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A radiation-tolerant LDO
voltage regulator for HEP
applications
F.Faccio, P.Moreira, A.Marchioro, S.Velitchko
CERN
Outline

Motivation
 Specifications
 Implementation
 Measured performance
 Radiation performance
 Conclusion
Heidelberg LECC05
F.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 100150mV
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!
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F.Faccio – CERN/MIC
Specifications
Min
Typ
Output V (V)
Input V (V)
Output I (mA)
Max
Comment
2.5
Fixed in this version
2.65
2.7
3.5
0
250
300
Dropout V (mV)
150
Quiescent I (mA)
At 300mA current
1
Over-V prot. (V)
3.5
Protects regulator itself
Over-I prot. (mA)
400
600 Switch to current regulation
Over-T prot. (oC)
150
170
Disable in/out
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yes
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Possible to disable, output
flag
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 6.6mF) 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 0.25mm CMOS technology using
radiation-tolerant layout techniques
Heidelberg LECC05
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Implementation (2)
Functional block diagram
Vin
Vout
Switches
for disable
R1
Over-I
monitor
Over-V
monitor
off
Error
amplifier
R2
Over-T
monitor
Bandgap
Disable in
Disable flag
Heidelberg LECC05
F.Faccio – CERN/MIC
Gnd
Implementation (3)
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

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 LECC05
F.Faccio – CERN/MIC
Measured performance


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Samples packaged and
mounted on test boards, with
different output capacitors (to
test transient response)
10 samples measured
Quiescent current: 800mA at
Vin=2.65V; 950mA at
Vin=3.3V
Output noise (Cout=6.6mF),
over full bandwidth:


170mV rms for I=0
530mV rms for I=250mA
Heidelberg LECC05
F.Faccio – CERN/MIC
CRTREG1
Cout
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
2.6
2.56
2.55
2.54
2.5
Iout=0A
Vout (V)
Vout (V)
Load regulation
2.58
Iout=0.05A
2.45
Iout=0.1A
2.52
Vin=2.6V
2.5
Vin=2.65V
Iout=0.15A
2.4
2.48
Iout=0.2A
Vin=3.0V
Iout=0.25A
2.35
Vin=2.7V
2.46
Iout=0.3A
2.3
Vin=3.5V
2.44
2.5
2.7
2.9
3.1
3.3
3.5
0
Vin (V)
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0.05
0.1
0.15
0.2
Output current (A)
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0.25
0.3
0.35
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 LECC05
F.Faccio – CERN/MIC
Measured performance: line and
load transients
Line transients:


Input voltage Output voltage
200mV/div 50mV/div

Load transients:

Transient of 500mV Vin
At 100mA and 250mA
For Cout =3.3mF and
6.6mF
I=250mA, Cout=6.6mF



Output voltage 100mV/div

Vin=2.8V, Cout=6.6mF
250mA to 0
0 to 250mA
Time 10mS/div
Heidelberg LECC05
Transient from I=0 to 250mA
At Vin=2.65, 2.8 and 3.3V
For Cout =1mF, 3.3mF and
6.6mF
Time 10mS/div
F.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=3.3mF and
6.6mF
0
-10
Vin=3V
Cout=6.6mF
PSSR (dB)
-20
Load=0A
Load=250mA
-30
Able to filter
effectively at full
load up to 100kHz
(similar regulators
cut at 1kHz
typically)
-40
-50
-60
-70
-80
-90
1.E+00
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1.E+02
1.E+04
1.E+06
Frequency (Hz)
F.Faccio – CERN/MIC
1.E+08
Radiation performance (1)
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Irradiation at IONISOS (Dagneux, F) with a 60Co
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:
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1.7 Mrad – 1 sample
7.1 Mrad – 1 sample
12.4 Mrad – 2 samples
20 Mrad – 2 samples
Measured performed for all samples at the end of
irradiation, hence after annealing for 57-114 hours at
room T and under bias
Heidelberg LECC05
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Radiation performance (2)


2.7
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)
2.7
Vin=3V and 3.5V
2.65
2.65
I=0 to 300mA, step 50mA
2.6
Vin=2.7V
2.6
2.55
Vout (V)
Vout (V)
Load regulation before (dots)
and after 20Mrad (lines)
2.5
2.45
2.55
Vin=2.65V
2.5
2.4
Vin=2.6V
2.45
2.35
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
3.3
3.4
3.5
0
Vin (V)
Heidelberg LECC05
0.05
0.1
0.15
Output current (A)
F.Faccio – CERN/MIC
0.2
0.25
0.3
Radiation performance summary
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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
1.7Mrd+144hours
load=250mA
pre-rad
after rad
Output voltage (V)
Dropout V (mV)
Line regulation (mV)
I=100mA
I=300mA
Load regulation (mV)
Vin=2.75V
Vin=2.8V
OverV threshold (V)
Vbandgap (V)
V2V5 (V)
Heidelberg LECC05
7.12Mrd+117hours
load=0
pre-rad
after rad
12.4Mrd+96hours
load=0
pre-rad
after rad
20Mrd+57hours
load=250mA
pre-rad
after rad
2.53
234
2.54
138
2.55
186
2.59
134
2.55
135
2.63
135
2.54
135
2.65
137
0.7
1.2
0.8
0.9
1.2
1
1.7
0.6
0.2
2.3
0.9
0.9
0.7
2.4
1.4
2
18.3
14.8
3.61
14.1
13.7
3.57
1.18
2.35
15.7
14.2
3.6
14.9
13.8
3.62
1.196
2.38
14.6
14.2
3.57
33
15.1
3.67
1.214
2.42
14.3
13.6
3.55
53.2
16.5
3.69
1.223
2.43
F.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 60Co source
has been demonstrated
 The regulator is ready for production
Heidelberg LECC05
F.Faccio – CERN/MIC