Noty AN141f Linear Technology

Application Note 141

October 2013

Risk Assessment Advice for High Reliability Amplifiers

Tim Regan and James Mahoney

Introduction

In long life, high reliability systems, supplied power is
provided only to essential circuitry. As a result many of
the unpowered circuits may have voltages applied to in

­puts and outputs without proper supply biasing. As part
of any diligent system safety risk assessment, a question
often arises; will the unpowered components be damaged,

degraded, or impair circuit performance under these
abnormal operating conditions?

The purpose of this article is to provide advice for what
lies within the pins of several common amplifiers used in
these applications. Most of the amplifiers of interest are the
radiation hard amplifiers so indicated with a device prefix
of RH. Another amplifier, the LT6016, is particularly robust
with over, under and reversed polarity voltage conditions
and is included for reference.

With no power applied to the amplifier, forcing a voltage
between two pins will cause a current to flow. The mag­nitude of this current differs from pin to pin and device to

ice. A curve tracer is used to show the current vs voltage

dev
characteristic when overdriving specific pin combinations.

Referencing these curve trace plots will provide an indi­cation of the magnitude of current flow for a particular
voltage applied and also any clamp voltage at the device
pin. From these it is hoped that an educated assessment
of the risk of damage can be made.

Another plot shows what to expect under a reverse polarity
supply connection.

A plot with voltage applied between the two inputs is also
provided. For amplifiers which contain protection diodes
between the inputs this plot is accurate. For amplifiers
which do not contain such diodes this plot can be mis

­leading since the supply voltage pins are open circuited.
The internal transistor action with power supplied can be
quite different. Devices having different characteristics
with power supplied are noted.

The usefulness of these plots can be shown through an
example. In Figure 1 an RH/LT1013 op amp is powered off
with its supply pins at circuit ground while other circuitry
is active and presents ±10V potentials through resistors
to the –IN pin and the OUTPUT pin.

10k

15V

INPUT

10V

10k

10k

–

+

–15V

10k

–

+

+

–

+

–

LT1013

LT1013

–10V

2k

2k

OUTPUT

AN141 F01

How to Interpret This Information?

For each amplifier a set of curve trace plots is provided.
These

plots indicate the expected current flow should the
inputs and output be connected to voltages outside the
supply rails.

Also shown is a plot of a normal supply connection voltage
sweep which indicates the amplifier’s start-up characteris­tic. A note added to this plot states at what point to expect
a supply overvoltage condition where the supply current
begins to increase rapidly.

Figure 1. Example of Unpowered Redundant Circuitry

The input condition will try to pull the –IN pin positive.

–

Pulling this input above the V

supply rail is normal circuit

operation for the RH/LT1013 so not a problem, but pull-

+

ing it above the V

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.

supply rail is abnormal and needs to

an141f

AN141-1

Application Note 141

be checked. Refer to the plot for the RH/LT1013 showing

+

the –IN to V

characteristic, as shown in Figure 2. With
an input resistor of 10k the maximum current flow will be
1mA. At 1mA the –IN pin will pull up to near +1V. This plot
shows that this input pin could be pulled to 50V above

+

with 30mA of input current without damage. The input

V
biasing condition of this example is likely to be quite safe.

50

LT1013 –IN TO V

45

40

I

35

+

V

30

–

25

5mA/DIV

20

15

10

5

0

0

Figure 2. RH/LT1013 –IN Above V+ Plot

+

+

V

+

–

25 4515 35

5V/DIV

5020 405 10 30

AN141 F02

The output is being pulled negative through 4k of resistance.

–

Checking the OUT to V

plot for this amplifier, Figure 3,

shows that the output will clamp at a diode drop below

0

5

10

15

20

25

5mA/DIV

30

35

40

45

50

–2

LT1013 OUT TO V

+

–

V

–

I

_

–

V

+

–1 –0.2–1.4 –0.6

200mV/DIV

0–1.2 –0.4–1.8 –1.6 –0.8

AN141 F03

–

rail, approximately –0.7V with 2.5mA of current

the V
flow. This internal diode is fairly large and as shown in the
plot can safely conduct 10’s of mAs. This condition will
not likely cause any damage to the unpowered amplifier.

Another consequence of this condition however is loading
of the powered amplifier caused by the output clamping
of the unpowered amplifier. In this example the powered
amplifier must be able to sink the 2.5mA of current to
output the –10V level expected. If the powered amplifier
is from another RH/LT1013 package, it is able to sink this
much current so operation should be as expected. Other
lower power amplifiers may not have the output current
capability and the circuit output will be in error caused
by the loading interaction from the unpowered amplifier.

