[General] UART ttl signal level shifter with 2.7V supply voltage and low power MCU

Hello guys,
from past few days I'm dealing with LPC11U24 cortex M0 micro-controller.
I've a system with produce only 2.7V for entire circuit, in short my VCC is 2.7V(I've programmed MCU with power down mode using it's PMU).
In my code I'm using UART at 4800 baudrate.
Now cumming to the point, I need TTL level shifter(ic or any other circuit logic) which give at least vcc voltage for UART signal(i.e 2.7V).
If talk about max3232 or max202 then they all works with 3.3V or minimum 3.0V so they're not sufficient to work with 2.7V(I've practically tested before)!

After roaming on internet I've fount max218 which is capable to work between 1.8V to 4.25V but it is too costly for my low cost product!

so can any one suggest me proper solution for this stuff:???:

Use this circuit. The high side is connected to Tx of high side device.

Hi,

There are a lot of step up / boost DCDC converter chips that run with 2.7V or less.

Also there are capacitive voltage doubler / voltage inverter circuits. Like MAX1044..

If you have access to the other side of the RS232 (PC), then you maybe can use those (control line) levels to generate the RS232 supply voltage.
But this is a low cost solution, and you need to check if this is reliable enough for your application.

Klaus

pic.programmer said:

Use this circuit. The high side is connected to Tx of high side device.

Click to expand...

as i told you earlier my entire circuit has only 2.7V Vcc so how do i get 5V!!!!

- - - Updated - - -

KlausST said:

Hi,

There are a lot of step up / boost DCDC converter chips that run with 2.7V or less.

Also there are capacitive voltage doubler / voltage inverter circuits. Like MAX1044..

If you have access to the other side of the RS232 (PC), then you maybe can use those (control line) levels to generate the RS232 supply voltage.
But this is a low cost solution, and you need to check if this is reliable enough for your application.

Klaus

Click to expand...

voltage doubler and voltage compentation ic(i.e level shifter) are two different things!

at slave side I've device which has serial port with 3.3V level converter ic(may be max3232 or max 202)

Now if we come at CMOS logic level then VIH is 2.0V (for both, 3.3V and 5V),
in short at slave side i can easily get logic HIGH and LOW with 2.7V VCC supply
Am i Right????
https://learn.sparkfun.com/tutorials/logic-levels/33-v-cmos-logic-levels

Hi,

voltage compentation

Click to expand...

I don´t know what this is.

With a voltage doubler you can generate 5.4V from 2.7V.--> enough to operate a MAX232
With a voltage inverter you can generate -5.4V from 5.4V. --> maybe enough (for RS232 levels) to just use a CMOS switch instead of MAX232.

at slave side

Click to expand...

Is your device at the slave side or at the opposite side?
But isn´t RS232 the same for slave side and opposite (do you call it host?) side?

Now if we come at CMOS logic level then VIH is 2.0V (for both, 3.3V and 5V),

Click to expand...

CMOS levels are supply voltage dependent: about 0.3 x VCC and about 0.7 x VCC

Maybe you mean TTL or LVTTL levels?
--> But it depends on the IC. You should find the levels in the datasheets.

***

Please post a drawing or schematic of your whole communication circuit. I´m a bit confused at wich point you expect wich level.

KLaus

At slave side I've smart meter with serial port, now the system is, when i'll send appropriate commands from my master device(lpc11U24 circuitry)to the slave through serial (with 4800 baud rate )cable then it will reply with some bunch of data in string formats.

Now at slave side at serial port it has buffer ic(consider max3232), as my MCU voltage level is low then I'll not generate sufficient UART signal voltage by which slave can interpreter which one is HIGH or LOW

Regards,

HI,

I´m even more confused. I read all you previous posts and don´t know where you talk about supply voltage, where you talk about signal voltage and where you need the converters.
Please post a schematic or picture and clearly show where is the problem ... at wich voltage levels.

Klaus