Recognized as “the father of the PWM controller IC
industry,” Bob Mammano developed the integrated
circuit that ushered in the age of switching regulators
and switch-mode power supplies. His seminal IC design,
the SG1524, and the many variations it inspired, tamed
tthe complexity of SMPSs, shrinking their size and
making them cost-effective in countless applications.
Mammano also helped shape the analog and power IC
businesses as cofounder of Silicon General and the power IC division of Unitrode, and more recently in his role
as staff technologist at Texas Instruments. Meanwhile,
Mammano has shared his knowledge with engineers
worldwide, leading company-sponsored power supply
design seminars for more than two decades.
Lifetime Achievement Award Recipient
Robert Mammano
By David Morrison, Editor, Power Electronics Technology
I
all of the blocks for a switching power supply together on one
chip. The main reason we did it was that we had a customer
that was interested.”
That customer was Teletype Corp. of Skokie, Ill. Teletype
was in the process of converting its big mechanical teletype
machines into electronic versions. The new teletype designs
didn’t have much space for a power supply, so they needed
a switching power supply. But even then, they didn’t have
room for all of the discrete components required in the complicated control circuitry of a switcher. Although Teletype
had tried to build a switcher using a hybrid product, that
approach was very expensive. “They were convinced that if
someone could do it all for them in a single silicon chip, it
would help them a lot,” says Mammano.
So Teletype asked Silicon General to build a single IC that
would integrate the control functions for a switching power
supply. When presented with this request, Mammano and his
colleagues determined that there were no inherent reasons
why these functions could not be integrated on chip. “All the
individual blocks seemed compatible. That’s why I say it was
inevitable,” explained Mammano.
However, such an assessment belies the fact there were
serious technical challenges in putting all the PWM control
circuitry on a single chip. At that point in time, integrated
circuit design fell into two neatly divided camps—analog and
n hindsight, it sometimes seems that a great invention
evolved so logically from the existing technology and
so clearly answered pressing needs that its development was “inevitable.” That very word is the one Bob
Mammano uses to describe the creation of the first
pulse-width modulation (PWM) controller—the SG1524—
that he designed at Silicon General in 1975.
After all, switching power supplies (also known as
switchers or switched-mode power supplies [SMPSs]) were
being built using discrete components at least as far back as
the 1950s. And by the early 1970s, some of the individual
analog and digital functions needed to perform PWM—the
control technique commonly used to regulate the output
of the switching power supply—were becoming available
in IC form.
“An accident in time” is another way Mammano describes
the development of the SG1524. “Everybody knew that
switchers were a potential marketplace,” says Mammano. “It’s
just that [Silicon General] managed to get there first.”
Mammano recalls that both Motorola and Fairchild had
early versions of ICs that might be used in the switching
power supply application. Another chipmaker, Signetics, had
introduced the 555 timer and some engineers were using that
part in switching power supply designs.
However, Mammano observes, “No one had actually put
Photography by MISA/misaphoto.com
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LIFETIME ACHIEVEMENT AWARD
digital. The techniques for building logic circuits like flipdiscretely implemented PWM controllers.
flops in a gold-doped digital process were well understood.
Because the SG1524 demanded the monolithic integraSo too, the industry knew how to build op amps and other
tion of analog and digital functions, it became not only the
analog functions in a bipolar semiconductor process. But
first PWM controller, but on a broader scale, what Mamto develop a PWM controller on chip, it would be necesmano believes to be the first truly mixed-mode integrated
sary to build both analog and digital functions in the same
circuit. Mammano’s controller design also pioneered the
semiconductor process.
implementation of protection, as well as control, on chip.
The voltage and current levels required of the analog funcThis combination of protection and control features became
tions demanded that the chip be built in a bipolar process.
a mainstay of all future power controllers.
So Mammano explains, the main challenge in developing
Although the specific feature of current limiting had
the controller became, “How do we build the digital circuits
already been used in linear regulator ICs, the SG1524 was
on an analog process? To do
unique in that it limited output
that we had to go back to some
current on a pulse-by-pulse
pretty archaic digital logic techbasis, a requirement for switchnology that had been done with
ing regulators. And while the
basic bipolar technology.”
concept was first applied in the
To build the SG1524, Silicon
SG1524, Mammano notes that
General used what’s described
the techniques used to perform
as a 10-µm bipolar process
pulse-by-pulse current limiting
with a single metal layer. This
were much improved in later
process could handle high voltdevices.
age and relatively high current,
Although the SG1524 would
and could implement both npn
take cost out of the SMPS deand pnp transistors for level
sign, the device itself was not
shifting. “Another benefit of
cheap. Those first controllers
using the bipolar process was
were priced somewhere in the
that we learned to combine two
vicinity of $5 to $10 per unit in
different junction diodes to get
1976. However, as semiconduca good (for that time) temperator-manufacturing techniques
ture-compensated zener diode
progressed, the cost of proreference, a critical part of any
ducing a PWM controller fell
voltage regulator product,” says
dramatically. Rich Valley, vice
Mammano.
