topic Re: LPC845 _ADC Pin Reverse voltage limit in LPC Microcontrollers

LPC845 _ADC Pin Reverse voltage limit

PK_1114 — Fri, 20 Oct 2023 11:05:29 GMT

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

Re: LPC845 _ADC Pin Reverse voltage limit

ramprakash12 — Fri, 20 Oct 2023 13:31:32 GMT

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.

Re: LPC845 _ADC Pin Reverse voltage limit

xiangjun_rong — Mon, 23 Oct 2023 01:12:03 GMT

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

XiangJun Rong

Re: LPC845 _ADC Pin Reverse voltage limit

PK_1114 — Mon, 23 Oct 2023 04:01:33 GMT

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

Re: LPC845 _ADC Pin Reverse voltage limit

PK_1114 — Wed, 25 Oct 2023 11:21:09 GMT

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

Re: LPC845 _ADC Pin Reverse voltage limit

xiangjun_rong — Thu, 26 Oct 2023 05:16:02 GMT

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

XiangJun Rong