• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 46 subscribers
  • Views 332 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA2277: Question about OPA2277UA

Jimmy Huang
Genius 3525 points
Part Number: OPA2277
Other Parts Discussed in Thread: DAC8871

Hello:

In the process of using TI's operational amplifier chip opa2277ua and DAC chip dac8871, it is found that the operational amplifier chip opa2277ua has serious heating, with the temperature as high as 80 ~ 90 ℃. Please see if it is normal. At present, the following work has been done (the schematic diagram is attached at the end):

Note: the system is powered by 12V, and the required voltage is converted. Ni represents that the device is not welded.

1. Chip working voltage + 15V, - 15V, + 10V, - 10V, 3.3V oscilloscope test is normal;

2. After the system is powered on, the Vout of DAC is measured as 0V;

3. D28 and D29 have been removed;

4. Remove the resistor r127 in vrefh-f network, the total current of the system is reduced from 0.31a to 0.27A, and the temperature of opa2277ua is reduced to about 60 ℃. Remove the resistor r128 in vrefl-f network, the total current is reduced to 0.24a, and the temperature of opa2277ua is reduced to about 30 ℃.

  • 0
    TI__Guru* 93105 points

    Hi Jimmy,

    The OPA2277UA should not be getting hot under normal operating conditions. Something incorrect about the circuit or operating conditions could result in excessive heating. Here are some ideas that I think need to be considered:

    • U51 sides A and B appear to be operating as reference buffers but the feedback between their outputs and inverting inputs are not apparent in the schematic. VREFH-F and VREFL-F are shown driving very heavy capacitive loads 10 uF || 100 nF, that then connect to the DAC8871 inputs. The series resistance going to the capacitor from the Op amp outputs appears to be a zero Ohm shunt. If that is the case, the OPA2277UA may become unstable and oscillate because there is no isolation from the very high capacitive load. Oscillation often leads to excess current draw and heating of the Op amp. Use a 10x probe and wideband O-scope to check the U51 outputs for oscillation. Removing R128 would remove that high capacitive load from  the VREFL-F Op amp output and it would regain stability.

    • U46 is being operated as a unity-gain buffer. There is a high-value feedback resistor, R126, 6.2 k, in the feedback loop. That resistance in conjunction with the OPA2277UA input capacitance may be causing the buffer to become unstable. Use a 10x probe and wideband O-scope to check the U46 output for oscillation. If it is oscillating the Op amp can draw excessive current and become hot when dissipating the generated heat. It is best to not add a feedback resistor or keep its value to a minimum in many buffer applications.

    Let us know what you find.

    Regards, Thomas

    Precision Amplifiers Applications Engineering