Tool/software:
HI Raymond
below IC 4 which use the old date code work is ok, but change to new date code , the op 07 output will down to -0.7V when LOC111 output 0~5v swap
and the op07 surface very hot. i think maybe is the D2 conduction??
but old date code is ok?
LOC111 output 0~5v voltage
thanks
Hi Alex,
the op 07 output will down to -0.7V when LOC111 output 0~5v swap
and the op07 surface very hot.
If OP07's pin6 is measured at 5Vdc, then D1 will turn on, which it exceeds the diode's forward voltage of 0.65 - 0.7Vdc. There is not current limiting resistor at the IC4's output, so IC4 may source the max. current and it will get hot --> this may result EIPD event, if D1 is forward biased for a long time.
If IC3 is in Off state, OP07's input pin3 should be measured at GND. The IC4's output at pin6 should be measured at GND, and both D1 and D2 will be turned off.
If IC4 is powered with ±15Vdc in dual supply rails, IC4's output could go negative, because the voltage at pin3 is seen negative input voltage. If the negative voltage at pin6 is lower enough than -0.7Vdc, then the pin6 will show up at -0.7Vdc. In this scenario, current will flow into IC4 - again, there is not current limiting resistor between pin6 and current steering diode protection circuit. Yes, IC4 will get warm or hot depending on the current level.
but old date code is ok?
The IC4 output current protection has marginal design with the pair of current steering diodes, and it is not clear why pre-PCN does not have issues. The IC4 will get warm to hot in either pre and post PCN product. Are we comparing apple to apple scenarios between the two. Please let me know.
Best,
Raymond
hi Raymond
your are great, after check with R&D again, correct circuit as below
they say the diode which want to protect the ADC of MCU, but i think the circuit have a problem
use the old date code ,IC 4 is work ok
use the new date code , IC 4 is hot ,when LOC111 on/off switch
you can refer to the attach file before i already send you by private mail, thanks
Hi Alex,
use the old date code ,IC 4 is work ok
use the new date code , IC 4 is hot ,when LOC111 on/off switch
Please place 100Ω to 1kΩ resistor between pin6 and current steering diodes, the issue may be likely resolved.
The design in pre-PCN in OP07 is marginal, where the D1 (or D8 diode shown in the above image)diode is forward biased if pin6 voltage is shown at 5V, but the heating dissipation in IC4 is not obvious.
With the post-PCN OP07 product, the similar heat dissipation is heating up the IC4. By adding 1kΩ, see the image above, it will limit the output current and keep the IC4 cool. In addition, the post-PCN OP07C/D has slightly higher BW at approx. 1.4MHz, by inserting the resistor, it will stabilize the op amp and improve the phase margin. I suspected that there may be some parasitic capacitance at the IC4's output that may cause some of the unwanted behavior. The pre-PCN has BW specified at approx. 0.6MHz.
Please let me know if the above solution resolves the customer's issues.
Best,
Raymond
hi Ramond
thanks your reply ,
i agree your think , to limit the current output by a resistor in the pin 6 output of the OP07
I monitor the op07 output , when output down to -0.7v, pin 3 of IC4 still is 0v
may i know when the op07 will going to -0.7v?
LOC111 output is the 0~5v voltage, when switch the circuit in worse case,(0 or 5v), i will see the IC freeze and hot
due the ADC max only can acceptable 3.3v, so they use the top diode to did the 5v /3.3v transfomer
if this condition to result in the op going to -.0.7v, so down diode conduction .
thanks
