AD8628 datasheet(23/29 Pages) AD

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Data Sheet

ADA4523-1

Rev. 0 | Page 23 of 29

ELECTRICAL OVERSTRESS AND INPUT PROTECTION

Do not exceed the absolute maximum ratings. Avoid driving the

input and output pins beyond the rails, especially at supply

voltages approaching 40 V. The inputs of the ADA4523-1 are

internally protected by ESD diodes and an ESD clamp (see

Figure 64). When the inputs are driven above and/or below the

supply rail, the inputs draw substantial input currents, as shown

in Figure 71.

–20

2.0

INPUT VOLTAGE BEYOND SUPPLY (V)

–15

–10

–5

0.4

0.8

1.2

1.6

+125°C

+25°C

–40°C

FORWARD BIASING

ESD PROTECTION DIODE

BETWEEN INPUT AND V+

FORWARD BIASING

ESD PROTECTION DIODE

BETWEEN INPUT AND V–

Figure 71. Input Current vs. Input Voltage Beyond Supply, ESD Protection

Diode Forward Bias Voltage

If a large differential input voltage is imposed between +IN and

−IN, the resulting input bias current is as shown in Figure 72.

Note that the +IN and −IN bias currents are asymmetrical due

to the input ESD clamp structure of the ADA4523-1. Some

additional current is sourced from the supply when a large

input voltage separates +IN from −IN, and this current then

exits the device through −IN.

–20

–2.0

2.0

DIFFERENTIAL INPUT VOLTAGE (V)

–16

–12

–8

–4

–1.6

–1.2

–0.8

–0.4

0.4

0.8

1.2

1.6

+IN –40°C

–IN –40°C

+IN +25°C

–IN +25°C

+IN +125°C

–IN +125°C

MEASUREMENT IS CURRENT LIMITED TO 20mA

VS = ±15V

VCM = 0V

Figure 72. Input Current vs. Differential Input Voltage for +IN and –IN and

Various Temperatures

If overvoltage conditions cannot be prevented, a resistor in

series (RIN) with the threatened pin can limit fault current,

IOVERLOAD, to below the absolute maximum rating and reduce

the possibility of device damage (see Figure 73).

RIN

1kΩ

ADA4523-1

VIN

V+

V–

OUT

IOVERLOAD

RIN LIMITS IOVERLOAD TO <10mA

FOR VIN < 10V OUTSIDE OF THE SUPPLY RAILS.

Figure 73. Using a Resistor to Limit the Input Current

Keep the current-limit resistance low enough to not add noise

and error voltages from interaction with the input bias currents.

Resistances ≤1 kΩ do not significantly impact noise or precision.

See Figure 71 and Figure 72 for the characteristics of the internal

ESD diodes to help determine the appropriate value of the resistor.

In harsh environments, reliability can be enhanced further with

protection circuitry. The circuit shown in Figure 74 uses low

leakage diodes (Nexperia BAV199) to protect the input. R2

protects the external diodes, and R1 limits the current that may

flow through the internal diodes. In this circuit, R1 can be small

because the applied voltage is already reduced by the external

protection diodes.

ADA4523-1

VIN

D1A

BAV199

D1B

BAV199

V+

V–

Figure 74. Input Protection Circuit Using External Diodes

In high temperature applications where the leakage currents of

the internal ESD diodes dominate the input bias current, the

circuit can benefit from adding an input bias cancellation

resistor in the feedback path.

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