msp430 input current

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Hi,

please refer to the device specific datasheet, usually you will find a section called "Absolute Maximum Ratings", and there is a specified value for "Voltage applied to any pin". This is basically the maximum voltage which the device can withstand.

However the maximum input voltage of the ADC is specified in the ADC section. For example, referring the MSP430G2553 datasheet which has ADC10 module, there is a section called "10-Bit ADC, Power Supply and Input Range Conditions (MSP430G2x53 Only)" and there you can find "Analog input value" sepcification specified between 0 - Vcc.

Just realized you are asking about "current" instead of "voltage", sorry, my mistake. I think in this case you can refer to here:

http://processors.wiki.ti.com/index.php/MSP430_FAQ#Maximum_GPIO_current_source.2Fsink

can i measure the current consumed per conversion by the adc of msp430

Hi,

it is usually also specified in the device datasheet.For example this is taken from MSP430G2553 datasheet:

this supply current is taken from vcc right? 0.6mA is current/conversion or what?

or what does that 0.6mA signify?

i also want how much current is withdrawn from input signal

GURU MOORTHY said:

0.6mA is current/conversion

And reference current. 0.25mA is reference current only, So when ADC is enabled and not converting, at 3V supply voltage it consumes 0.25mA. When converting - then consumes 0.6mA.

and what about the current taken in from the input signal at the adc input pin.

0.6mA is taken from vcc right?

GURU MOORTHY said:

and what about the current taken in from the input signal at the adc input pin.

As ADC input is capacitive, there's no constant input current to specify besides input leakage current which is very small, 50nA. ADC input current changes during sampling. More information: 2xx series User's Guide, ADC10 chapter "Sample Timing Considerations"

GURU MOORTHY said:

0.6mA is taken from vcc right?

Yes. It is clearly said in the datasheet table you were looking at. - Come on...

so, 0.6mA is the current per sample conversion. I think it is quite high.

GURU MOORTHY said:

so, 0.6mA is the current per sample conversion. I think it is quite high.

Take in account that at fastest ADC clock freq single conversion lasts just 2.06 microseconds. Calculate average current in case of 100 conversions per second and you will see that it is not even close to "quite high" as you say :)

The maximum input current is actually a maximum overvoltage clamping current. It is 2mA on each MSP pin. However, any continuous current >50nA indicates an overvoltage situation (input voltage > Vcc).

Besides this, the analog pins have an inrush current while charging the sampling capacitor. This depends on the capacitor size (different for different MSP families and ADCs, see the users guide) and the input switching resistance (typically 1kOhm). It can be up to 3.6mA (3.6V maximum input voltage on Vcc=3.6V) for the first picoseconds at the beginning of the sampling phase, then degrades quickly to 0.
In average, the input current (besides the up to 50nA leakage) is not a current but rather an input charge per conversion, that depends on capacitor size and input voltage.
If you multiply it with the number of conversion per second, you get charge per second and therefore average current.

 So much for the input currents. The other thing is the ADCs internal current consumption. It is found in the datasheet, as Leo has provided. this current depends on the conversion frequency (conversions per second), ADC frequency and some static base current. The datasheet lists a specific value for a specified ADC operating frequency, continuous operation and specified sampling time. Lower ADC frequency means lower current. Larger sampling time too.