AD8510/AD8512/AD8513

Rev. E | Page 13 of 20

GENERAL APPLICATION INFORMATION

INPUT OVERVOLTAGE PROTECTION

The AD8510/AD8512/AD8513 have internal protective

circuitry that allows voltages as high as 0.7 V beyond the

supplies to be applied at the input of either terminal without

causing damage. For higher input voltages, a series resistor is

necessary to limit the input current. The resistor value can be

determined from the formula

mA

R

V

V

S

S

IN

5

≤

−

With a very low offset current of <0.5 nA up to 125°C, higher

resistor values can be used in series with the inputs. A 5 kΩ

resistor will protect the inputs to voltages as high as 25 V

beyond the supplies and will add less than 10 µV to the offset.

OUTPUT PHASE REVERSAL

Phase reversal is a change of polarity in the transfer function of

the amplifier. This can occur when the voltage applied at the

input of an amplifier exceeds the maximum common-mode

voltage.

Phase reversal can cause permanent damage to the device and

may result in system lockups. The AD8510/AD8512/AD8513 do

not exhibit phase reversal when input voltages are beyond the

supplies.

TIME (20

µs/DIV)

Figure 41. No Phase Reversal

THD + NOISE

The AD8510/AD8512/AD8513 have low total harmonic distor-

tion and excellent gain linearity, making these amplifiers a great

choice for precision circuits with high closed-loop gain, and for

audio application circuits. Figure 42 shows that the AD8510/

AD8512/AD8513 have approximately 0.0005% of total distor-

tion when configured in positive unity gain (the worst case) and

driving a 100 kΩ load.

FREQUENCY (Hz)

0.01

0.001

0.0001

20

100

1k

20k

BW = 22kHz

Figure 42. THD + N vs. Frequency

TOTAL NOISE INCLUDING SOURCE RESISTORS

The low input current noise and input bias current of the

AD8510/AD8512/AD8513 make them the ideal amplifiers for

circuits with substantial input source resistance. Input offset

voltage increases by less than 15 nV per 500 Ω of source

resistance at room temperature. The total noise density of the

circuit is

(

)

S

S

n

n

nTOTAL

kTR

R

i

e

e

4

2

2

+

+

=

where:

T is the ambient temperature in Kelvin (T = 273 + °C).

The current noise of the AD8510/AD8512/AD8513 is so low

that its total density does not become a significant term unless

applications.

The total equivalent rms noise over a specific bandwidth is

expressed as

BW

e

e

nTOTAL

where

BW is the bandwidth in Hertz.

Note that the above analysis is valid for frequencies larger than

150 Hz and assumes flat noise above 10 kHz. For lower frequen-

cies, flicker noise (1/f) must be considered.