ISR2805DDRH データシートの表示（PDF） - M.S. Kennedy

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ISR2805DDRH

RADIATION HARDENED HIGH-POWER, HIGH EFFICIENCY DC-DC POWER CONVERTER

M.S. Kennedy 

APPLICATION NOTES CONT'D

RADIATION PERFORMANCE

MSK converters give you superior radiation performance with-

out the highs and lows of using "typical" DC-DC converters. The

design represents a break from the traditional hardening method

of simply replacing commercial die elements with radiation screened

die in an off-the-shelf DC-DC converter design.

Special design techniques implemented at both the module

level and the transistor circuit element level were used to harden

the DC-DC converters. Here are some of the engineering steps

taken to guarantee the radiation performance.

TOTAL DOSE HARDNESS:

The converters employ a fully magnetically-isolated configura-

tion allowing the positive converter output to be regulated directly

without the use of opto-couplers. Galvanic isolation between in-

put and output is provided by the flyback converter and a small

gate-drive transformer which couples the PWM drive signal to the

main switching MOSFET. This approach provides optimum out-

put voltage regulation and avoids the gain degrading effects of

total ionizing dose on opto-couplers which can result in converter

failure.

SINGLE-EVENT EFFECTS HARDNESS:

All critical ICs in the converter use a latch-up immune,

dielectrically-isolated, BiCMOS process that prevents converter

components from entering a potentially catastrophic latched state.

The heart of the DC-DC converter is the Single-Event Effects

hardened PWM. The chip has SEU-immune CMOS soft-start con-

trol logic which will not upset in a heavy ion environment. The on-

chip overcurrent comparator employs a redundant cross-checking

comparator design. Error amp circuitry incorporates redundant

wire OR differential input stages which prevent the amplifier out-

put from over-ranging, which could cause excessive output pulse

widths leading to overcurrent fault sequencing, transformer core

saturation or power switch overstress. The toggle Flip/Flop (F/F)

and all pulse control logic functions have been designed in SEU-

immune CMOS to keep pulse phase integrity from being upset.

The PWM used in the flyback circuitry incorporates these

same improvements with the exception of the soft-start func-

tion.

DC-DC converters use comparator ICs to control various

converter functions such as input inrush current limiting, input

undervoltage lockout, start-up regulator shutdown, output ov-

ervoltage protection, and main/auxiliary output voltage sequenc-

ing. A high-energy ion striking the comparator can cause any

of these functions to fail or inadvertantly activate causing un-

wanted power supply interruptions. The MSK converters em-

ploy a new hardened, SEU immune, quad comparator. The

chip uses triple redundant bipolar comparators for analog preci-

sion, and is backed by SEU-immune voting logic which ensures

that no single-particle error can propagate to the output.

The potential for catastrophic single-event gate rupture in

MOSFET's has led to the development of MOSFET's with ox-

ide structures which resist breakdown up to fully rated MOSFET

voltage potential under fully off-biased conditions. All MOSFET's

used in the converters mitigate Single-Event Gate Rupture ef-

fects up to 82 MeV-cm²/mg.

A PROVEN DESIGN METHODOLOGY

The power supplies were developed using a proven, conserva-

tive design methodology which includes selecting radiation-hard-

ened and established reliability components and fully de-rated to

the requirements of MIL-STD-975, MIL-STD-1547 and GSFC PPL-

21 Appendix B. Proprietary radiation-hardened silicon gate (RSG)

process for integrated circuits ensures total dose capability to

300krads and immunity to single-event latch-up (SEL). Radiation-

hardened power MOSFETs virtually eliminate the possibility of

single-event gate rupture and single-event burn-out. Direct regu-

lation is utilized instead of opto-couplers to minimize temperature,

radiation and aging sensitivity. The Cadence Analog Work Bench

(AWB) tool set, including Sensitivity/Worst Case and Monte Carlo

tools, was used extensively to predict and optimize circuit perfor-

mance for both beginning and end-of-life. Thorough design analy-

sis include Worst Case, Component Stress and Reliability (MTBF).

MSK's DC-DC converters offer high reliability through "tried

and true" methods of passive component procurement and hybrid

construction techniques. All stacked capacitors are procured, pre-

assembled (stacked) and up screened by the capacitor manufac-

turer. Capacitor mounting procedures are performed per the

supplier's guidelines. Magnetics, resistors and capacitors are all

procured to the highest standards. Full component level traceabil-

ity is maintained on all high-rel lots. Final hybrid assembly and

screening is available up to MIL-PRF-38534 Class K or Class H

requirements.

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PRELIMINARY Rev. - 3/01

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