LPC845 _ADC Pin Reverse voltage limit

[PK_1114]

Hi,

Is there any Reverse Protection in the LPC845 ADC pin, if there what is it voltage tolerance. I need to give the Sinusoidal wave to the ADC.

Thank You,
B Pavan Kumar

[PK_1114]

We are using the LPC845 ADC pins to measure the Charging and discharging currents of the Battery Bank in that negative Voltage is appearing at that Pin and it is working fine. 

hall effect Current measuring sensor +/-4V Output 

[xiangjun_rong]

Hi,

As ramprakash said that the ADC analog channel voltage ranges from GND to VDDA as the section 13.2 ADC in data sheet of LPC845

The limiting voltage for the analog channel pin ranges from -0.5V to 4.6V, if the analog voltage is outside of the range, the chip maybe damaged.

Hope it can help you

BR

XiangJun Rong

[ramprakash12 · Accepted solution]

The LPC845 does have protection diodes on its ADC pins, but the exact characteristics of these diodes are not provided in the datasheet. The protection diodes are designed to prevent damage to the chip from minor voltage overshoots, but they are not intended to be a primary protection mechanism against reverse voltage. If you expect that the ADC pin might be exposed to reverse voltage, it would be advisable to add an external protection circuit to prevent this.

As for the voltage tolerance, the LPC845's ADC pins are designed to handle voltages in the range of 0 to VDD, where VDD is the supply voltage to the chip. The exact maximum voltage will depend on your specific setup, but it will typically be around 3.3V. If the voltage on the ADC pin exceeds VDD (even briefly), it could potentially cause damage to the chip.

When applying a sinusoidal wave to the ADC, you need to ensure that the voltage of the wave never goes below 0V or above VDD. If the wave has a negative component, you will need to add a DC offset to bring it into the 0 to VDD range.

[PK_1114]

Hi @Ramprakash,

Can you please give an approximate characteristics of internal diode characteristics, as of now we are testing -3.3v on the Pin, at this time we didn't observe any failure.


Thank You,
B Pavan Kumar

[xiangjun_rong]

Hi,

As the following block diagram, I suppose that the ESD is implemented by diode, so if the pin voltage is out of the range from GND to 3.3V, the injection current will flow to VDD or GND from I/O pin, based on the spec of ESD diode, the maximum current is 2mA.

BTW, it is recommended to use external diode to protect analog I/O pin as the data sheet said:

Hope it can help you

BR

XiangJun Rong