problem with adm483, often burn!!!

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ADM483: RS-485/RS-422 Transceivers

I have an application that I use adm483 for serial communication beetween two devices.
The problem is that very often the adm483 burn and I dont understand the reason.

Both devices have common source 24V AC, and there is rectifier and switching power supply from DC 24V to 5V.

I watch carefully and I saw that the most of times that the adm483 is burned, is when I switch off the one device (cause I want remove mega8 for program update) as the second device is still powered.

Why adm483 is burned? I cant understand, any advice?

Learn as long as you live

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Think i'd need to see the schematic to comment.

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This is the schematic for mega8 and adm483.

Both devices are exactly the same, just the software changes.

Temporarily I dont have put any terminal resistor in communication line, cause I still not decide what resistor to use.

Must be noted that most is burned the adm483 in device that I switch off. !! strange !! I think something wrong with the communication line (pins 6,7).

Any suggestion?

Attachment(s): 

Learn as long as you live

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Either loading the outputs or static protection diodes are conducting or exceeding MAX VCC. The part gets pretty hot before it limits load current overload..

Have you put a DVM on your VCC to measure it? A SMPS can swing above the set regulation when it powers up, etc. Good idea to use a zener to clamp to say 5.2 or 5.6 volts.

Check the PCB for unintended shorts or bridges?

Are both the AVR and ADM483 on the same pcb to be clear about the problem?

The ADM483 contains thermal shutdown circuitry that protects the part from excessive power dissipation during fault conditions. Shorting the driver outputs to a low impedance source can result in high driver currents. The thermal sensing circuitry detects the increase in die temp-erature and disables the driver outputs. The thermal sensing circuitry is designed to disable the driver outputs when a die temperature of 150°C is reached. As the device cools, the drivers are re-enabled at 140°C.

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kzdev wrote:
ADM483: RS-485/RS-422 Transceivers

I have an application that I use adm483 for serial communication beetween two devices.
The problem is that very often the adm483 burn and I dont understand the reason.

Both devices have common source 24V AC, and there is rectifier and switching power supply from DC 24V to 5V.

I watch carefully and I saw that the most of times that the adm483 is burned, is when I switch off the one device (cause I want remove mega8 for program update) as the second device is still powered.

Why adm483 is burned? I cant understand, any advice?

Interconnect GND.

HM

HM

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I dare say there is a sneak path between the boards. The ADM483 style chips don't like 24v on their bus and will most likely go up in smoke as described.

Analyse your circuit to identify the sneak path. Possible solutions are:
1. remove the sneak path
2. add protection (polyfuse/transzorb diode)
3 use a linear tech LTC1785 transceiver.

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One thing is that these interface chips DO NOT like external signal connected when they do not have power.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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thanx for your responses,

Before in other projects I din't have problem like this.

I will check again carefully my PCB, and I will follow your suggestions. I hope to find something.

Learn as long as you live