topic Re: About KM34Z256VLL7 AFE pins input range in Kinetis Microcontrollers

About KM34Z256VLL7 AFE pins input range

jeff-jianfeng_l — Tue, 23 Aug 2016 02:06:58 GMT

I'm using KM34Z256VLL7 in my design, the datasheet describe as follow, and I have some questions to check:

1. Is the full operating voltage range 2.7V~3.3V or -2.7V~3.3V.

2. I know the AFE inputs is 1Vpp differential and 0.5Vpp single ended ,if over the range the ADC result will be saturated, but I can't find the maxium and minimum input range about the AFE pins, if my input voltage is -2V~3.3V,will the AFE module be damaged.

Re: About KM34Z256VLL7 AFE pins input range

xiangjun_rong — Thu, 25 Aug 2016 06:57:44 GMT

Hi, Jeff,

I think the RM of KM family is confused, I will clarify it. Note that the SDADC only supports differential mode, the common voltage is from 0~0.8V, the P to P voltage is +/-0.5V in differential mode.

It is regarded as single ended mode if you connect the ADADMx to GND, but in the case, you have to use the differential mode regulation. The peak to peak voltage is +/-0.5V, the common voltage is from 0V to 0.8V. Because the P-P voltage is 0.5V, and SDADMx pin is clamped to GND, you can input 0V to 0.5V to SDADPx pin considering the common voltage is 0~0.8V. If the SDADPx pin is 0.25V, the SDADMx pin can be -0.25V.

the LSB is 1V/2**(24) so that you can calculate the volatge based on digital sample.

Hope it can help you

Xiangjun Rong

Re: About KM34Z256VLL7 AFE pins input range

jeff-jianfeng_l — Thu, 25 Aug 2016 07:52:21 GMT

Hi Rong

There are external signals input to SDADMx and SDADPx pins for sampling, the protection is necessary.

My question is what is the absolute negative voltage of these pins? Are the acceptable input voltage range -2.7V~3.3V? (of course i know the valid samping voltage is +/-250mV).

Another question is about the CM reference voltage 0~0.8V, if the SDADMx pin is clamped to 0.5V, what is the input range of SDADPx pin? --> 0.5V~1.3V? OR 0.5V~0.8V? OR 0.3~0.8V?

Re: About KM34Z256VLL7 AFE pins input range

xiangjun_rong — Thu, 25 Aug 2016 08:38:58 GMT

Hi, Jeff,

1)if the SDADMx pin is clamped to 0.5V, what is the input range of SDADPx pin?

>>>>The input range of SDADPx pin is from GND to 1V.

2)here are external signals input to SDADMx and SDADPx pins for sampling, the protection is necessary.

My question is what is the absolute negative voltage of these pins? Are the acceptable input voltage range -2.7V~3.3V?

>>>>>>Generally, there is internal diode which protect the ADC converter if the ananlog pin voltage exceeds the rating range, but the current should be less than 3mA.

If you input -2.7V for the ananlog pin with 1K serial resistor, I think it is okay, the chip can not be damaged.

Xiangjun Rong

Re: About KM34Z256VLL7 AFE pins input range

jeff-jianfeng_l — Thu, 25 Aug 2016 09:17:40 GMT

OK!

Thank you!