can a 5v sensor be interfaced witih lpcxpresso 1768 through adc?

anamr · Sep 12, 2011

hi
I thinking of using lpcxpresso 1768 dev board for my project. Lpcxpreso 1768 board is arm-cortexm3 based board with high embedded computing power. And its a low powered device (3.6volts). the datasheet mentions the adc has input range between VREFN to VREFP and max vdda of 3.6 volts .I am in a lil doubtful if i can interface the 5volts 3-axis analog accelerometer to it becuz it is powered at 3.6volts. Kindly clarify me if the controller has adc range 0-5 volt, so that i can directly connect analog o/p to adc pin or Do i have to convert analog sensor values from 5v to 3.6 v by some additional hardware and then feed the data to the adc pins?.Here the schematics of the board
Thank you....
View attachment plugin-LPCXpressoLPC1768revA.pdf

BradtheRad · Sep 17, 2011

It's not specifically stated on the datasheet as to what max voltage is safe to apply to a pin.

The usual warning for ICs is not to exceed 1/2 volt above or below the supply pins. To exceed this on any pin is to risk ruining the chip.

So it's wise to attenuate the 5V device output by using a simple resistor divider, or in some way to ensure it won't exceed 3.6 V going into the 3.6V powered device.

alexan_e · Sep 17, 2011

Page 575 of the user manual

ADC inputs: Warning: if the ADC is used, signal levels on analog input pins must not be above the
level of VDDA at any time otherwise, A/D converter readings will be invalid. If the A/D
converter is not used in an application then the pins associated with A/D inputs can be
used as 5 V tolerant digital IO pins.

The absolute max values are described in page 42 of the datasheet

You have to reduce the accelerometer output to a level up to VDDA

Alex

anamr · Sep 17, 2011

Thank you.
I did some expirements on sensor and the accelerometer is giving max analog o/p 2.4v so i guess pretty safe to connect with 3.6v adc pin of uc. The break out board is powered with 5 v. But i figured it out that ,there is a tiny regulator on breakout board giving 3.6 v to sensor.
I think my problem is solved ,thanks for all you help.

can a 5v sensor be interfaced witih lpcxpresso 1768 through adc?

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