a PFM
scheme to implement a low-IQ, isolated power supply
that has the lowest current consumption on the market.
The no-load current consumption of the power supply
presented here is only 0.24mA.
The current consumption of the power supply with a
PFM control scheme has been reduced to 0.24mA. Due
to component values selected, however, the control
6
80
EFFICIENCY (%)
60
40
20
0
0
0.2
0.4
0.6
0.8
Figure 5d.Output voltage and control voltage for 1A load
(20ms/div, CH1 1V/div, and CH2 5V/div).
1.0
OUTPUT CURRENT CONSUMPTION (A)
References
1Maxim Integrated Products application note 664, “Feedback Isolation
Augments Power-Supply Safety and Performance,” www.maxim-ic.com/an664
and EDN magazine (June 19, 1997).
2J. Ig. Garate, J. M. de Diego, “Consequences of Discontinuous Current
Consumption on Battery Powered Wireless Terminals,” [ISIE06, Paris, France,
Oct. 2006].
3J. M. de Diego, J. Ig. Garate, “Improvements of Power Supply Systems in
Machine to Machine Modules and Fixed Cellular Terminals with Discontinuous
Current Consumption,” [Digests 9th ICIT06, Mumbai, India, Dec. 2006].
Figure 4. Efficiency of the power supply for different load conditions
at the input nominal voltage (12V).
Additional Reading
1. I. Haroun, I. Lambadiris, R. Hafez, “RF System Issues in Wireless Sensor
Networks,” Microwave Engineering Europe (Nov. 2005), pp. 31–35.
2. J. P. Joosrting, “Power dissipation could limit smartphone performance,”
Microwave Engineering Europe (Apr. 2006), comment p. 9. Available at:
www.mwee.com.
3. “MAX1649/MAX1651, 5V/3.3V or Adjustable, High-Efficiency,
Low-Dropout, Step-Down DC-DC Controllers,” Maxim Integrated Products
Data Sheet, 19-0305; Rev 2; 9/95.
4. “MAX1771, 12V or Adjustable, High-Efficiency, Low IQ, Step-Up DC-DC
Controller,” Maxim Integrated Products Data Sheet, 19-0263; Rev 2; 3/02.
5. J. Ig. Garate, J. M. de Diego, J. Monsalve, “Ultra Low Input Current
Consumption Power Supplies,” [ISIE07, Vigo, Spain, Jun. 2006].
6. J. Ig. Garate, J. M. de Diego, J. Monsalve, “Sistemas de transmisión
discontinua. FAC aisladas y de muy bajo consumo en vacío,” Mundo
Electrónico (Oct. 2007), pp. 38–45.
7. R. W. Erikson, Fundamentals of Power Electronics, 1st Ed. (Chapman and
Hall, New York, 1997).
8. B. Arbetter, R. Erikson, and D. Maksimovic, “DC-DC converter design for
battery-operated systems”, Proceeding of IEEE Power Electronic Specialist
Conference, (1995), pp. 102–109.
9. B. Sahu and G.A. Rincora, “A Low Voltage, Non-Inverting, Dynamic,
Synchronous Buck-Boost Converter for Portable Applications,” IEEE
Transactions on Power Electronics, vol. 19, no. 2, (Feb. 2004), pp.443–452.
10. G.A. Rincora and P.E. Allen, “A Low-Voltage, Low Quiescent Current, Low Drop-Out Regulator,” IEEE Journal of Solid-State
Circuits, vol. 33, no. 1, (Jan. 1998), pp. 36–44.
11. D. Maksimovic, “Power management model and implementation of power
management ICs for next generation wireless applications,” Tutorial Presented
at the International Conference on Circuits and Systems (ISCAS), (2002).
12. Data Acquisition Linear Devices Databook. Vol. 3, National Semiconductor
Corporation (1989).
13. “TPS62110 TPS62111 TPS62112, 17-V, 1.5-A, Synchronous Step-Down
Converter,” Texas Instruments Incorporated, SLVS585–JULY 2005 (2006).
Figure 5a.Output voltage and control voltage without load
(10ms/div, CH1 1V/div, and CH 2 5V/div).
