DS16F95QML-SP: DS16F95QML-SP

Hi Rajan,

I will get you an answer by tomorrow at 12pm CT. 

Regards,

Tyler

Hi Rajan,

1. What is the power consumption of the DS16F95QML when both the driver and receiver are disabled?

A: At VCC = 5.5V, with both receiver and driver capability disabled, the device will draw max of 25mA. 

2. What is the power consumption of the DS16F95QML when the driver is operating but the receiver is disabled? 

3. What is the power consumption of the DS16F95QML when the receiver is operating but the driver is disabled?

A: To answer questions 2 and 3, it is hard to tell. The current draw will be somewhere in between 25mA and 28 mA. Typically, you will see more current draw when the driver is operating with receiver disabled vs. when the receiver is operating with driver disabled. The only way to tell for sure is to bench test this device measuring ICC @ VCC = 5.5V when you flip-flop /RE and /DE conditions.

4. What is the power consumption of the DS16F95QML when both the receiver are driver are operating?

A: At VCC = 5.5V, with both receiver and driver capability enabled, the device will draw max of 28mA.

Regards,

Tyler

Hi Tyler,

With Vcc=5V, would you expect the current draw to be slightly lower?

Would you describe the device as a 2-wire RS-485?

Kind Regards,

Rajan

Rajan,

With VCC = 5V I would expect the device to draw less current than if VCC = 5.5V. With less supply voltage, the internal driving/receiving circuitry will be biased with less voltage, and therefore reduce overall current draw from the supply. Even lower current draw when VCC = 4.5V. 

The DS16F95QML-SP meets EIA-485/422 standards. It can be used with RS485 compliant devices. 

Regards,

Tyler

Hello,

Will the 10-pin CFP package come with its leads formed or as is?

What are the thermal resistances for the three packages?

Thank you, Rajan

What value of decoupling is required between VCC and GND, and are any termination / pull-up/down resistors required on the physical-layer side?

Thank you

Hi Rajan,

The 10-pin CFP package will be packaged to specs listed in the datasheet on page 18. 

Thermal resistances for the three package types:

This is to answer your first reply. I am working on answering your question below.

Regards,

Tyler

Tyler,

Thank you for the thermal info.

I will connect the DS16F95QML to a MCU which has a four-pin UART interface, RX, TX, CTS and RTS. Can/should the CTS and RTS pins be connected to the DS16F95QML's enable inputs?

Kind Regards,

Rajan

Hi Rajan,

To answer your question about decoupling capacitors connected between VCC and GND, this will depend on how noisy your incoming supply is to the transceiver. Usually 0.01uF, 0.1uF, 1uF, etc., can be used to filter out high frequency noise. Place these capacitors as close to the VCC pins as possible to clean up the supply line before powering the transceiver. 

This is a RS422/485 compliant device that agrees with the EIA standard. You can expect RS422/485 differential signals to appear on pins A and B which will require terminating resistors between pins A and B. It is ideal to choose terminating resistor equal to, or more preferably 10% greater than the characteristic impedance of the cable (Zo) to eliminate reflections which allows higher data rates and longer cable lengths. Here is an app note that describes different terminating techniques: 

https://www.ti.com/lit/an/snla034b/snla034b.pdf

On the logic receive side pin RO, it would be helpful to include a weak pull-up resistor to VCC to keep the receive bus at a known state for the MCU. In the case the /RE is HIGH, the receiver will be turned off, and without the pull-up resistor, the RxD pin on the MCU will be left floating. 

It is possible that the CTS and RTS pins could be connected to the enable inputs of the DS16F95QML's enable inputs. RS422/485 doesn't have flow control, and it is up to your design both in physical and software to control the flow of communication between several devices. This could be one way to control the flow of communication to and from the transceiver by signaling the enable pins.

Regards,

-Tyler

It might be simpler to connect RTS to both the RE and DE inputs to control half-duplex communication?

Regarding termination, the following article is interesting: How to Properly Configure and Wire RS-422 and RS-485 Networks - Sealevel

Rajan,

If you connect the RTS to both RE and DE inputs, you can control when the driver and receiver are both on, or both off. You won't be able to individually control the driving or receiving portion of the device. If this works for your application, then this seems like a plausible solution. Keep in mind if you are in half-duplex communication, then you are only transmitting, or only receiving at one point in time. You can't transmit and receive simultaneously since half-duplex configuration. By connecting RTS to both RE and DE inputs, one side of the device, either driver or receiver will be idle and will consume power even though it is not currently in use. 

Regards,

Tyler 

Since neither rs422/485 use flow control, it's best to use two separate I/O lines to control the RE and DE inputs to maximise flexibility

Rajan,

If it were me designing the circuit, I would like to have separate control over the RE and DE pins, as it will give more flexibility for data flow control and will save on power when driver/receiver is not in use.

Regards,

Tyler

Why is Icc 25 mA when both RX and TX are disabled? This is a similar current draw and power consumption when one or both channels are enabled. Thank you

Tyler,

I am going to connect a 100 ohm differential resistor across A and B? Is this okay? What value of weak pull-up would you recommend for the logic-side RO input?

Rajan

On my PCB, I will add a 200 ohm differential termination resistor between A and B as well as a pull-up on the logic-side RO input. At the moment I do not know what the other end of the physical link will look like.

It would have been convenient if the device contained these fail-safe resistors internally ...