SN65HVD1476: RS422/RS485 Receiver Power Dissipation

Hi David,

I don't think we have an app note on the receiver power consumption - but you should be able to calculate it with datasheet values.

Assuming the driver is disabled the power consumed is estimated by the following formula: P_RX = ICC * VCC + I_A*V_A + I_B * V_B + V_R * I_R. 

So I_B and I_A are the bus input current with a disabled driver and it gives the current at both ends of the common mode range - using a linear interpolation can prove to be a decent estimation tool for your design (its not perfect - but it will give you a ball-park estimation). So lets say for example V_I w.r.t. ground on the "A" pin is 12V and the voltage on the B pin is 11.5V we can estimate I_A = 240uA and I_B ~228.9uA. 

I_CC is equal to 650uA.

Now the I_R is going to be dependent on application but for illustration I will use the V_OH value at -8mA - but the power is just going to be |V_OH * I_OH| ; V_OH @ 8mA is going to equal to VCC - 0.3V (typ) 

For this example let VCC = 3.3V --> now we can put together our formula P_RX = 650uA * 3.3V + 12 * 240uA + 11.5V * 228.9uA + 3V * 8mA = 2.145mW + 2.88mW + 2.632mW + 24mW = 31.657mW (this will change depending on application)

So essentially you just need to look at all the pins during RX mode and ask : "What are all the pins voltages w.r.t. ground and what current is being sunk or sourced from those pins as they will indicate the power consumption of the device. For RX mode this is the R, A, B, /RE, and VCC pins (I didn't really include the /RE in the calculation as I assumed it was grounded, but it could add some power consumption. As a note some devices do not spec input current into A/B pins while in RX mode and instead spec input resistance - largely this just changes the format of the power at A and B pins but it is something to note. 

Please let me know if you have any other questions!

Best,

Parker Dodson