Malik E. Elbuluk

University of Akron, Akron, Ohio

Scott Gerber

ZIN Technology, Brook Park, Ohio

Ahmad Hammoud

QSS Group, Inc., Brook Park, Ohio

Richard Patterson and Eric Overton

Glenn Research Center, Cleveland, Ohio

Performance of High-Speed PWM Control

Chips at Cryogenic Temperatures

NASA/TM—2001-211123

September 2001
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NASA/TM—2001-211123

September 2001

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

2001 Industry Applications Society Annual Meeting

sponsored by the Institute of Electrical and Electronics Engineers

Chicago, Illinois, September 30–October 5, 2001

Performance of High-Speed PWM Control

Chips at Cryogenic Temperatures

Malik E. Elbuluk

University of Akron, Akron, Ohio

Scott Gerber

ZIN Technology, Brook Park, Ohio

Ahmad Hammoud

QSS Group, Inc., Brook Park, Ohio

Richard Patterson and Eric Overton

Glenn Research Center, Cleveland, Ohio
Acknowledgments

This work was supported by the NASA Glenn Research Center, Contract NAS3–00145, GESS Task 0020, and by

JPL’s NASA Electronic Parts and Packaging Program (NEPP).

Available from

NASA Center for Aerospace Information

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This report contains preliminary

findings, subject to revision as

analysis proceeds.

Available electronically at http://gltrs.grc.nasa.gov/GLTRS
Performance of High-Speed PWM Control Chips at 

Cryogenic Temperatures 

Malik E. Elbuluk 

University of Akron 

Akron, Ohio 44325

Ahmad Hammoud 

QSS Group, Inc. 

Brook Park, Ohio 44142 

Scott Gerber 

ZIN Technology 

Brook Park, Ohio 44142 

Richard Patterson and Eric Overton 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135

Abstract- Planetary exploration missions and deep space 

probes require electronics capable of low temperature 

operation. Such electronics will not only improve circuit 

performance and reliability, but also increase system 

efficiency, and reduce development and launch costs. DC/DC 

converters are an essential part of most aerospace power 

management distribution systems (PMAD). Therefore, 

DC/DC converters that can operate at cryogenic 

temperatures are crucial for space missions where low 

temperatures are encountered. An important component of a 

DC/DC converter is the pulse width modulation (PWM) chip 

that provides the control to the converter main switches. 

 In the process of designing low temperature DC/DC 

converters, experimental investigations were performed to 

evaluate the performance of a number of high-speed PWM 

chips as a function of temperature in the range of 25 °C to 

–190 °C. These integrated circuit (IC) chips ranged in their 

electrical characteristics, modes of control, packaging options, 

and applications. This paper presents and discusses the 

experimental procedures along with the experimental data 

obtained on the investigated chips. 

1. INTRODUCTION

Future space missions, such as outer planetary 

exploration and deep space probes, require electrical 

power management systems that operate reliably and 

efficiently in very low temperature environments. For 

example, inter-planetary probe launched to explore the 

rings of Saturn would experience an average temperature 

of about –183 °C. 

Presently, spacecraft operating in the cold environment 

of deep space carry a large number of radioisotope heating 

units (RHU) to maintain temperature for the on-board 

electronics at approximately 20 °C [1]. This is not an ideal 

solution because the RHUs are always producing heat, 

even when the spacecraft is already too hot, thus requiring 

an active thermal control system for the spacecraft. In 

addition, they are very expensive and require elaborate 

containment structures. Electronics capable of operation at 

cryogenic temperatures will not only tolerate the hostile 

environment of deep space but also reduce system size 

and weight by eliminating radioisotope heating units 

and associated structures; thereby reducing system 

development and launch costs, improving reliability and 

increasing energy densities. 

