TLC7226: Analog Voltage not set as per requirement

bhupendra suthar

Part Number: TLC7226
Other Parts Discussed in Thread: OPA192, LM358

Hello Team,

We are using TLC7226 for one of our DAC application.

Data line controls through STM32 I/O. But even when we changed GPIO to maximum , at certain point ( Decimal Values set by GPIO from D0-D7 ) voltage output decrease even increase in GPIO values.

Not Sure what happening wrong ?

Decimal GPIO data along with Output is attached here with excel.TLC7226IDW_analog.xlsx

over 3 years ago

0 Lucas Burnette over 3 years ago

TI__Expert 5100 points

Hi,

Can you please provide a schematic showing the connections of the system?

Thanks,
Lucas

0 bhupendra suthar over 3 years ago in reply to Lucas Burnette

Intellectual 515 points

0 Lucas Burnette over 3 years ago in reply to bhupendra suthar

TI__Expert 5100 points

Can you verify your digital signals using an oscilloscope or logic analyzer? Also please verify that your reference is staying at a constant 10 V.

0 bhupendra suthar over 3 years ago in reply to Lucas Burnette

Intellectual 515 points

Yes , we checked using DMM in voltage mode.

D0-D7 bits are set as per Data Value send by MCU pins.

Note :this is repeating issue , means we get error on output voltage each time we set on the SAME mentioned values ( Excel sheet).

0 Lucas Burnette over 3 years ago in reply to bhupendra suthar

TI__Expert 5100 points

Hi,

The simplest error would be if the digital inputs were miswired, so if you are able to use a logic analyzer, that could display all the digital lines together so I could see too.

Were you able to check VREF is staying at a constant 10V and is not noisy?

Is anything else connected to J15?

Thank you,
Lucas

0 bhupendra suthar over 3 years ago in reply to Lucas Burnette

Intellectual 515 points

J15 is just DAC output given to the LED to control its intensity.

VREF=10V is derived from 10K Potentiometer (R55) whose input is 12VDC from DC-DC converter as shown in Sch.

0 Lucas Burnette over 3 years ago in reply to bhupendra suthar

TI__Expert 5100 points

Hi,

Can you try adding a buffer between R55 and the VREF pin? You could also try connecting VREF directly to 12 V as well and see if you still are seeing the issue?

This could be an issue of the VREF current changing due to the R-2R DAC circuit, which may be affecting the R55 voltage drop.

(not from TLC7226, but a similar DAC)

Thanks,
Lucas

0 bhupendra suthar over 3 years ago in reply to Lucas Burnette

Intellectual 515 points

Can you suggest any buffer part to be placed in between ?

Thanks,

0 Lucas Burnette over 3 years ago in reply to bhupendra suthar

TI__Expert 5100 points

Hi,

The OPA192 is a high voltage operational amplifier that could fit your needs.

You could also use a direct 10V reference as well, like the REF5010.

Thanks,
Lucas

0 bhupendra suthar over 3 years ago in reply to Lucas Burnette

Intellectual 515 points

Thanks Lucas,

So , Should i use OPA192 as voltage follower configuration ?

Can we use LM358 in replacement of OPA as buffer ?

0 Lucas Burnette over 3 years ago in reply to bhupendra suthar

TI__Expert 5100 points

Hi,

Yes, you can use the OPA as just a unity gain buffer between the supply voltage and the DAC VREF pin.

LM358 should be fine since it is rated for up to 32 V.

Thanks,
Lucas

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TLC7226: Analog Voltage not set as per requirement