Figure 5b.Output voltage and control voltage for 0.1A load
(20ms/div, CH1 1V/div, and CH2 5V/div).
C&D Technologies is a registered trademark of C&D Charter Holdings, Inc.
Bourns is a registered trademark of Bourns Inc.
Ferroxcube is a registered trademark of Ferroxcube International Holding B.V.
Kemet is a registered trademark of KRC Trade Corporation.
KOA Speer is a registered trademark of KAO Speer Electronics, Inc.
Murata is a registered trademark of Murata Manufacturing Co., Ltd.
Nichicon is a registered trademark of Nichicon Corporation.
ON Semiconductor is a registered service mark of Semiconductor Components
Industries, L.L.C.
Recom is a registered trademark of Recom International Power.
Texas Instruments is a trademark of Texas Instruments Incorporated.
TRACO is a registered trademark of Traco Electronic AG.
Vishay is a registered trademark of Vishay Intertechnology, Inc.
Figure 5c.Output voltage and control voltage for 0.5A load
(20ms/div, CH1 1V/div, and CH2 5V/div).
7
Keep Power
Consumption
in Check with
Low-Power
Comparators
that Autosense
Plugged-In
Accessories
VCC
1kΩ
AUDIO LEFT
DETECT TO BUFFER
AUDIO RIGHT
1OOkΩ
Figure 1. An automatic jack-detection circuit.
generates a signal to indicate the presence of a headphone
or other external device. In a typical connection, the detect
pin is disconnected if an external device in inserted.
The output signal is pulled high when no jack is present
and pulled low when the jack is inserted. This detect
signal is routed to a microcontroller port, which can
then autoswitch the audio signal between a loudspeaker
(headphone absent) and the headphone speakers
(headphone present).
Arpit Mehta, Strategic Applications Engineer
Portable electronic devices usually include a single 3- or
4-connector jack which can be a stereo headphone jack,
a mono headphone jack with microphone input and hook
switch, or a stereo headphone jack with microphone/
hook-switch combination. Tiny, ultra-low-power
comparators like the MAX9060 series can be configured
in various ways not only to consume negligible power,
but also to provide small, simple, and cost-effective
detection of external accessories.
A simple transistor can buffer the detect signal before
it reaches the microcontroller input. The transistor also
provides any level translation necessary for interfacing
with the controller. In space-constrained applications like
cell phones and PDAs, a small transistor packaged no
larger than a couple of millimeters is preferred. Buffering
and level translation can also be implemented with
low-cost, low-power comparators in ultra-small packages.
Members of the MAX9060 family, for example, come in
1mm × 1mm chip-scale packages and consume just 1µA
of current.
A common feature in most of the electronic devices
used today (cell phones, PDAs, notebooks, handheld
media players, game systems, etc.) is the provision for
connecting external accessories. The devices, therefore,
include dedicated logic circuitry not merely to detect the
presence of an accessory, but to identify its type so the
internal control circuitry can adjust accordingly.
Headset Detection
The audio socket in Figure 1 is designed to handle the
popular three-conductor audio plug. This plug connects
either to a stereo headphone or a mono headset with
microphone. You can easily differentiate between the
stereo and mono-plus-microphone headset by using the
circuits discussed below. These circuits leverage the
fact that headphone resistance is low (usually 8Ω, 16Ω,
or 32Ω) and that microphone resistance is high (600Ω
to 10kΩ).
Adding circuits to implement the autodetection/selection
function can increase a system’s power budget, and that
is a problem. As designers, we need to minimize the power
budget to ensure that the systems deliver the “greenest”
possible solution with the smallest footprint. To that end,
tiny, ultra-low-power comparators such as the MAX9060
series offer the best solution in the semiconductor market.
These comparators are key to helping designers stay within
their power-consumption budget.
A brief introduction to the common audio jack and the
electret microphone is helpful in understanding these
circuits. In a three-conductor audio jack (Figure 2), the
“tip” carries the left-channel audio for a stereo headphone
or the microphone connection for a mono headset with
microphone. For stereo headphones, “ring” connects to
Hardwiring Detects the Presence of a Jack
We begin with a quick review of the basics of automatic
jack detection.