2. POWER ELECTRONICS AT CRYOGENIC TEMPERATURES 

Power electronic circuits designed for operation at low 

temperature are expected to result in more efficient 

systems than those at room temperature. This improvement 

results from better electronic, electrical, and thermal 

properties of materials at low temperatures [2,3]. In 

particular, the performance of certain semiconductor 

devices improves with decreasing temperature down to 

liquid nitrogen temperature (–196o

C) [3,4]. At low 

temperatures, majority carrier devices demonstrate reduced 

leakage current and reduced latch-up susceptibility. In 

addition, these devices show higher speed resulting from 

increased carrier mobility and saturation velocity [3-5]. 

An example is the power MOSFET that has lower 

conduction losses at low temperature due to the reduction 

in the drain-to-source resistance RDS(on) resulting from 

increased carrier mobility [4,6,7]. 

The Low Temperature Electronics Program at the 

NASA Glenn Research Center focuses on research and 

development of electrical components and systems suitable 

for applications in deep space missions [8]. Research is 

being conducted on devices and systems for use down to 

cryogenic temperatures. Some of the components that are 

being characterized include semiconductor switching 

devices, resistors, magnetics, and capacitors [9-11]. A 

number of commercial-off-the-shelf modular, low power 

DC/DC converters, with specifications that might fit the 

requirements of specific future space missions, have been 

tested. These converters, which ranged in electrical power 

from 8 W to 13 W and output voltage from 3.3 V to 12 V, 

were characterized in terms of their performance as a 

function of temperature in the range of 20 °C to –190 °C 

[12-14]. 

Efforts are in progress to build modular DC/DC 

converters with low temperature capabilities. The 

converters will be designed or modified to operate from 

room temperature to –196 °C using commercially available 

or newly developed components such as CMOS-type 

NASA/TM— 2001-211123 1
NASA/TM—2001-211123 2 

devices and MOSFET switches. PWM IC chips will be 

used to implement the closed-loop control of the 

converters. 

In this work, a preliminary evaluation of the 

performance of four high-speed PWM chips has been 

conducted as a function of temperature in the range of 

25 °C to –190 °C. These chips ranged in their electrical 

characteristics, modes of control, packaging options, and 

applications. The experimental procedures along with the 

experimental data obtained on the investigated chips are 

presented and discussed. 

3. SPACE POWER AND ADVANCES IN DC/DC CONVERTERS

Most aerospace power management systems are DCbased and thus require DC/DC power converters that will 

operate over a wide input voltage range to produce an 

output voltage between 1.5 V to 15 V at various power 

levels. 

Recently, there has been a tremendous progress in the 

design of high power density DC/DC converters. 

Converters that operate at power densities of 50% or 

higher than the available standard conventional converter 

designs have been developed. This increase in power 

density is achieved using new designs, advanced devices 

and components, and packaging techniques. For example, 

the newly developed synchronous rectifier-based DC/DC 

converter modules with multi-layer thick-film hybrid 

packaging provide, without the use of a heat sink, more 

usable output power than the conventional, schottky diode 

based converters with a heat sink and thick-film single 

layer packaging. As the demand to achieve high power 

density of DC/DC converters increases, there is a need to 

provide more integration and, therefore, the role of highly 

functional PWM control chips will increase. 

4. INTEGRATED CIRCUITS PWM CONTROLLERS

Electronic control of DC/DC converter power circuits 

is achieved by modulating the duty ratio (D) of the 

controlled switch, defined as the ratio of its ON-time to the 

switching period. Typically, the intent is to keep the 

output voltage constant, as determined by a DC reference 

signal , in the presence of time-varying sources and loads. 

The technique of modulating the duration (or width) of the 

ON-time (or pulses) that is applied to the drive circuit of 

the controlled switch is called “Pulse Width Modulation”

(PWM). 

Fig. 1 shows a simple PWM controller circuit that 

controls the switch operation in a DC/DC converter. A 

sawtooth signal with a fixed frequency and a fixed 

amplitude (VR) is applied to the PWM comparator whose 

second input is fed from the output of an error amplifier 

(Ve) that compares a reference voltage to the output 

voltage (VOUT). The output of the latch gives the required 

PWM signal. This control technique is known as the 

“voltage-mode” PWM control because only the voltage 

information is used [15]. 

