Current sensing; output and supply current

Document created by analog-archivist Employee on Feb 23, 2016
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We will use the ADL5565 for amplifying the signal of a DAC and driving towards
two coax connectors. Source termination is 2 x 50 ohms, the connected load
another 100 ohms. Input and output of the amplifier is DC coupled. My concern
is now to kill the ADL5565 e.g. in case of shorting respectively missing
termination at the other end of the cable. 2 Vpeak (SE) / 50 Ohm = 40 mA to
GND. Adding the common mode voltage makes the thing even worse. Since the
absolute maximum rating is 30 mA I try to find a possibility to
observe the case of an exceeding output current.

1. Can I assume to detect such a situation by adding a high-side current
sensing at the supply rail?
2. Is supply current stable at its ~80 mA or will the load influence the
consumption?
3. Will an output current of 50 mA damage the device?
4. How can I ensure to not exceed the ADL5565s maximum output current of
+/-30mA ?

 

1. High-side current sensing is an appropriate method to determine shorts as
well as continuous current monitoring for low currents, usually <100A.
Regarding high-side current sensing kindly refer to the technical article from
Analog Dialogue:

http://www.analog.com/library/analogdialogue/archives/42-01/high_side_current_se
nsing.pdf.

2. Parameters, like the quiescent current, in the datasheet are determined
under the conditions mentioned in the Specifications section of the
www.analog.com/ADL5565  datasheet. For the determination of the parameters the
load is fixed at R_L = 200Ohm and C_L = 1pF, both differential. For differing
conditions, like a different applied load, the specified parameters can alter.

Kindly compare for example the temperature dependency of the part in Figure 29
on page 15 of the datasheet. Figure 29 gives an impression how the supply
current typically changes under varying temperature conditions.

3. The maximum output current for the ADL5565 amounts to +/-30 mA, as the
“absolute maximum ratings” in the specification section of the data sheet
indicates. Using 50 mA output current may cause damage to the part, see section
“Absolute Maximum Rating” on page 9 in the datasheet. Stresses above those
listed under Absolute Maximum Ratings may cause permanent damage to the device.
This is a stress rating only; functional operation of the device at these or
any other conditions above those indicated in the operational section of this
specification is not implied. Exposure to absolute maximum rating conditions
for extended periods may affect device reliability.

4. In order to give recommendations can you kindly provide some more detailed
information as mentioned below:
a. Schematic? b. What is your frequency range? c. What is your maximum output
current?

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