Consider a typical headphone-socket circuit (Figure 1).
Connecting a pullup resistor to the detect pin, as shown here,
8
INSULATION
RING
VCC
RBIAS
TIP
OUTPUT
SLEEVE
Figure 2. A three-conductor audio jack.
the right channel and “sleeve” to ground. For a mono
headset with microphone, ring connects to the input audio
channel for the mono microphone and sleeve connects
to ground.
Figure 3. An electrical model of an electret microphone.
Electret Microphones
producing the voltage V DETECT at the noninverting
input of the MAX9063. This resistance can be small
for stereo headphones (8Ω, 16Ω, or 32Ω), or high due
to the microphone’s constant-current sink which ranges
from 100µA to about 800µA according to the type of
microphone. Because VDETECT varies with the model
of headset plugged in, the headset type is detected by
monitoring VDETECT with a comparator.
A typical electret microphone (Figure 3) has a
condenser element whose capacitance varies in response
to mechanical vibrations, thereby providing voltage
variations proportional to the sound waves. Electret
microphones have a permanent, built-in static charge
and, therefore, require no external power source. They
do, however, require a few volts to power an internal
preamplifier FET.
Assuming that the microcontroller’s reference voltage
(V MIC-REF ) is 3V as shown, a 32Ω headphone load
produces 43mV at V DETECT . A constant 500µA
microphone load, however, produces 1.9V. Note that a
direct interface for VDETECT can be challenging in most
practical cases. Assuming that the CMOS inputs of a
typical microcontroller port demand logic levels above
0.7 × VCC and below 0.3 × VCC, then the input logic for a
controller operating with a 3.3V supply should be above
2.3V and below 1V.
The electret microphone appears as a constant-current
sink that provides very high output impedance. Its high
impedance is then converted by the FET preamplifier
to the low impedance necessary for interfacing with the
subsequent amplifier. Thus, the electret microphone’s
low cost, small size, and good sensitivity make it a
good choice for applications like hands-free cell-phone
headsets and computer sound cards.
The microphone is biased through a resistor (usually
1kΩ to 10kΩ) and a supply voltage that provides the
necessary constant-bias current. This bias current ranges
from 100µA to about 800µA, depending on the particular
microphone and its manufacturer. The bias resistor is
selected according to the applied supply voltage, the
desired bias current, and the required sensitivity. Based
on these factors, the necessary bias voltage varies from
part to part and with operating conditions. A 2.2kΩ load
resistor with 3V supply drawing 100µA, for example,
develops a bias voltage of 2.78V. A similar resistor
drawing 800µA under similar conditions develops a bias
voltage of 1.24V.
A 1.9V level generated by a 500µA microphone load does
not qualify as a valid logic 1. Microphone bias currents
from 100µA to 800µA generate VDETECT levels from
2.78V to 1.24V, and any voltage below 2.3V violates the
controller’s VIH specification (input high level, assuming
2.2kΩ for RBIAS). To get 2.3V or above, the microphone
bias current must be 318µA or less. Otherwise you
must change the 2.2kΩ bias-resistor value which, in
turn, changes the sensitivity point of the microphone.
Generating a logic low of 1V and below is easy, because
headphones with typical 32Ω loads can easily pull the
level close to ground.
To detect the type of headset connected, you therefore
feed V DETECT to one input of a comparator and a
reference voltage to the other input. The comparator’s
output state then represents the type of headset.
To detect the type of headset connected, refer to
Figure 4. Here a 2.2kΩ R MIC-BIAS resistor connects
to a low-noise reference voltage from the audio
controller (VMIC-REF). When an audio jack is inserted,
this V MIC-REF voltage is applied through R MIC-BIAS
to the tip-to-ground resistance (not shown), thus
The comparator for this portable headset-detect
application should be tiny and consume little power. The
9
VDETECT
43mV FOR 32Ω
1.9V FOR 500µA MIC BIAS
3.3V
3V
RMIC-BIAS
2.2kΩ
MIC-IN
VMIC-REF
VCC
AUDIO LEFT
DETECT
PORT 1
AUDIO
CONTROLLER
AUDIO RIGHT
VCC
100kΩ
µC
OUT
0.2V
REF
PORT 2
++
MAX9063
1 = HEADPHONE
0 = MICROPHONE
Figure 4. A comparator circuit used for headset detection.