It is shown that the utilization of both voltage and 

current feedback adds significant advantage to the stability 

of closed-loop PWM controllers. One way of adding the 

current information is to use the switching analog current 

waveform in place of the sawtooth generator. The analog 

voltage of the switching current waveform is usually 

provided with a small current-sense resistor placed in 

series with the switch. This control technique is called 

“current-mode” control and is shown in Fig. 2 [15]. 

Fig. 1 Voltage-mode PWM control technique 

Fig. 2 Current-mode PWM control technique 

 The fundamental challenge of DC/DC converter design 

is to simultaneously realize, two difficult objectives: good 

electrical performance and low cost. A large number of 

fully integrated PWM circuits, available from a number of 

manufacturers are designed to meet these objectives. In 

particular, fixed frequency PWM controllers are by far the 

devices that are widely used. There have been many ways 

of implementing fixed frequency PWM control. The basic 

ingredients of all PWM integrated circuit controllers 

contain an adjustable clock for setting the oscillator 

frequency, an output voltage error amplifier, a voltage 

reference, a signal generator for providing a sawtooth 

waveform synchronized with the clock, and a comparator 

to compare the error amplifier output signal with the 

sawtooth signal. The output signal from the comparator is 
NASA/TM—2001-211123 3 

used to drive the controlled switch directly or through a 

discrete or integrated drive circuit. There has been a large 

number of PWM integrated circuit manufacturers using 

different technologies such as all bipolar, BiCMOS or all 

CMOS which provide all the necessary features to 

implement fixed frequency control with a minimal external 

parts count. Moreover, these control chips contain features 

such as current limiting, over-voltage protection, input 

under-voltage protection plus primary and auxiliary 

functions that may improve the performance of the 

controller. An example of a typical PWM chip is shown in 

Fig. 3a. Fig. 3b shows the circuit configuration used in 

testing the performance of the chip. The operating 

frequency of these chips range from a few kHz to a few 

MHz [15]. 

5. LOW TEMPERATURE EXPERIMENTAL SETUP

A preliminary evaluation of the performance of a 

number of high-speed PWM control ICs with different 

packages and ratings, acquired from various 

manufacturers, was conducted as a function of temperature 

from 20 °C to –190 °C. At a given temperature, the 

internal voltage reference, and the oscillator and the device 

modulated outputs were observed. The tests were 

performed in a Sun Systems environmental chamber 

utilizing liquid nitrogen as the coolant. A temperature rate 

of change of 10 °C/min was used throughout this work. At 

every test temperature, the device under test was allowed 

to soak at that temperature for a period of 30 minutes 

before any measurements were made. After the last 

measurement was taken at the lowest temperature, the 

chips were allowed to stabilize to room temperature and 

then the measurements were repeated at room temperature 

to determine the residual effect of the low temperature 

exposure. 

 (a) Circuit schematic

(b) Laboratory test circuit 

Fig. 3 PWM current-mode control chip

6. RESULTS AND DISCUSSIONS

Four PWM chips were evaluated under various test 

parameters. Only selected data, which best represents the 

performance of the devices at low temperature, is 

presented in this paper. Table 1 gives a comparative list 

outlining the main features of each of the chips tested. The 

functionality of each chip at low temperature is evaluated 

by observing the waveforms of its internal voltage 

reference, the oscillator frequency and the PWM output. 

In order to evaluate the chip functionality, a number of 

external components were required. In the case of chips 1, 

2 and 3, the tests were performed with only the chip inside 

the chamber and the rest of the components outside the 

chamber. Chip 4, on the other hand, was located on a 

surface mount evaluation-board, which made separating 

the components difficult. As a result, the evaluation-board 

containing chip 4, as a whole, was tested inside the 

chamber. 

