In this article, I will check the power consumption of different common RS485 to TTL modules. Please note that this is the total consumption of the module including LED indicators for some of the modules.
I will be using the same setup as part 1 with the temperature humidity sensor. Baud-rate:9600, 80 bit (include starting and ending bit) request and then a 90 bit reply data.
1. MAX485 module
Typical operating voltage: 5V
Sleep mode: No
Slew-rate limiting: No
Fail-safe circuitry: Output short-circuit protection, thermal shutdown
AutoDirection control: No
Data Rate: 2.5 (Mbps)
ESD-Protection: –
Module LED indicator: Power LED (always ON)
Maxim Integrated Datasheet: here
Average transmission current: 112.6mA
Average idling current: 4.7mA
Consumption time: 8.5ms (only consume power during requesting)
***The MAX485 module requires 5V power input as mentioned by the manual, please take your own risk when using 3.3v. But the communication looks normal with my own test, I test ran it for 60 mins***
Average transmission current: 35.86mA
Average idling current: 2.32mA
Consumption time: 8.5ms (only consume power during requesting)
2. SP3485E module
Typical operating voltage: 3.3V, 5V logic tolerant (module power input 3V-30V)
Sleep mode: R̅E̅ high and DE low for 600ns
Slew-rate limiting: No
Fail-safe circuitry: Driver output short-circuit protection
AutoDirection control: No (Yes, controlled by 74HC04 provided by the module)
Data Rate: 10 (Mbps)
ESD-Protection: 2kV
Module LED indicator: TXD indicator, RXD indicator
MaxLinear Datasheet: here
Let’s zoom in on the reply region and have a closer look. The current chart matches the RS485 signal.
Average transmission current: 1.67mA (requesting: 2.46mA, replying 1.11mA)
Average idling current: 321uA
3. MAX13487EESA
Typical operating voltage: 5V
Sleep mode: S̅H̅D̅N̅ pin
Slew-rate limiting: Yes
Fail-safe circuitry: TTL side hot swapping protection
AutoDirection control: Yes
Data Rate: 0.5 (Mbps)
ESD-Protection: 15kV
Module LED indicator: Power LED (always ON), TXD indicator, RXD indicator
Maxim Integrated Datasheet: here
***The MAX13487EESA module requires 5V power input as mentioned by the manual, please take your own risk when using 3.3v. But the communication looks normal with my own test, I test ran it for 60 mins***
Average transmission current: 6.26mA (requesting: 6.67mA, replying:5.93mA)
Average idling current: 5.5mA
4. SCM3721ASA signal isolation YD3082EESA module
Typical operating voltage: 3V-5.5V
Sleep mode: R̅E̅ high and DE low
Slew-rate limiting: Yes
Fail-safe circuitry: Receiver pulls high when receiver’s differential inputs are either shorted, open circuit, or connected to a terminal resistor
AutoDirection control: No (Yes, controlled by HC14 provided by the module)
Data Rate: 1 (Mbps)
ESD-Protection: 15kV
Module LED indicator: None
Datasheet: here
Average transmission current: 4.5mA (requesting: 5.27mA, replying:3.8mA)
Average idling current: 3.12mA
5. SCM3725ASA signal isolation SCM3406ASA module
Typical operating voltage: 3V-5.5V
Sleep mode: R̅E̅ high and DE low
Slew-rate limiting: No
Fail-safe circuitry: Receiver pulls high when receiver’s differential inputs are either shorted, open circuit, or connected to a terminal resistor
AutoDirection control: No (Yes, controlled by HC14 provided by the module)
Data Rate: 10 (Mbps)
ESD-Protection: 15kV
Module LED indicator: None
Datasheet: here
Average transmission current: 6.84mA (requesting: 7.66mA, replying:6.09mA)
Average idling current: 5.19mA
***2 transmissions failed out of 1358 trials ***
6. ADUM5401 DC-DC isolated SP485EE module
Typical operating voltage:5V (module power input 3.3V-5V)
Sleep mode: No
Slew-rate limiting: No
Fail-safe circuitry: Driver output short-circuit protection
AutoDirection control: No (Yes, controlled by HC14 provided by the module)
Data Rate: 10 (Mbps)
ESD-Protection: 15kV
Module LED indicator: Power indicator, TXD indicator, RXD indicator
Datasheet: here
Average transmission current: 109.71mA (requesting: 120.72mA, replying:102.06mA)
Average idling current: 72.27mA
Summary
Most of the modules work stable and reliable under my test environment and the code mentioned in the previous article, only the SCM3406ASA module has transmission failure, but only a small portion.
The Max485 is a no go in industrial applications, because it has no ESD protection but the same time high power consumption (But the MAX485 is the only few chips that offer industry qualifications such as MIL-STD-883B). Besides, the MAX485 chip is not any cheaper than the other chip such as MAX481. However, this MAX485 module is extremely cheap compared to the other modules. This could be a good starting point to test out your first RS485 circuit.
The ADUM54, SP485EE module is DC-DC power and signal isolated. If you are working in a harsh environment and do not have power contain, this module may be your choice.
The MAX13487EESA chip is the only chip that has auto direction control and hot-swaps protection. If you want to make your own module and do not want to add any hex inverter, this may be your choice.
The SP3485 module consumes relatively low power, if you are working with a power limited environment, this is your first go. And in part 3, we will dive deeper into SP3485 chip and make our own PCB.
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