Use of these plots can provide a good starting point for
the evaluation of the risk of circuit damage and/or potential
erroneous operation of systems subjected to abnormal
supply connections. To help locate the plots for a particular
amplifier this index is provided:

INDEX

Amplifier Equivalent Tested Device Page

LT6016 LT6016 4

OP07 5

RH07
RH1013
RH1014
RH1028
RH1078
RH108
RH1056
RH118
RH1128
RH1498
RH1499
RH1814
RH27
RH37
RH6200

LT1013 6
LT1014 7
LT1028 8
LT1078 9

LM108 10

LT1056 11

LM118 12

LT1028 8
LT1498 13
LT1498 13

LT1814 14
LT1007 15
LT1007 15

LT6200 16

Figure 3. RH/LT1013 OUT Below V

AN141-2

–

Plot

an141f

Application Note 141

Tips and Disclaimers

1. These measurements were taken on typical production
devices.

2. The majority of RH devices are electrically equivalent
to the commercial LT version of the same device. Most
of these measurements were taken on LT devices. The
effects of radiation dosing is not addressed in this study.

3. This information is to be considered as typical room
temperature performance. For characterization tem

perature behavior or radiation effects, the specific LT
or RH die is highly recommended to obtain optimal
data. No guarantee of device compliance to these
measurements is to be assumed. Absolute Maximum
Ratings apply. Check data sheet for more information.

4. The intent of these measurements is solely to provide
advice for what to expect under abnormal biasing condi
tions.

Most amplifiers contain built-in protection circuitry at

5.
input and output pins, primarily for ESD protection. This
circuitry is designed to redirect potentially destructive
current from sensitive transistor structures.

-

-

6. A current of 10mA or less into or out of any pin of
these amplifiers is generally considered safe and non­destructive short term or long term. Applied voltages
less than the maximum rated supply voltage of the
amplifier will be less likely to cause adverse transistor
voltage breakdown effects.

7. A curve tracer sweeps the applied voltage for some
measure of repetitive application. Long term effects
or degradation from long term continuous or repetitive
overvoltage conditions is not part of this study. If the
current is flowing primarily through a simple protection
diode it can generally be considered safe for the long
term.

8. These tests were performed with voltage applied only
to the indicated pins. Unless otherwise indicated the
power supply pins of the amplifiers are open circuited.

9. After the curve trace testing, these units were verified
to still have normal functionality in a typical application
circuit on a lab bench setup at room temperature. They
were not fully retested for all data sheet specifications
on an automated production test system.

an141f

AN141-3

Application Note 141

AN141 G02

AN141 G08

Amplifier Type: LT6016 Similar Devices: LT6015, LT6016, LT6017 Tested Device: LT6016

200

180

160

140

120

100

20µA/DIV

80

60

40

20

0

0

0

0.5

1.0

1.5

2.0

2.5

0.5mA/DIV

3.0

3.5

4.0

4.5

5.0
–5

LT6016 +IN TO V

I

+

+

–

V

–

LT6016 +IN TO V

+

I

–

–

V

+

+

+

V

50 9030 70

10V/DIV

+IN to V

–

–

V

–2.5 –0.5–3.5 –1.5

0.5V/DIV

+IN to V

200

LT6016 –IN TO V

180

160

140

120

100

20µA/DIV

10040 8010 20 60

AN141 G01

I

+

V

–

80

60

40

20

0

0

+

0

LT6016 –IN TO V

0.5

AN141 G04

1.0

1.5

2.0

2.5

0.5mA/DIV

3.0

3.5

4.0

4.5

03 –1–4.5 –4 2

5.0

I

–

V

+

–5

–

+

–

+

–

+

+

V

50 9030 70

10V/DIV

–IN to V

–

–

V

–2.5 –0.5–3.5 –1.5

0.5mV/DIV

–IN to V

10040 8010 20 60

+

03 –1–4.5 –4 2

AN141 G05

–

200

180

160

140

120

100

20µA/DIV

80

60

40

20

0

0

0

2

4

6

8

10

2mA/DIV

12

14

16

18

20

–1

LT6016 OUT TO V

+

V

+

–

OUT

OUT to V

+

I

+

V

–

50 9030 70

10V/DIV

LT6016 OUT TO V

+

–

–0.5 –0.1–0.7 –0.3

100mV/DIV

OUT to V

10040 8010 20 60

AN141 G03

+

–

I

–

V

–

V

+

0–0.6 –0.2–0.9 –0.8 –0.4

–

AN141 G06

2000

LT6016 V+ TO V

1800

NORMAL POWER SUPPLY

1600

1400

1200

1000

200µA/DIV

800

600

400

200

I

+

+

V

–

–

SUPPLY VOLTAGE BREAKDOWN
BEGINS AT 72V. AT BREAKDOWN
I

0

0

SUPPLY

V+ to V– (Normal Supply) V– to V+ (Reverse Supply) +IN to –IN (Differential Input)