Table 2 shows the variation of the operating frequency 

for each chip as a function of temperature. It can be seen 

that chip 1 frequency stayed fairly constant initially but 

changed considerably as the temperature was lowered 

below –80 °C. This chip failed to operate for temperatures 

below –140 °C. Chip 2 maintained fairly constant 

frequency down to its lowest operating temperature of 

–180 °C. Similarly, chip 3 maintained fairly constant 

frequency down to its lowest operating temperature of 

–100 °C. The evaluation-board containing chip 4, on the 

other hand, displayed considerable change in frequency as 

the temperature was lowered down to its lowest at 

–140 °C. The reason for this could be deviation of some 

of the external components connected around the chip. 

TABLE 1 

 SUMMARY OF PWM IC FEATURES 

Chip 1 2 3 4 

Technology Bipolar BiCMOS Bipolar BiCMOS 

Packaging Dip Dip Dip SOIC 

Lowest 

Temperature 0 °C -55 °C -40 °C 0 °C 

Maximum 

Frequency 500 kHz 1 MHz 500 kHz 5 MHz 

Duty Cycle 

Range 0 - 100% 0 - 100% 0 - 50% 0 - 100% 

PWM Outputs One One Two Two 

Control Mode Current Current Voltage Voltage 
NASA/TM—2001-211123 4 

TABLE 2 

 VARIATION OF CHIP FREQUENCY WITH TEMPERATURE 

Temp. Chip 1 Chip 2 Chip 3 Chip 4 

25 °C 87 kHz 67 kHz 95 kHz 40 kHz 

0 °C 89 kHz 67 kHz 97 kHz 39 kHz 

-20 °C 91 kHz 67 kHz 98 kHz 41 kHz 

-40 °C 93 kHz 68 kHz 98 kHz 43 kHz 

-60 °C 94 kHz 68 kHz 95 kHz 47 kHz 

-80 °C 94 kHz 68 kHz 97 kHz 50 kHz 

-100 °C 57 kHz 69 kHz 98 kHz 51 kHz 

-120 °C 54 kHz 68 kHz --------- 77 kHz 

-140 °C 51 kHz 69 kHz --------- 108 kHz 

-160 °C -------- 69 kHz ----------- ------- 

-180 °C -------- 70 kHz ---------- -------- 

Figures 4 through 7 show the waveforms of the four 

chips. Figure 4 shows the waveforms for chip 1 at room 

temperature (25 °C) and at the lowest operating 

temperature (–140o

C). It can be seen that the reference 

voltage maintained its value of 5 V throughout the low 

temperature test. The frequency of the oscillator and the 

PWM output dropped significantly at the lower 

temperatures. Also, multiple switching occurred in the 

PWM output at the lowest operating temperature. 

Figure 5 shows the performance of chip 2 at room 

temperature and at –180 o

C (the lowest temperature). This 

chip is a modification of chip 1 by incorporating BiCMOS 

technology and a wider temperature operating range, as 

seen in Table 1. The frequency and duty cycle maintained 

their values over the temperature range. However, in the 

PWM output some pulses skipped at the lowest 

temperature. Comparing the two traces of the PWM output 

in Figure 5b, the top trace is similar to that at room 

temperature but some pulses were skipped in the bottom 

trace. 

 

Figure 6 shows the reference voltage, the two PWM 

outputs and the oscillator waveform for chip 3. Figure 6a 

shows the performance at room temperature and Figure 6b 

shows the performance at the lower temperature of 

–100 o

C. Compared to room temperature, the performance 

at –100 o

C shows multiple switching in output B and also a 

very noticeable change in the dead time for switching 

between the two outputs A and B. Except for a few spikes, 

the reference voltage maintained its value between the two 

temperature extremes. 

The performance of chip 4 at room temperature and at 

–140 o

C is shown in Figures 7a and 7b, respectively. It can 

be clearly seen that the reference voltage remained 

relatively stable but the operating frequency and duty ratio 

changed considerably. The dead time, however, did not 

exhibit much change with temperature. 

