ADA4807-2ACPZ-R2 datasheet(25/33 Pages) AD

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Data Sheet

ADA4807-1/ADA4807-2/ADA4807-4

Rev. B | Page 25 of 33

DISABLE CIRCUITRY

When the DISABLE pin is an option, a pull-up resistor is required

if the logic leakage currents exceed 300 nA. For a 10 V supply,

pulling the DISABLE pin to below 6.3 V turns the ADA4807-1/

ADA4807-2 off, which reduces the supply current to 2.4 µA.

Conversely, pulling the DISABLE pin voltage to above 6.6 V

enables the ADA4807-1/ADA4807-2 with a quiescent current of

1 mA. When the ADA4807-1/ADA4807-2 device is disabled, its

output enters a high impedance state. Figure 64 and Table 10

show the DISABLE functionality over the complete supply range.

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

3.8

4.0

POWER SUPPLY, VS (V)

VTH

VON = VTH +150mV

VOFF = VTH –150mV

Figure 64. DISABLE Trigger Voltage

Table 10. Threshold Voltages for Disabled and Enabled Modes

Mode

+3 V

+5 V

+10 V

±5 V

+7 V/−2 V

Enabled

1.35 V

1.6 V

6.6 V

1.6 V

3.6 V

Disabled

1.05 V

1.3 V

6.3 V

1.3 V

3.3 V

The output impedance decreases as the frequency increases. When

disabled, a forward isolation of 120 dB is achieved at 100 kHz (see

Figure 22). ESD clamps protect the DISABLE pin, as shown in

Figure 65. Voltages beyond the power supplies cause these diodes

to conduct. To avoid excessive current in the ESD diodes, ensure

that the voltage to the DISABLE pin is not 0.7 V greater than the

positive supply or that it is not 0.7 V less than the negative supply.

If an overvoltage condition is expected, limit the input current to

less than 10 mA with a series resistor.

INPUT PROTECTION

The ADA4807-1/ADA4807-2/ADA4807-4 are fully protected

from ESD events, withstanding human body model ESD events

of ±3 kV and charged device model events of ±1.25 kV with no

measured performance degradation. The precision input is

protected with an ESD network between the power supplies and

diode clamps across the input device pair, as shown in Figure 65.

For differential voltages above approximately 1.2 V at room

temperature and 0.8 V at 125°C, the diode clamps begin to

conduct. Too much current can cause damage due to excessive

heating. If large differential voltages must be sustained across the

input terminals, it is recommended that the current through the

input clamps be limited to less than 10 mA. Series input resistors

sized appropriately for the expected differential overvoltage

provide the needed protection.

+INx

ESD

–VS

+VS

BIAS

TO THE REST OF THE AMPLIFIER

–INx

ESD

NOTES

1. THE ±INx PINS ARE ±IN ON THE ADA4807-1,

±IN1 AND ±IN2 ON THE ADA4807-2,

AND ±IN1 TO ±IN4 ON THE ADA4807-4.

Figure 65. Input Stage and Protection Diodes

NOISE CONSIDERATIONS

Figure 66 illustrates the primary noise contributors for the typical

gain configurations. The total output noise (VN_OUT) is the root

sum square of all the noise contributions.

iep

ien

+ vout_en –

ven

4kT × RS

VN _ RS =

4kT × RG

VN _ RG =

4kT × RF

VN _ RF =

Figure 66. Noise Sources in Typical Gain Configurations

Source resistance noise, amplifier input voltage noise, and the

voltage noise from the amplifier input current noise (IN+ × RS)

are all subject to the noise gain term (1 + RF/RG).

Calculate the output noise spectral density using the following

equation:

[

]

OUT

kTR

kTRs

kTR

−

























where:

k is Boltzmann’s constant.

T is the absolute temperature in degrees Kelvin.

RF and RG are the feedback network resistances, as shown in

Figure 66.

RS is the source resistance, as shown in Figure 66.

IN+ and IN− represent the amplifier input current noise spectral

density in pA/√Hz.

VN is the amplifier input voltage noise spectral density in nV/√Hz.

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