comparator in Figure 4 is just 1mm × 1mm and draws a
maximum supply current of only 1µA. Its strong immunity
to cell-phone frequencies provides highly reliable
operation. The comparator also has internal hysteresis
and low-input bias currents. These features make it an
excellent choice for headset detection in battery-operated,
space- and power-sensitive applications like cell phones,
portable media players, and notebook computers.
The voltage VDETECT (Figure 5) is pulled close to ground
when the hook switch is pressed, and interpreted as
logic 0 by the microcontroller. When the hook switch is
open, however, VDETECT may violate the VIH spec for
the CMOS inputs. Those V DETECT inputs can vary
between 1.24V and 2.78V, depending on the value of
RMIC-BIAS (2.2kΩ in this case) and the type of microphone
in the headset.
Thus, a direct interface between the hook switch and
the controller is not possible for all microphone types.
Instead, a low-power comparator can be used as in Figure
5. Here the reference level is set to detect a given type of
microphone, while also indicating the status of the hook
switch. The comparator output is pulled high when the
hook switch is pressed, and pulled low when the switch
is open. Again, the MAX9060 series of comparators
provides a low-power solution for these hook-switchdetect applications.
Hook-Switch Detection
Most hands-free headsets include a switch, usually known
as a hook switch, that accepts and ends calls; provides
the MUTE/HOLD function; and holds an ongoing call
while receiving a second call. The microcontroller
controlling the headset needs to detect the status of the hook
switch and the presence of the headset. The jack (hence
the headset) can be detected automatically (Figure 1). A
signal for the hook-switch status can also be generated.
The scope shot of Figure 6 is triggered by pressing the
hook switch of a mono headset. The setup is identical to
that of Figure 5, but a 2.5mm universal headset for cell
phones is used for the test. The headset tip has an electret
microphone with hook switch and 32Ω speaker connected
to its ring. That microphone draws a constant bias current
of 212µA when powered with a 3V supply through the
2.2kΩ bias resistor.
Status-detection circuitry for the hook switch comprises a
4-connecter stereo headset with microphone and a parallel
hook switch (Figure 5). (A mono headset is similar,
but has a 3-pin connector.) In both headset types the
tip is connected to the microphone in parallel with the
hook switch. As shown, the hook switch presents a low
resistance when pressed, and a high microphone resistance
when open. As with the headset detection explained above,
an interface between the headphone-detection voltage and
the CMOS inputs of the microcontroller can complicate
the circuit design for microphone/hook-switch detection.
The DC voltage observed at V DETECT is 2.52V
(Figure 6), which causes the MAX9063’s output to
assert low. Pressing the hook switch grounds VDETECT,
allowing the output to be pulled high by an external
10
3.3V
3V
RMIC-BIAS
2.kΩ
VMIC-REF
VCC
MIC-IN
AUDIO LEFT
AUDIO
CONTROLLER
AUDIO RIGHT
L
VMIC-REF
1.9V FOR 500µA
MIC LOAD
R
MIC
HANDS FREE
HOOK
SWITCH
VCC
µC
0.2V
REF
PORT 2
GND
++
MAX9063
Figure 5. Hook-switch detection circuitry using the MAX9063 comparator.
Summary
10kΩ pullup resistor. Thus, the MAX9063 comparator
in its tiny 1mm × 1mm CSP package is well suited for
detecting hook switches and accessories. The MAX9028
comparator family is also suitable for these applications.
There is a common need for detecting jacks, headsets,
and hook switches in portable applications. Dedicated
comparators such as the MAX9063 and MAX9028 series
devices are ideal for those applications, especially as
they occupy very little real estate and consume negligible
power. These comparators offer an economical solution
for detection circuitry in portable applications.
Figure 6. These waveforms are taken from an electret microphone with hook switch, controlled by a mono headset and its internal control circuitry. When the hook switch of a mono headphone is pressed, the comparator detects the shorted microphone, thereby allowing its output to be pulled to a logic high.