7. CONCLUSIONS

An experimental investigation has been performed to 

evaluate the performance of four high-speed pulse width 

modulation chips as a function of temperature in the range 

of 25 °C to –190 °C. The chips ranged in their electrical 

characteristics, modes of control, packaging options, and 

applications. In general, all of the chips exceeded their 

manufacturer’s low temperature limit. The degree of 

operational stability of the chips with temperature varied 

from one device to another. Long term testing at cryogenic 

temperatures, however, is needed to fully characterize 

these and other devices for potential use in low 

temperature applications. 
NASA/TM— 2001-211123 

(2 V/div)

(2 V/div)

(5 us/div)

(a)

(5 V/div)

(2 V/div)

(2 V/div)

(5 us/div)

(b)

(5 V/div)

Reference

Reference

O scillator O scillator

PW M Outp u t PW M Outp u t

Fig. 4 Performance of chip 1: (a) at room temperature (b) at low temperature of – 140 °C. 

(2 V/div)

(2 V/div)

(5 us/div)

(a)

(5 V/div)

(2 V/div)

(2 V/div)

(5 us/div)

(b)

(5 V/div)

Reference

Reference

O scillator O scillator

PWM Outp u t PWM Outp u t (5 V/div)

PWM Outp ut w ith skip p ed p ulses

Fig. 5 Performance of chip 2: (a) at room temperature (b) at low temperature of – 180 °C. 

5
NASA/TM— 2001-211123 

(2 V/div)

(5 V/div)

(5 V/div)

(2 V/div)

(5 V/div)

(5 V/div)

(2 us/div)

(a)

(5 V/div)

(2 us/div)

(b)

Reference Reference

Outp ut A Outp ut A

Outp ut B

Outp ut B

O scillator O scillator

Fig. 6 Performance of chip 3: (a) at room temperature (b) at low temperature of – 100 °C. 

(2 V/div)

(5 V/div)

(5 us/div)

(a)

(5 V/div)

(2 V/div)

(5 V/div)

(5 us/div)

(b)

(5 V/div)

Reference Reference

Outp ut B Outp ut B

Outp ut A Outp ut A

Fig. 7 Performance of chip 4: (a) at room temperature (b) at low temperature of – 140 °C. 

6
NASA/TM—2001-211123 7

9. REFERENCES

1. Gerber, S., Patterson, R., Ray, B. and Stell, C., 

“Performance of a Spacecraft DC/DC Converter Breadboard 

Modified for Low Temperature Operation,” IECEC 96, 

Vol.1, 1996, pp. 592-598. 

2. Kirschman, R. K. “Low Temperature Electronic Device 

Operation”, 1991 Symp. Electrochemical Society, PV-14. 

3. Dean, M., Foty, D., Saks, N., Raider, S. and Oleszel, G., 

“Low Temperature Microelectronics: Opportunities and 

Challenges,” Proc. Symp. Low Temp. Electronic Device 

Operation, Electrochemical Society, Vol. 91-14, pp. 25-37. 

4. Ray, B., Gerber, S.S., Patterson, R.L. and Myers, I.T., 

“Power Control Electronics for Cryogenic Instrumentation,”

Advances in Inst. and Control, Vol. 50, Part 1, Int. Soc. for 

Measurement and Control, 1995, pp. 131-139. 

5. Krishman, R.K., “Cold Electronics: an Overview,”

Cryogenics, Vol. 25, No. 3, 1985, pp. 115-122. 

6. Mueller, O., “On-Resistance, Thermal Resistance and 

Reverse Recovery Time of Power MOSFETs at 77K,”

Cryogenics, Vol. 29, 1989, pp. 1006-1014. 

7. Ray, B., Gerber, S., Patterson, R. and Myers, I., “77K 

Operation of a Multi-Resonant Power Converter,” IEEE 

PESC’95 Record, Vol. 1, pp. 55-60. 