president of Texas Instruments’
And while designing each of Mammano’s PWM controller IC and its descendents reduced System Power Management
the blocks within the control- the size and cost of SMPSs, making them usable in countless business, notes that the same
ler was not easy, there was the applications.
function found in the SG1524
additional challenge of putting all the functions together
is available for less than 25 cents today.
on one chip with just 16 pins of I/O. That challenge fell to
As with many IC designs, development of the SG1524
IC layout designer Steve Jensen whom Mammano credits
required give and take between the chipmaker and its
as making a major contribution to the development of the
customer. “One of our tasks in designing the SG1524 was
SG1524. Mammano estimates that it took about a year to
to take Teletype’s specific requirements and to generalize
go from concept to first silicon.
them so that the same product could be applicable to the
In the end, the SG1524 broke new ground in several
rest of the world.” According to Mammano, the Teletype
ways. By integrating the PWM control functions on chip,
engineers asked for features such as a switching frequency
the controller removed much of the complexity from SMPS
up to 100 kHz, the ability to drive external power devices
design. Switching power supplies had long been valued for
(bipolar transistors then) with reasonable amounts of curtheir greater efficiency, their lighter weight and smaller size
rent, reasonable voltage accuracy, and the ability to close the
when compared with existing linear-transformer-based
feedback loop with an error amplifier that had a reasonable
power supplies. However, SMPSs had the drawbacks assoamount of gain.
ciated with greater complexity. That is, they cost more and
In the end, the SG1524 not only satisfied Teletype’s rewere less reliable than linears. (They also generated more
quirements, it met the basic performance requirements of
noise than linears, but that aspect of performance would be
many other SMPS and switching regulator applications. But
addressed in the application.) As the first monolithic PWM
gaining widespread acceptance for the first PWM controller
controller, the SG1524 greatly lessened the cost burden of
did not happen overnight. Silicon General was a relatively
building a switcher, while also improving reliability over
small company, and many customers would not allow the
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development of their systems to ride on the ability of such a
company to deliver a critical single-sourced device.
In time, there would be proven high-volume production
on the SG1524 at Silicon General and, later, the soughtafter second sources. But before any of that could happen,
potential users of the SG1524 needed to test out the device
in their designs.
ply voltage had reached the needed minimum level. (The
SG1524 was designed to operate off of a supply above 5 V.)
Later, Silicon General spun off protection circuits developed
for the SG1524 into the SG1543, a dedicated power supply
monitoring device.
Convincing engineers of the controller’s performance was
one matter, but convincing customers to trust their designs
with a single-sourced device from a small company was
another. In the beginning, Silicon General had just a small
initial order from Teletype and small orders from others who
used parts for prototyping or limited production runs.
However, acceptance of the SG1524 seemed to reach a
turning point when Silicon General convinced the power
supply design group within Digital Equipment Corp. (DEC)
to adopt the SG1524 in its designs. The order from this major
computer maker represented the first big production contract for the PWM controller.
DEC also inspired a secondgeneration version of the PWM
controller, the SG1525. This device incorporated a number of
improvements such as a bigger
output stage capable of handling
more current. This stage consisted
of a totem pole output driver,
which could be used to drive
the power MOSFETs that were
just then becoming popular. The
MOSFET gates required high
pulse currents in both directions
to turn them on and off. The totem pole output on the SG1525
could perform that task nicely.
Making a Big Splash
As Mammano recalls, he and his colleagues at Silicon
General did not know how great an impact the SG1524
would make. However, they did believe that power supply
designers would be interested in getting their hands on the
very first PWM controller chips. Anticipating that interest,
the company planned a “big, splashy introduction for the
SG1524.”
Mammano himself introduced
the device in June of 1976 at the
PowerCon convention, where he
presented the first technical paper
describing the chip’s operation.
Mammano came to the conference
with “a bucketful” of controller
chip samples in hand, he says. After presenting the paper in which
he described the new controller,
Mammano offered samples to the
conference attendees. At that point,
Mammano recalls, “Half the audience charged to the front” to get
samples of the chip.
In general, there was a widespread interest in the SG1524 and
the company gave out thousands
of samples to customers. Years
Building the Business of
later, many of those customers
Analog and Power ICs
told Mammano they had built Although Mammano viewed the integration of the
The opportunity to design
successful power supply designs PWM controller as something that was “inevitable,” his a groundbreaking chip like the
design of the SG1524 regulating pulse-width modulawith those early chips. But MamSG1524 might not have come
tor overcame the challenges of building digital and
mano readily admits there were analog circuits in the same semiconductor process. In Mammano’s way were it not
“lots of complaints” about the so doing, Mammano designed the first truly mixedfor his involvement in foundchip’s shortcomings. And Silicon signal IC, while ushering in the era of switching regu- ing Silicon General. As its first
General made many post-produc- lators and switched-mode power supplies.
vice president of engineering,
tion design changes to fix problems
Mammano along with Verda
that hadn’t been anticipated in the original design. In some
Hinkle, as vice president of manufacturing, and James
instances, problems identified by customers led to innovative
Johnson, as president, formed Silicon General, because
improvements in the controller design.
they perceived a need for analog products targeting military
“One customer found out that when he turned the power
applications.
