MSP430FR6047: Calculating current limiter values for SCL,SDA,LCD-COM,TXD & RXD lines to increase battery life.

[pralay.p]

Hello Experts,

My application is a commercial battery powered device.

The 2 most important thing for me is to achieve "accuracy in metering" and "Increase battery life" of my product.

1st thing I'm able to achieve using MSP430FR6047 chip for water metering.

2nd thing is what I'm working on right now.

Logically current limiters are very helpful in achieving this, given I know how much of it to limit.

I'm unable to figure out where to start(optimization in software such as LPM mode's etc. already done).

Please guide me in this resistor calculation part as this is my first time doing so.

Any literature regarding the subject will also be highly appreciated.



Thanks in advance!!



Regards,

Pralay

 

[FvM]

I don't see how current limiting resistors should have an effect, except for well considered selection of I2C pull-ups. The respective interfaces have high impedance receivers and don't consume static current. Also LCD display is primarily a capacitive load, current consumption is determined by voltage and operation frequency.

Important parameters are correct initialization of each GPIO pin, avoiding floating inputs, well considered scheme for activation and deactivation of processor functions, power save circuits for external hardware.

 

[pralay.p]

Hello Experts,

My application is a commercial battery powered device.

The 2 most important thing for me is to achieve "accuracy in metering" and "Increase battery life" of my product.

1st thing I'm able to achieve using MSP430FR6047 chip for water metering.

2nd thing is what I'm working on right now.

Logically current limiters are very helpful in achieving this, given I know how much of it to limit.
I want to introduce current limiters on

1. RXD ad TXD of USART
2. COMM output Pins of LCD

I'm unable to figure out where to start(optimization in software such as LPM mode's etc. already done).

MCU used:

MSP430FR6047 - operating @ 2.5V

Interfaces used:


1. USART- Interfaced with RN2483 (operating @ 3.6V)via 74LVC2T45 i.e. Voltage level Translator
2. LCD operating @ 2.5V

Any literature regarding the subject will also be highly appreciated.


Thanks in advance!!


Regards,

Pralay

 

[KlausST]

Hi,

I´m not sure what you are asking for.

If you know the voltage and the current, then just use Ohm´s law.

****
I don´t know exactly where in the schematic and how you want to use those current limiters.
I agree with FvM... I don´t expect much benefit regading UART, I2C, display, IO....
None of the signal lines normally carry high current. All below 1mA.

****
I see a lot of vague informations. Nothing we can focus on.
****

Basically for battery operated systems:
* reduce idle current (no floating pins, disabling unused circuit / periferals. Using suitable switch mode supply circuits)
* reduce active time (fast wake up, using sleep modes wherever possible)

Klaus