8. Patterson, R.L., Dickman, J.E., Hammoud, A. and Gerber 

S.S., “Low Temperature Power Electronics Program,”

NASA EEE Links, Electronic Packaging and Space Parts 

News, Vol. 4, No. 1, January 1998. 

9. Ray, B., Gerber, S.S. and Patterson, R.L., “Low 

Temperature Performance of a Full-Bridge DC-DC 

Converter," IECEC ‘96, Vol. 1, 1996, pp. 553-559. 

10. Patterson, R.L., Hammoud, A. and Gerber, S.S., 

“Evaluation of Capacitors at Cryogenic Temperatures for 

Space Applications,” IEEE International Conference on 

Electrical Insulation, Washington DC, June 7-10, 1998. 

11. Hammoud, A., Gerber, S.S, Patterson, R.L. and MacDonald, 

T., “Performance of Surface-Mount Ceramic and Solid 

Tantalum Capacitors for Cryogenic Applications,” IEEE 

Conference on Electrical Insulation and Dielectric 

Phenomena, Atlanta, GA, Oct. 25-28, 1998. 

12. M. Elbuluk, S. Gerber, A. Hammoud and R. Patterson 

“Characterization of Low Power DC/DC Converter 

Modules at Cryogenic Temperatures”, Proceedings of IEEE 

2000 IAS Annual Meeting (IAS’2000), Rome, Italy. 

13. M. Elbuluk, S. Gerber, A. Hammoud and R. Patterson, 

“Efficiency and Regulation of Commercial Low Power 

DC/DC Converter Modules at Low Temperatures”, 

Proceedings of ,” IECEC 2000. 

14. S. Gerber, A. Hammoud, R. Patterson, M. Elbuluk, 

“Performance Evaluation of Low Power DC/DC Converter 

Modules at Cryogenic Temperatures”, Proceedings of IEEE 

2000 Power Electronic Specialists Conference 

(PESC’2000), Galway, Ireland. 

15. “Power Supply Control Products”, Data Book, Texas 

Instrument, 2000. 
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E–12972

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13

Performance of High-Speed PWM Control Chips at Cryogenic Temperatures

Malik E. Elbuluk, Scott Gerber, Ahmad Hammoud,

Richard Patterson, and Eric Overton

DC/DC converters; PWM chips; Cryogenics; Integrated circuits

Unclassified -Unlimited

Subject Category: 33 Distribution: Nonstandard

Prepared for the 2001 Industry Applications Society Annual Meeting sponsored by the Institute of Electrical and Electronics Engineers,

Chicago, Illinois, September 30–October 5, 2001. Malik E. Elbuluk, University of Akron, 302 Buchtel Mall, Akron, Ohio 44325–0001

(work funded under NASA Contract NAS3–98008); Scott Gerber, ZIN Technology, 3000 Aerospace Parkway, Brook Park, Ohio 44142;

Ahmad Hammoud, QSS Group, Inc., 2000 Aerospace Parkway, Brook Park, Ohio 44142; Eric Overton and Richard Patterson, NASA

Glenn Research Center. Responsible person, Richard Patterson, organization code 5480, 216–433–8166.

The operation of power electronic systems at cryogenic temperatures is anticipated in many NASA space missions such

as planetary exploration and deep space probes. In addition to surviving the space hostile environment, electronics

capable of low temperature operation would contribute to improving circuit performance, increasing system efficiency,

and reducing development and launch costs. As part of the NASA Glenn Low Temperature Electronics Program, several

commercial high-speed Pulse Width Modulation (PWM) chips have been characterized in terms of their performance as

a function of temperature in the range of 25 to –196 °C (liquid nitrogen). These chips ranged in their electrical characteristics, modes of control, packaging options, and applications. The experimental procedures along with the experimental data obtained on the investigated chips are presented and discussed.