AN141-4

–

+

V

–

V

INCREASES TO 1200µA.

25 4515 35

5V/DIV

AN141 G07

5.0
LT6016 V– TO V

4.5

REVERSE POWER APPLIED

4.0

3.5

3.0

2.5

0.5mA/DIV

2.0

1.5

1.0

0.5

0

5020 405 10 30

0

+

+

V

+

–

–

V

I

+

V

–

50 9030 70

10V/DIV

10040 8010 20 60

1000

800

600

400

200

0

200µA/DIV

–200

–400

–600

–800

–1000

–50

LT6016 +IN TO –IN

I

+

–

V

+

–

DIFFERENTIAL INPUT

+

–

DIFFERENT CHARACTERISTIC
WITH POWER SUPPLIED

0 40–20 20

10V/DIV

AN141 G09

an141f

50–10 30–40 –30 10

Application Note 141

AN141 G18

AN141 G17

Amplifier Type: RH07 Similar Devices: OP07 Tested Device: OP07

50

45

40

35

30

25

5mA/DIV

20

15

10

5

0

0

0

5

10

15

20

25

5mA/DIV

30

35

40

45

50

–20

OP-07 +IN TO V

I

+

+

–

V

–

OP-07 +IN TO V

+

I

–

–

V

+

+

+

V

10 186 14

2V/DIV

+IN to V

–

–

V

–10 –2–14 –6

2V/DIV

+IN to V

50

OP-07 –IN TO V

45

40

I

35

+

30

V

25

5mA/DIV

208 162 4 12

AN141 G10

–

20

15

10

5

0

0

+

0

OP-07 –IN TO V

5

10

15

–

20

V

25

5mA/DIV

0–12 –4–18 –16 –8

AN141 G13

+

30

35

40

45

50

–20

–

+

+

V

+

–

10 186 14

2V/DIV

–IN to V

–

+

208 162 4 12

AN141 G11

+

I

–

–

V

–10 –2–14 –6

2V/DIV

–IN to V

0–12 –4–18 –16 –8

AN141 G14

–

100

90

80

70

60

50

10mA/DIV

40

30

20

10

0

0

0

5

10

15

20

25

5mA/DIV

30

35

40

45

50

–2

OP-07 OUT TO V

+

V

+

–

OUT

+

I

+

V

–

1 1.80.6 1.4

200mV/DIV

OUT to V

OP-07 OUT TO V

+

–

–1 –0.2–1.4 –0.6

200mV/DIV

OUT to V

20.8 1.60.2 0.4 1.2

AN141 G12

+

–

I

–

V

–

V

+

0–1.2 –0.4–1.8 –1.6 –0.8

AN141 G15

–

20

OP-07 V+ TO V

18

NORMAL POWER SUPPLY

16

14

12

10

2mA/DIV

I

+

V

–

8

6

4

2

0

0

V+ to V– (Normal Supply) V– to V+ (Reverse Supply) +IN to –IN (Differential Input)

–

+

V

+

–

–

V

SUPPLY VOLTAGE BREAKDOWN
BEGINS AT 48V. AT BREAKDOWN

INCREASES TO 9mA.

I

SUPPLY

25 4515 35

5V/DIV

AN141 G16

50

OP-07 V– TO V

45

REVERSE POWER APPLIED

40

35

30

25

5mA/DIV

20

15

10

05

0

5020 405 10 30

0

+

+

V

+

–

–

V

I

+

V

–

0.5 0.90.3 0.7

100mV/DIV

10.4 0.80.1 0.2 0.6

10

8

6

4

2

0

2mA/DIV

–2

–4

–6

–8

–10

–5

I

+

+

–

V

+

–

–

OP-07 +IN TO –IN
DIFFERENTIAL INPUT

0 4–2 2

1V/DIV

5–1 3–4 –3 1

an141f

AN141-5