Using the ADM2582E/87E, what current is available on Visoout for external loads? Our application has single terminated bus lines with termination of 120 ohms. What design considerations are there for connecting an external load to Visoout?
The typical output voltage of the integrated isoPower dc-to-dc isolated supply is 3.3 V. The isolated supply in the ADM2587E is capable of supplying a current of 55 mA when the junction temperature of the device is kept below 120°C. It is important to note that the current available on the VISOOUT pin is the total current available and includes the current required to supply the internal RS-485 circuitry.The ADM2587E can typically supply 15 mA externally on VISOOUT when the driver is switching at 500 kbps loaded with 54 Ω, while the junction temperature of the part is less than 120°C.
Typical Maximum External Current Available on VISOOUT
External Load Current (mA)
Double terminated bus with RT = 110 Ω
Single terminated bus
The ADM2582E typically has no current available externally on VISOOUT.
When external current is drawn from the VISOOUT pin, there is an increased risk of generating radiated emissions due to the high frequency switching elements used in the isoPower dc to-dc converter. Special care must be taken during PCB layout to meet emissions standards. See Application Note AN-0971, Control of Radiated Emissions with isoPower Devices, for details on board layout considerations.
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