11
Low-Loss LED
Driver Improves a
System’s Green
Footprint by
Boosting Efficiency
and Extending
Battery Life
LINEAR REGULATOR
HOT
MONITOR
CONTROLLER
1 OR
MULTIPLE
LEDs
Figure 1a. A simple linear regulation scheme experiences power losses
due to both the regulator and the current-setting resistor.
The advantages of this circuit are its simplicity and the fact
that it generates no EMI. The circuit can, however, only
lower voltage and it does generate some heat.
Keith Welsh, Senior Member of the Technical Staff
Providing power to drive high-brightness LEDs (HB
LEDs) can be achieved by a number of different
schemes. Because many systems are battery powered,
energy efficiency is key to maximizing each battery
charge and the system’s operating time. By improving
battery efficiency you also improve the system’s “green”
footprint. Over the life of the battery for the same number
of charge cycles, longer times between charges translate
into potentially hundreds of hours of additional use from
the batteries. Thus fewer batteries may end up in landfills
or hazardous waste-disposal sites.
SWITCHING REGULATOR
HOT
MONITOR
CONTROLLER
1 OR
MULTIPLE
LEDs
The usual approach for low-power lighting is a simple
linear regulator configured to operate in a constant-current
mode (Figure 1a). This linear regulator offers the benefit
of simple design. Its main disadvantage, however, is its
high power loss, since the surplus headroom voltage is
dissipated as heat in the current-measuring resistor and
the regulator itself. This heat could also have a negative
effect on the system’s “green” footprint. More heat might
require more cooling (a fan or large metal heatsink) which
could consume still more energy, space, and weight while
adding to materials cost and manufacturing time.
Figure 1b. In a basic switch-mode-regulation approach the main
source of power loss comes from the energy dissipated by
the current-sensing resistor. This design is highly efficient
and can be reconfigured to boost voltages. It is, however,
a more complex circuit and can generate EMI.
To reduce the power loss due to the current in the resistor,
a low-loss current-measuring scheme such as a resistor/
amplifier combination can be incorporated to provide the
required feedback voltage to the switching converter. One
such approach employs a dedicated, precision currentsense amplifier such as the MAX9938H, which generates
100V/V sensed across the series current-measuring
resistor. This approach reduces the losses in the feedback
portion of the circuit to only a few milliwatts. The
low-value sense resistor required can even be derived
from a short length of copper trace on the board at zero
cost, making this an attractive solution.
An alternative method employs a switch-mode-regulation
scheme such as a buck regulator (Figure 1b). This type
of regulator often requires a feedback voltage between
0.8V and 1.3V to regulate the current to the LED. The
current-measurement scheme to set that voltage typically
employs a low-value resistor in series with the LED.
The voltage developed across this resistor provides the
feedback voltage that maintains the constant-current
power supply to the LED. The losses in the regulator can
thus be reduced, but there are still losses in the system due
to the power dissipated by the current-measuring resistor.
In the circuit shown in Figure 2, the boost converter
configuration features the MAX9938H current-sense
12
INPUT VOLTAGE
1.2V TO 5.5V
12.65mΩ RESISTOR
EQUIVALENT TO
~2.6cm OF 1mm WIDE
36µm COPPER TRACE
BATT
For this application, the MAX8815A would be used in
the higher power fixed-PWM mode and the shutdown pin
would either enable or shut down the drive. In shutdown
mode, the MAX8815A consumes only 100nA of current
from the battery, thus prolonging the battery’s operational
life and the time required between recharges.
LX
1A
ON
POUT
MAX8815A OUTS
Along with the MAX8815A converter, the MAX9938H
current-sense amplifier controls the current, thereby
keeping a constant 1A flowing into the LED. This
amplifier integrates the gain-setting resistors on its inputs
for a gain of 100V/V. Additionally, it offers precision
accuracy specifications with a VOS of less than 500µV
(max) and a gain error of less than ±0.5% (max). The
MAX9938H consumes just 1µA in its quiescent state.
