Bandgap 1.2V reference voltage

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aleung
Level 2
Level 2
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On the CY8CKIT-062S4 Kit,   On the device configurator I set the AREF 1.2V to  output to the P10.2 pin and measure the voltage on P10.2 pin on the kit,   it reads a 1.28V  on the multimeter.    Isn't it should be 1.2V +/- 1% ?

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Vasanth
Moderator
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250 sign-ins 500 solutions authored First question asked

Hey,

One more way to measure the bandgap reference is to enable the internal reference bypassed mode in the ADC. This will enable pin VREF pin to connect an external bypass capacitor pin. You can measure the voltage on this pin, and see the value.

Best Regards,
Vasanth

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Vasanth
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250 sign-ins 500 solutions authored First question asked

Hi,

Ideally that is the voltage to be measured. But when you connecting to the pins additional parasitics will also come into picture I think ( for routing the signal). Can you rather try connecting the voltage to bandgap reference output and set the opamp in voltage follower mode and see the output ?

Best Regards,
Vasanth

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aleung
Level 2
Level 2
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- May I know how to set the "voltage follower" mode?

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Vasanth
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Hi,

You can configure the opamp in the following way.

Vasanth_0-1644929170753.png

Best Regards,
Vasanth

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aleung
Level 2
Level 2
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Hi, I got a notice of - the signal 'Ouput (internal only)' on 'OpAmp1' must not have connections when hidden........

wer.jpg

 

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Vasanth
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Moderator
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250 sign-ins 500 solutions authored First question asked

Hi,

My bad. You need the 10x driver as you are you are routing the signal to an external pin. Use the following configuration and try.

Vasanth_1-1644985154541.png

 

Best Regards,
Vasanth

 

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aleung
Level 2
Level 2
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Hi,

Complie and run, but the P9.3  measured as 0.0V.. I don't need to make h/w modification on the Kit right?

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Vasanth
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250 sign-ins 500 solutions authored First question asked

Hi,

The pins are multiplexed with capsense pads on the kit. 

Vasanth_0-1644991141216.png

You have to  populate R135 and remove R68 to see. But for quick testing you can check on the unpopulated R135 pad and check the voltage.

Best Regards,
Vasanth

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aleung
Level 2
Level 2
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Hi,

It give out the voltage 3.23v.

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Vasanth
Moderator
Moderator
Moderator
250 sign-ins 500 solutions authored First question asked

Hey,

One more way to measure the bandgap reference is to enable the internal reference bypassed mode in the ADC. This will enable pin VREF pin to connect an external bypass capacitor pin. You can measure the voltage on this pin, and see the value.

Best Regards,
Vasanth

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aleung
Level 2
Level 2
10 sign-ins 5 replies posted 5 questions asked

Hi,

The voltage on VREF pin is 1.27 volt.   I used this value to calculate the ADC reading on the input pin. This match the voltage value I feed to the input pin.   I'll use 1.27 as  VREF.

 

Thanks.

 

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