supply on very slowly, you could get into a situation where
In his previous job at Autonetics, a division of North
both outputs, which were supposed to alternate back and
American Aviation, Mammano designed circuits for military
forth, came on together,” says Mammano. “And that was a
projects. As a designer, he found that most semiconductor
pretty good recipe for blowing up the power supply.”
manufacturers were primarily building integrated circuits
To prevent this problem from happening, Mammano
for the computer market. As a result, their emphasis was on
went back to the lab and designed what became the first
developing logic circuits and they offered little in the way
on-chip undervoltage lockout (UVLO) circuit. The UVLO
of analog functions.
did not allow the controller to turn on before the sup“We were looking for analog products to go in our power
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LIFETIME ACHIEVEMENT AWARD
supplies—voltage regulators, amplifiers and various specialized controls,” Mammano explains. “But we weren’t getting
much support from the semiconductor people, even though
we were willing to pay a lot of money for them. We just
didn’t use many devices.” Based on that experience, Mammano and his colleagues concluded there would be good
potential in a company focused on developing analog chips
for the military.
However, soon after Silicon
General was started in Westminster, Calif., in 1969, the military
aerospace industry went into a tailspin, taking with it potential orders
for analog ICs. As a result, Mammano and his Silicon General
cofounders refocused the new company on developing power
management products for commercial markets.
Mammano’s experience at Autonetics in the early 1960s
not only inspired the founding of Silicon General, it also
introduced him to the concept of switching power. One of his
assignments at Autonetics was to design a switching power
supply that would be used to power a militarized airborne
computer. A switcher was needed because a linear supply
would have been too heavy.
Although the SMPS Mammano designed was significantly
better than a linear in terms of the watts per pound, the
switcher itself would not qualify as light by today’s standards.
The power supply was based on a magnetic amplifier design
that employed many toroidal transformers. With the supply
operating at a switching frequency of 20 kHz to 40 kHz, these
transformers required large, hand-wound cores. In addition
to its significant mass, the SMPS was also quite expensive and
a look at the semiconductor content in that supply reveals
why. Mammano recalls that the design employed silicon
bipolar power transistors made by Texas Instruments. Those
transistors cost $125 each.
Through this experience at Autonetics, Mammano
learned the underlying control principles he would later be
asked to implement on chip. But it’s also likely that his work
on these complicated, heavy and expensive SMPSs drove
home the point that here was an application that could truly
benefit from silicon integration.
No doubt these same lessons were applied again when
Mammano, Hinkle and Arthur Bruno, a former CEO of
Silicon General, left that company to create a power IC
division within Unitrode Corp. Already established as a
manufacturer of power discretes, Unitrode wanted an IC
division to complete its power semiconductor portfolio
when the threesome set up shop for the IC division in 1981
at a facility in Merrimack, N.H.
At Unitrode, Mammano took on more of a management
role. Consequently, his focus shifted from designing new
power circuits to helping define them. Mammano guided
product development on new power ICs that would, like
the SG1524, establish trends in the industry. For example,
under Mammano’s guidance, Unitrode introduced the
first PWM controllers with current-mode control. Two
of these controllers, the UC1846 and UC1843, ultimately
became two of the most popular power supply controllers
in the industry.
From Designer to Teacher
Rather than designing the new chips himself at Unitrode,
Mammano served as mentor to the next generation of power
Mammano continues to play a role in efforts to advance
the state of the art in power supply design.
www.powerelectronics.com
IC designers within the company. However, his role as a
teacher extended well beyond his company’s engineering lab.
Soon after joining Unitrode, Mammano began participating in company-sponsored seminars that addressed power
supply design from both the power control side and the
power device side. When Texas Instruments (TI) acquired
Unitrode in the late 1990s, these seminars continued—a
testament to their popularity. Through the years, Mammano
has continued to teach young power supply designers in
these seminars.
Looking Ahead
At a time when many of his contemporaries have retired,
Mammano continues to play an active role in the power
electronics industry. He still teaches seminars, and as a staff
technologist helps to shape power IC development, even
occasionally meeting with customers. Mammano also participates in industry forums such as the energy efficiency
committee within the Power Sources Manufacturers Association. This group helped the U.S. Environmental Protection
Agency to develop its energy efficiency standards for external
power supplies.
Mammano continues to play a role in efforts to advance
the state of the art in power supply design. Recently, Mammano has been involved with TI’s efforts to develop power
ICs that employ digital control techniques. Mammano comments, “This is a new challenge for us. It’s an opportunity
for us to develop many interesting new products, which we
think will mean a lot to customers.” But, he explains that
this opportunity comes with some concerns because digital
power control adds complexity, which in turn requires use
of a more-dense semiconductor process. That requirement
adds to the cost of fabricating the chip as well as to the cost
of developing it.
Mammano sums up the challenge of digital power control
as one of “defining our products in a way that represents
significant value to a broad base of customers so that we have
both the volume in the product to drive the manufacturing
costs down, and the economies that result from living within
the process limitations.” No doubt, these are issues Mammano has confronted many times in the past as he worked
to develop the ICs that have paved the way for this newest
generation of power controllers.
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