Other values of current can be achieved with a different
value shunt resistor (possibly derived from a copper
trace), perhaps modified or trimmed with a chip resistor
in parallel.
PB
SKIPB
GND
RS+
RS-
R1
R1
10kΩ
MAX9938H
P
ROUT
This design approach presents a five-component solution,
and the battery’s operational life is maximized since the
power losses are minimized in both the regulator and
the control loop. Samples and evaluation kits for the
MAX8815A and MAX9938H are available now.
GND
Figure 2. Working from Figure 1b, a current-sense amplifier such as
the MAX9938H reduces power losses in the current-sensing
resistor to just a few milliwatts vs. hundreds of milliwatts,
or more, for the previous schemes in Figure 1.
amplifier and uses a MAX8815A step-up converter to
get its power from two NiMH series-connected cells.
The MAX8815A operates at switching frequencies
up to 2MHz with efficiencies up to 97%. That highswitching frequency minimizes the size of external
components; internal compensation further reduces the
external component count for cost- and space-sensitive
applications. The converter can generate any output
voltage from 3.3V to 5V from a two-cell NiMH or NiCd
source or a single-cell Li+/Li polymer battery.
The MAX8815A has two operating modes: a low-power
mode and a fixed-frequency, forced-PWM mode for
heavy loads. Low-power mode consumes only 30µA
of quiescent current and allows the converter to switch
only when needed at no load and light loads. Low-power
mode delivers the best efficiency for light loads and helps
minimize wasted power and drain on the battery.
The second mode handles heavier loads (typically
above 90mA) and uses a fixed-frequency forced-PWM
scheme in which the converter switches at a fixed
frequency irrespective of the load. This mode allows easy
noise filtering and lower output ripple, but consumes
more power.
13
Little Things Mean
a Lot
while typical goals for operating efficiencies of more than
80% are becoming commonplace.
As a consumer, reading our home utility power bill can be
frightening. As an engineer, we can design circuits to help
consumers reduce their power bills. For example, just
look at the HDTV DVR receiver. A typical unit draws
120W and often has no standby mode. Running 24/7, it
would cost $34.52 (US dollars) a month to operate (based
on the penalty power rate of $0.399 per kWh in northern
California). This is just one appliance in our home, which
emphasizes how the costs or potential savings can add
up quickly. In a typical middle-class home there might
be over 35 devices drawing power. Most, thankfully,
probably have some form of standby power mode that
reduces the power drain when the system is idle.
Bill Laumeister, Principal Member of Technical Staff
Consumers demand long battery life in their portable
devices. Meanwhile for nonportable devices, increasing
energy costs and the latest Energy Star® guidelines are
focusing public awareness on wasted standby power. Thus,
meeting green energy regulations and reducing standby
power has become designers’ new mantra, especially when
systems are active 24 hours a day. To meet the lower powerconsumption levels, circuit designers know that the devil is
in the details, with every single circuit required to justify its
current budget. This article shows how Maxim chips can
help system designers reduce the power budget of typical
systems. The examples highlight just a few of the products
in Maxim’s broad portfolio of ultra-low-current devices.
Increasing energy costs are focusing consumer attention
on the total cost of ownership. Power consumption is
critical, and remember that, for every watt going into a
room, it will cost about two watts for air conditioning to
remove it. So for us engineers, exceeding green energy
regulations is smart for our business and our planet.
Consumers demand long battery life in their portable
devices, and rightfully so. Convenience is paramount,
and that very concept permeates our society. We do not
want to wait in lines, in traffic jams, etc., and further,
we will often pay for that privilege. Hence, we have
automatic teller machines dispensing cash 24/7; digital
video recorders (DVRs) that allow us to time-shift our
entertainment; mobile devices that let us communicate
and entertain ourselves 24/7; and much more. “Little,
light, fast, and easy” is today’s consumer mantra. As
equipment designers, we understand that our success
requires meeting those expectations.
An Elementary Working Machine
Today, we have motors and microprocessors working
for us in our homes and workplaces. When a natural
disaster occurs, we quickly remember how dependant
our lifestyles are on electrical power.
As we look at the block diagrams of machines, appliances,
and entertainment devices, we see much in common.
