SN65HVD3082E: SN65HVD3082E total power consumption for 256 loads

MIKHAIL SALOV

Good day Colleagues,

Could you tell me about a total power consumption of the SN65HVD3082E for 100kBit/sec data rate and 256 loads? Termination is 60 Ohm.

Am I correct the total current will be 35 mA + 8 mA = 43mA (figures 5 and 2 from the datasheet)?

Datasheet also says, the output current can be up to 60mA, but I can't understand for what condition 60mA can flow to the output?

Customer has only 85mA of the current to supply the transceiver for RS-485 and worries it will be not enough.

Thank you, Mike

over 9 years ago

0 Matt Mendez over 9 years ago

TI__Intellectual 2885 points

Hi Mike,

You are correct about the total current. The datasheet does say the max output current can go up to 60 mA, but this is for all the 308XE parts. As can be see in Figures 3 and 4, parts 3085E and 3088E have higher signal rates, and thus consume more current, matching the spec of 60 mA.

The total power consumption of the system will be P = (43 mA)(5.5 V) = 0.2365 W. this is only for one part, but I assume you will only have one part active at a time in your network.

If your customer has 85 mA to supply, you have more than enough to supply the transceiver.

0 MIKHAIL SALOV over 9 years ago in reply to Matt Mendez

TI__Expert 7640 points

Thank you, Matt,

Now it's absolutely clear,

Mike

0 MIKHAIL SALOV over 9 years ago in reply to MIKHAIL SALOV

TI__Expert 7640 points

Matt,

Could you tell me, have I add the total current for all receivers on the line (256 nodes)?

I mean if you look at table 6.6 in the datasheet, you'll see Bus input current 0.125mA max.

So means for 256 nodes it can be 32mA. So the power supply has to have the ability to supply 43mA + 32mA (bus input current) = 75mA

I am correct?

Thank you, Mike

0 Matt Mendez over 9 years ago in reply to MIKHAIL SALOV

TI__Intellectual 2885 points

Hi Mike,

Yes, that is technically correct, but that is under the absolute worst test conditions, so you will likely not see 75 mA.

0 MIKHAIL SALOV over 9 years ago in reply to Matt Mendez

TI__Expert 7640 points

Good day Matt,

Thank you!

Could you also tell me about short circuit?

Datasheet says Short-circuit output current is 250mA.

Is it internal current limit at 250mA level? Or package dissipation limitation?

What is the behavior if the short circuit happens?

Thank you, Mike

0 Matt Mendez over 9 years ago in reply to MIKHAIL SALOV

TI__Intellectual 2885 points

Hi Mike,

the Short-circuit output current is an internal limit, looking at page 15, Section 8.3. it says that the 308XE providers internal biasing for receiver input threshold for open-circuit, bus-idle, and short-circuit. Thus I think it is an internal limit.

As for what will happen when a short circuit occurs the device will go into thermal shutdown failure and the outputs will be high impedance. This is also described in Section 8.3.

0 MIKHAIL SALOV over 9 years ago in reply to Matt Mendez

TI__Expert 7640 points

Thank you, Matt,

Mike

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SN65HVD3082E: SN65HVD3082E total power consumption for 256 loads