1. DC/DC Switching Power Converter with Radiation Hardened Digital Control Based on SRAM FPGAs F. Baronti 1, P.C. Adell 2, W.T. Holman 2, R.D. Schrimpf 2, L.W. Massengill 2, A.F. Witulski 2, M. Ceschia 3 1 University of Pisa, Dept. Inf. Eng., Pisa, Italy 2 Vanderbilt University Institute for Space and Defense Electronics, Nashville, TN, USA 3 University of Padova, Dept. Inf. Eng., Padova, Italy DC/DC switching converters are essential components for a satellite Power Control Unit. Digital control vs. analog control  Increased flexibility, reduced sensitivity to noise, reduced sensitivity to component parameter variations  More complex control algorithm  Easier to harden against radiation COTS SRAM-FPGA implementation of the digital controller  Higher density, lower cost, and faster turn- around time compared to ASICs  Reconfigurability (on-orbit design changes)  High sensitivity to single event effects Introduction Single Event Functional Interrupt (SEFI) is the dominant radiation- induced error in SRAM FPGAs: 1 Design of a digitally controlled boost converter Radiation hardening of the digital controller Single event functional interrupts are the dominant radiation error effect in SRAM- based FPGAs. A SEFI-hardened DC/DC switching power converter (boost topology) has successfully been implemented using a reconfigurable digital control loop based on FPGAs. Dual redundant self-mitigation technique has been applied to the converter to mitigate and correct SEFIs. An efficient approach has been applied to resynchronize the two FPGAs after the occurrence of a SEFI. The design has successfully been validated through VHDL simulation and experiments. MAPLD 2004 Conclusion Results High-efficiency switching boost converter steps up an unregulated input voltage to a regulated output voltage. The feedback loop is implemented using an ADC and an SRAM-based FPGA to digitally control the duty cycle D and regulate the output over a wide range of input voltages and load conditions. 1 bit resolution ADC (comparator) Up/down counter implements the digital controller Digital Pulse Width Modulator generates the MOSFET switching signal Simple design, low power consumption The use of a deadzone comparator avoids undesired oscillations SEFI causes missing pulses in the generated PWM control signal of the converter Large transient drop at the converter output Use of a Radiation Hardness By Design (RHBD) technique to mitigate and correct SEFI Dual redundant approach at both logic design and device levels SEFI Detection:  Each FPGA continuously monitors the status of the other FPGA  A SEFI occurrence is detected when an FPGA remains in the Offline status for too long SEFI Correction: two steps are necessary  Reload configuration bitstream  Resynchronization of the two FPGAs. Two options can be followed: Reset both devices (RHBD w/ reset)  Disruption of current state for both devices results in interruption of converter feedback loop.  Undesirable transient pulse at the converter output results. Reconfigured device loads current state from working device (RHBD w/ resync.)  Converter output is not affected since working device maintains the feedback loop.  Requires additional logic to implement.  Configuration memory bit flip  Low LET th = 0.1 - 0.5 MeV cm 2 /mg  Full functionality recovered by reconfiguring the device Dual redundant self-mitigating technique VHDL simulation Recfg. emul. block forces the FPGA output to hi-Z status and initiates a reset at the end of the reconfiguration phase The error inj. block permits simulation of an SEFI occurrence in order to validate design SEFI injected on FPGA 1 FGGA 1 output goes to Hi-Z state FPGA 2 detects the invalid status of FPGA 1 and forces its reconfiguration After the reconfiguration and synchronization phases, FPGA 1 restarts operation with correct duty cycle Test-bed architecture Measured converter output Very large output voltage drop for the conventional unhardened design Reduced (but unacceptable) voltage drop for RHBD w/reset design No voltage drop for RHBD w/ resync. design 2 1 1 Hi-Z 1 0 1 1 1 1 1 1 0 10 0 Offline FPGA 1 FPGA 2 The error doesn’t propagate to the output Recovery from an SEFI occurrence: Error detection and correction logic Deadzone comparator 3 4 5