Figure 1 illustrates the simplest definition of a useful
machine. We, or a machine, sense something and then
initiate an action. This is really a definition of most
work. For example, we sense the room temperature and
turn on a heater or air-conditioning unit. We sense the
light level and turn on the lights. Our lawn sprinkler
controller senses time and turns on the water solenoid for
a programmed period.
Making the equipment “greener” is a combination of
integration, architecture, component selection, and
function management to save every microamp in portable
systems, and milliamps and more in line-powered systems.
In portable systems, designers routinely count current
in microamps. However, even that can be compromised
when a single fingerprint on the circuit board might leak
more current than a chip’s standby current.
MONITOR
POSITION
BRIGHTNESS
VOLUME
METERS
WEIGHT
POSITION
PRESSURE
HUMIDITY
TEMPERATURE
SPEED
A popular song of the last five decades, “Little things
mean a lot,” teaches us how to design circuits for today’s
portable market. To paraphrase the song, with apologies
to the song writers, “cause honestly, honey, they just
cost” battery. We first think of the big items—a sleeping
microprocessor, current-sipping displays, and flash
memories—and then the rest of the circuitry. The devil
is in the details, with every supporting circuit required to
justify its current budget. Regulations vary by area, but
typical goals for standby power are less than 0.5W to 3W,
SENSE
MACHINES
ARE OUR
LIFESTYLE
ACTION
CONTROL
WEIGHT
DIMENSIONS
INTENSITY
VOLTAGE
CURRENT
TIME
MOTORS
VALVES
LIGHTS
SWITCHES
SOLENOIDS
Figure 1. The shared characteristics of common machines dictate our lifestyles.
14
There are several possible amplifier configurations:
We start with the simplest of useful machines and then
add features. Figure 2 is such a machine; it senses some
parameter, uses a processor to evaluate the stimulus
against a predetermined criterion, and starts an output
action. (Yes, we could show a heater, air conditioner, or
refrigerator with a bimetal mechanical switch, but we
are building on this machine to make more sophisticated
devices.) In fact, we are describing a programmable logic
controller (PLC). In Figure 3 we start customizing the
system to meet the customer’s requirement.
SENSE
THE ROOT MACHINE
The input amplifier stage may consist of a MAX9915
op amp and the MAX5490/MAX5492 precisionmatched resistor-dividers, which are matched
to within 0.025%. This combination leverages a
relatively modest op amp, yet delivers precise gain
and an excellent temperature coefficient.
We could add three op amps and a MAX5426
digitally-programmable resistor network to make a
differential-input instrumentation amplifier.
If a programmable-gain amplifier with digitallyprogrammable precision gains of 1, 2, 4, and 8 is
needed, then we combine the MAX5430 precision
voltage-divider with an op amp.
ACTION
VOLTAGE
REFERENCE
INPUT
OP
AMP
PRECISION GAIN
AND SWITCHING
ADC
µC
CALIBRATION
DIGITAL POT
Alternatively, the gain, bias, and offset could be set
with digital potentiometers such as the MAX5128.
The MAX5128 even integrates a nonvolatile memory
so you can set and retain any gain setting. Upon
power-up, the pot assumes the previous value—a
potent tool for calibrating levels and offsets.
OUTPUT
OP
AMP
DAC
BIAS
GAIN
Figure 2. The concept of a simple useful machine is the basis for a PLC whose function is defined through a combination of software and silicon.
To arrive at the system in Figure 3, we took the sensor
inputs and action outputs and partitioned functions by
the speed needed. Relatively slow-changing inputs and
outputs can be multiplexed around one PLC engine.
Multiple parallel PLCs may be required for sensors and
VOLTAGE
actions, such as safety items, which require REFERENCE
constant
attention. Table 1 lists possible components for this root
Op
PLC engine. We can multiplex theINPUT
sensors
and condition
µC
DAC
Amp
the signals by switching gain and offset in the initial op
GAIN
amp. In any large-volume consumer PRECISION
device
this amplifier
& SWITCHING
must be inexpensive. A low-power CMOS op amp such
as the MAX9915 can deliver the necessary precision for
the control loop. The system dictates which of several
amplifier configurations will be used.
