AD713: Output short circuit specifications

Q 

I have got some questions about the output short circuit capability of
AD713JR-16.
In the datasheet (Rev. C) it is not clear said if the outputs are short circuit
protected.

The absolute maximum ratings say, output short circuit duration for one
amplifier is indefinite.
1. Does this mean, there is no time limit, if only one output is shorted to
ground?
2. What happens, if all four outputs are shorted to ground at the same time? Is
the device destroyed, does it depend on the thermal characteristics of the SOIC
package?
3. Is there a thermal overload protection or thermal shutdown?

In the specifications the output current at short circuit condition is typical
25mA.
4. Is this the typical value of the short circuit current limit?
5. What is the (aproximate) maximum value of the short circuit current limit?

 

A 

1. We only guarantee indefinite short circuit capability if one output is
shorted. Permanently shorting 2 or more outputs may damage or destroy the AD713.

2. If all four outputs are shorted to ground , then the device will dissipate
power P = 4 x 25mA x Vs  = 100mA x Vs = 100mA x 15V = 1.5W. This will cause a
temperature rise of around 150 degrees above ambient, if the device has no heat
sink attached, which will almost certainly destroy the device at temperatures
above 0degC.

3. Figure 8 of the datasheet shows how the short circuit current limit varies
with temperature. It automatically reduces the short circuit current limit when
the junction temperature rises, as shown.

4. & 5. See figure 3 on the datasheet. At +/-15V supplies and high output
impedance (>2k) the voltage swing is more or less constant with load
resistance. As one moves from right to left, in the direction of decreasing the
load resistance, the curve becomes an exponential shape. This corresponds to a
region of CONSTANT CURRENT. If the x axis was linear then it would be a
straight line, but since the x-axis is logarithmic, the constant current as R
decreases is an exponential. The constant current is around 25mA, but this can
vary with temperature, supply voltage and each device will have a different
value. It's not possible to guarantee a maximum short circuit current limit,
since only a typical is given in the datasheet.