A radiation-tolerant LDO voltage regulator for HEP applications F.Faccio, P.Moreira, A.Marchioro, S.Velitchko CERN

Heidelberg LECC05F.Faccio – CERN/MIC Outline  Motivation  Specifications  Implementation  Measured performance  Radiation performance  Conclusion

Heidelberg LECC05F.Faccio – CERN/MIC Motivation  Power distribution in LHC experiments is a real challenge  Need for voltage regulation close to the electronics to be powered: linear regulators are often used  To limit (useless) power dissipation, LDO regulators are desired, having drop-out voltages as low as mV  Rad-hard regulators with these characteristics are prohibitively expensive  A rad-hard LDO regulator with limited current capability (300mA) can be developed as an ASIC using “our” quarter micron CMOS process at low cost!

Heidelberg LECC05F.Faccio – CERN/MIC Specifications MinTypMaxComment Output V (V) 2.5 Fixed in this version Input V (V) Output I (mA) Dropout V (mV) 150 At 300mA current Quiescent I (mA) 1 Over-V prot. (V) 3.5 Protects regulator itself Over-I prot. (mA) Switch to current regulation Over-T prot. ( o C) Disable in/out yes Possible to disable, output flag

Heidelberg LECC05F.Faccio – CERN/MIC Implementation (1)  Regulator named “CRTREG1”, as part of the CERN Radiation Tolerant (CRT) family of components  External compensation solution chosen: the dominant pole is the output pole  This imposes value (min. 1, suggested 6.6  F) and characteristics (low ESR of the order of 20mOhm) of the output compensation capacitance, but allows for larger regulator bandwidth, hence good PSRR and transient response  Integrated in 0.25  m CMOS technology using radiation-tolerant layout techniques

Heidelberg LECC05F.Faccio – CERN/MIC Implementation (2) Functional block diagram off Over-V monitor Over-T monitor Switches for disable Over-I monitor Error amplifier R1 R2 Bandgap VinVout Gnd Disable in Disable flag

Heidelberg LECC05F.Faccio – CERN/MIC Implementation (3)  Chip size: 2x2mm  Multiple pads for input and output current  Mounted on a very compact plastic package (4.9 x 6.1 x 1.6 mm), 16L-EPP-SSOP

Heidelberg LECC05F.Faccio – CERN/MIC Measured performance  Samples packaged and mounted on test boards, with different output capacitors (to test transient response)  10 samples measured  Quiescent current: 800  A at Vin=2.65V; 950  A at Vin=3.3V  Output noise (Cout=6.6  F), over full bandwidth: 170  V rms for I=0 170  V rms for I=0 530  V rms for I=250mA 530  V rms for I=250mA CRTREG1 Cout

Heidelberg LECC05F.Faccio – CERN/MIC Measured performance: line and load regulation  Measurements on 10 samples  Dropout at 300mA output current: average 160mV, maximum 235mV  Line regulation above Vin=2.8V, for I=300mA: average 1.7mV (0.09%/V), maximum 2.5mV (0.14%/V)  Load regulation from I=0 to I=300mA, for Vin=2.8V: average 14.2mV (0.0018%/mA), maximum 15.5mV (0.002%/mA) Line regulation Load regulation

Heidelberg LECC05F.Faccio – CERN/MIC Measured performance: protections  Over-Temperature OK: when regulator draws more than 1.8A at Vin=3.3V, it is disabled (test in temperature done by disabling Over-current protection and heating the regulator with large currents)  Over-Voltage OK: when Vin is above about 3.55 V, the regulator is disabled  Over-Current works but sets-in at current depending on Vin (up to 800mA). Origin understood and easy to correct.

Heidelberg LECC05F.Faccio – CERN/MIC Measured performance: line and load transients  Line transients: Transient of 500mV Vin At 100  A and 250mA For Cout =3.3  F and 6.6  F  Load transients: Transient from I=0 to 250mA Transient from I=0 to 250mA At Vin=2.65, 2.8 and 3.3V At Vin=2.65, 2.8 and 3.3V For Cout =1  F, 3.3  F and 6.6  F For Cout =1  F, 3.3  F and 6.6  F Vin=2.8V, Cout=6.6  F Time 10  S/div Output voltage 100mV/div 0 to 250mA 250mA to 0 I=250mA, Cout=6.6  F Output voltage 50mV/div Time 10  S/div Input voltage 200mV/div

Heidelberg LECC05F.Faccio – CERN/MIC Measured performance: PSRR  Power Supply Rejection measured injecting sine wave signal at different frequency at the input (50-100mV peak-peak)  Measurements for I=0 and 250mA, and for Cout=3.3  F and 6.6  F Vin=3V Cout=6.6  F Able to filter effectively at full load up to 100kHz (similar regulators cut at 1kHz typically)

Heidelberg LECC05F.Faccio – CERN/MIC Radiation performance (1)  Irradiation at IONISOS (Dagneux, F) with a 60 Co source; dose rate about 200 krad/h  Regulators under bias during irradiation: Vin=3V, I=0 (3 samples) and 250mA (3 samples)  TID levels achieved: 1.7 Mrad – 1 sample 1.7 Mrad – 1 sample 7.1 Mrad – 1 sample 7.1 Mrad – 1 sample 12.4 Mrad – 2 samples 12.4 Mrad – 2 samples 20 Mrad – 2 samples 20 Mrad – 2 samples  Measured performed for all samples at the end of irradiation, hence after annealing for hours at room T and under bias

Heidelberg LECC05F.Faccio – CERN/MIC Radiation performance (2)  Main effect: output voltage shifts with TID (max 110mV after 20Mrad). This is due to shift in bandgap voltage reference.  Line and load regulation do not change significantly Line regulation before (dots) and after 20Mrad (lines) I=0 to 300mA, step 50mA Load regulation before (dots) and after 20Mrad (lines) Vin=2.6V Vin=2.65V Vin=2.7V Vin=3V and 3.5V

Heidelberg LECC05F.Faccio – CERN/MIC Radiation performance summary  Output voltage shifts with TID  Over-voltage detection threshold shifts with TID  TID effects not dependent on load condition  Regulator tolerant to TID up to 20Mrad, probably more

Heidelberg LECC05F.Faccio – CERN/MIC Conclusion  CRTREG1, a compact LDO radiation-tolerant voltage regulator has been developed  Its performance is well comparable to commercial LDO regulators (dropout, line and load regulation, transient response, PSSR)  First prototype fully working, easy correction to be implemented for better stability of over-current protection  Radiation tolerance up to 20Mrad from 60 Co source has been demonstrated  The regulator is ready for production