The ADC on the control loop is a MAX1108 or MAX1109.
These devices are 8-bit, dual-channel, 50ksps converters
with an internal reference. Table 1 also shows a low-powerconsumption MAX6029 external voltage reference that
can be added if the converters require the higher precision.
The DS80C320/DS80C323 are fast 8051-compatible
microcontrollers. These high-integration controllers
include four 8-bit I/O ports, two full-duplex hardware
serial ports, timer/counters, a watchdog timer, and scratchpad RAM.
OUTPUTallowing more sleep cycles, their highOp By
DAC
Amp
speed architecture
uses less power for equivalent work.
BIAS of the microprocessor is converted to an
The output
GAIN
analog signal by the MAX5380/MAX5381/MAX5382,
8-bit DACs uses a two-wire serial interface to squeeze
the circuit into a space-saving 5-pin SOT23 package. The
DACs also integrate an output buffer amplifier to further
reduce component count and board space.
CALIBRATION
DIGITAL POT
MONITOR
POSITION
PRESSURE
HUMIDITY
TEMPERATURE
SPEED
SENSE
WEIGHT
DIMENSIONS
INTENSITY
VOLTAGE
CURRENT
TIME
POSITION
BRIGHTNESS
VOLUME
METERS
WEIGHT
ROOT
PLC ENGINE
M
U
X
OP
AMP
ADC
µC
DAC
ACTION
CONTROL
PRECISION GAIN
AND SWITCHING
MOTORS
VALVES
LIGHTS
SWITCHES
SOLENOIDS
Figure 3. Highly integrated building-block ICs like those from Maxim can implement an elementary PLC.
15
Table 1. Typical Low-Current Maxim ICs Used for the Root PLC
Part
Description
Current Consumption
MAX1108/MAX1109
8-bit ADC, dual-channel, 50ksps
Operates on < 130µA; standby < 0.5µA
MAX6029
Series voltage reference, 0.15% initial accuracy
Operates on 5.25µA (max)
MAX5380/MAX5381/
MAX5382
8-bit DAC, 2-wire serial interface, 5-pin
SOT23 package
Operates on 230µA; standby 1µA
MAX9915
Op amp, 1MHz unity-gain BW, rail to rail
Operates on 20µA; standby 0.001μA
MAX5490/MAX5491/
MAX5492
Precision-matched resistor-divider, 0.025%
tolerance
Digitally-programmable resistor network for
instrumentation amps
Digitally-programmable precision voltagedivider for programmable-gain amps
MAX5426
MAX5430
Operates on ZERO A; standby ZERO A
Operates on 90µA
Operates on 6µA
MAX308, MAX4581
8-to-1 multiplexer
Operates on < 17µA
MAX5128
Digital potentiometer, nonvolatile
Standby 0.5µA
DS80C320/DS80C323
Microcontrollers, 80C31/80C32 compatible,
fast for power saving
Stop mode: 50µA with bandgap on, 1µA
with bandgap off
Growing the Root PLC for More Complex Devices
By detailing the most elementary PLC engine, it is clear
how features can be added to match the application.
Everyone wants more convenience, which usually means
more features/specialized functions. This is the “feature
creep” that circuit designers hate. Sales wants many
features included, but the retail price cannot increase.
Designers thus must be clever enough to keep costs in
check. Many of Maxim’s highly integrated solutions help
designers meet their application goals by reducing current
consumption, size, and cost.
We are all obligated to conserve energy, and Maxim
takes that obligation seriously. The Company uses
its R&D expertise to design and support a broad line
of power-conserving and energy-efficient products.
Only a few Maxim devices were highlighted in
this article. These devices are just part of Maxim’s
broad portfolio of ultra-low-current products. More
energy saving devices including battery management,
charging, and high-efficiency power supplies are
listed at www.maxim-ic.com.
Energy Star is a registered trademark of the U.S. Environmental Protection Agency.
www.maxim-ic.com
Maxim Integrated Products, Inc.
120 San Gabriel Drive
Sunnyvale, CA 94086
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