CC1310: Design of DIO2_TXD and DIO3_RXD to UART1 of Quectel SC20

Ryan Reschan

Prodigy 40 points

Part Number: CC1310

Hello,

We are having issues with getting the CC1310 to interface with the Quectel SC20 module. The SC20 uses 1.8V logic level.

Quectel recommends using a voltage translator:

The initial design, however, used transistors to perform the translation:

We know Q1 circuitry works but Q2 does not. Even fixing that design so that it's flipped doesn't work.

Quectel also has this design in their knowledge base:

Using a voltage divider for the CC1310 RX to SC20 TX makes sense to me. In fact when I hook up a Launchpad to the SC20 UART with just a voltage divider, it seems to work just fine.

But going the other way with just a 1K resistor doesn't seem like it will work for the CC1310 when Vdds/Vdds2/Vdds2 is 3.3V.

Perhaps changing Vdds2 to 1.8V would be the way to go?

Here is more info on the SC20 UART:

From a TI perspective, is there a best design for this situation?

Thanks,

Ryan

over 4 years ago

0 RGW over 4 years ago

TI__Mastermind 33470 points

Hi,

Is it a valid option running CC1310 at 1.8 V as well ?

0 TER over 4 years ago in reply to RGW

TI__Guru**** 317180 points

See the datasheet, section 5.3 and 6.10 in https://www.ti.com/lit/gpn/cc1310. Min voltage is limited to 1.9 V if you are using a VDDS > 2.7 V.

I tried to find the datasheet for the module you are using but I believe I didn't find the correct one since it indicated a lot higher supply. Is it possible to run it on 1.9 V?

0 Ryan Reschan over 4 years ago in reply to TER

Prodigy 40 points

We are using the SC20AL.UART is up to 4 Mpbs. Voltage supply is 4.2V for the module from a LDO. Logic levels are all 1.8V. There's also regulated 1.8V power out of the module as well.

We use a LDO to get to 3.3V for the CC1310 from the 4.2V LDO.

+1 RGW over 4 years ago in reply to Ryan Reschan

TI__Mastermind 33470 points

Suggest to run CC1310 at 1.8V to solve this.

0 Ryan Reschan over 4 years ago in reply to RGW

Prodigy 40 points

Thanks Any particular reason why? Would the CC1310 have trouble driving the voltage translator?

+1 TER over 4 years ago in reply to Ryan Reschan

TI__Guru**** 317180 points

The answer is based on trying to find a configuration without an external level shifter. Since split rail required > 1.9 V one option is to run the CC1310 in external regulator mode (using VDD = 1.80 V)

0 Ryan Reschan over 4 years ago in reply to RGW

Prodigy 40 points

So I changed Vdds2 (pin 13) to receive 1.8V from the SC20 module's 1.8V LDO output and then bypassed the voltage translator circuitry. I was able to get it working.

There are two 1.8V LDOs on the SC20 module, one rated for 20mA and one rated for 100mA. Any idea if 20mA is okay?

0 Ryan Reschan over 4 years ago in reply to TER

Prodigy 40 points

So I changed Vdds2 (pin 13) to receive 1.8V from the SC20 module's 1.8V LDO output and then bypassed the voltage translator circuitry. I was able to get it working.

There are two 1.8V LDOs on the SC20 module, one rated for 20mA and one rated for 100mA. Any idea if 20mA is okay?

0 TER over 4 years ago in reply to Ryan Reschan

TI__Guru**** 317180 points

20 mA: Probably not. Look at the graphs under "5.20 Typical Characteristics" in the datasheet, the current consumption goes up using 1.8 V.

0 Ryan Reschan over 4 years ago in reply to TER

Prodigy 40 points

Vdds, Vdds3, and Vddr will still be 3.3V from a LDO.

Vdds2 is just DIO only, correct? I assumed we would only have to worry about driving the RX and TX lines to the SC20 module which are all sub-mA lines. Currently those will be the only DIO pins we'll be using on the module.

The graphs only show Vdds from what I can see.

I guess the other option is that we just use a voltage divider from the 3.3V LDO.

0 TER over 4 years ago in reply to Ryan Reschan

TI__Guru**** 317180 points

Running just VDDS2 = 1.8 V is not an option, see my previous reply:

TER said:
See the datasheet, section 5.3 and 6.10 in https://www.ti.com/lit/gpn/cc1310. Min voltage is limited to 1.9 V if you are using a VDDS > 2.7 V.

0 Ryan Reschan over 4 years ago in reply to TER

Prodigy 40 points

Ah, I see that now. So it looks like while my solution is working it's probably not a good long term solution and I need to figure out a different design.

0 Ryan Reschan over 4 years ago in reply to TER

Prodigy 40 points

For VDDR, can it be run at a higher voltage than VDDS?

For instance, can we run VDDS at 1.8V but then provide 3V to VDDS to use boost mode?

0 TER over 4 years ago in reply to Ryan Reschan

TI__Guru**** 317180 points

No. VDDR is an internal generated voltage which has to be 1.65 V when VDDS = 1.8 V (no boost)

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CC1310: Design of DIO2_TXD and DIO3_RXD to UART1 of Quectel SC20