I have used MC33078DR in many circuits; preamplifier circuits. All the parameters are in the imitation according to the datasheet. However, MC33078DR still has 2-5% failure rate after working 3-5 days. When MC33078DR gets damage, normally it burnt out near Vcc pin or GND pin.
I need some help, if there is anything I can do to solve this issue.
Thanks,
Ken
Hi Ken,
Could you share the schematic and operating conditions with us?
If you do not want to post the schematic in pubilc, you may choose friendship connect via E2E, where we are able to exchange private message through the forum.
I would like to know the additional operating information.
1. Vcc+ and Vcc- voltage rails and ripple and power supply source/sink current? Single or dual supply rails?
2. Did the damage occur at input or output or both?
3. The types of waveforms in Voltage, Amplitude and Current at input and output.
4. Operating ambient environment?
5. Any input or output transient conditions as you know of? What type of load are you driving?
Can you clarify the package orientation, where pin1 is located at upper right corner?
Best,
Raymond
Hello Raymond,
Thanks for your reply.
1. Vcc+ : 28V and Vcc- : 0V , ripple : 300mV , supply source/sink current : 0.6mA
2. when MC33078s are not working, the MC33078s can be no apparent damage, the damage near VCC+, and the damage near VCC+ and VCC-.
3. Audio waveform , Amplitude : 3Vpp , current : <1mA
4. 0~55℃
5. This is the instrumentation amplifier circuit. The output is connected to the input of class D chip.
There are three MC33078s in the circuit, and all of them have been burnt out.
Sincerely,
Ken
Hi Ken,
Please send me friendship request via E2E's private message. Once we establish a private contact, we can communicate and resolve the issues privately. In addition, I also have some questions about the part.
First, we will need to resolve 28Vdc ripple voltage issues with 300mVp-p. It seems that the application uses switching power supply that generates 28Vdc. What is the switching frequency of the switching power supply? What is the frequency ripple of 300mVpp? What is the operating BW of the op amp? What is input common-mode voltage for MC33078?
Although MC33078 can reject some of power supply ripple via PSRR (approx. 100dB near DC), the ripple rejection is only good at low frequency. The ripple frequency and amplitude will go through the op amp's supply voltage depending on ripple frequency, see PSRR plot on p.7 of the datasheet.
BTW, we also have alternative newer part that may be used to replace MC33078 for the future design information. The pricing of the OPA1678 is similar to MC33078.
Best,
Raymond
