UC1825A: Compatibility issue with UC2825DW and UC2825AMDWEP

Hi Bhanu,

The devices are be pin 2 pin compatible.

Is the SS function on the IC been activated in the pulse skipping mode?

Regards

Peter

No. SS function is always high at 5V.

Hi Bhanu,

The older UC parts can be sensitive to negative voltages and currents on the gate drive outputs. Try connecting signal level schottky diodes between the OUTA and OUTB pins to see if the issue is resolved.

Regards

Peter

Hi Sir,

We connected Schottky diode between OUTA to Gnd and OUTB to Gnd. It didn't resolve the issue.

Regards,

Bhanuprakash CV

Which older UC parts and years, is there date region that has this issue?

Newer UC no longer have this issue, correct?

Hi Richard,

All UC parts are based on a bipolar process and some of the devices can be sensitive to negative voltage and currents on the gate drive pins. PCB layout and ground returns have a large part to play in this. In some cases we have found it beneficial to add diodes between the gates drive output pins and ground.

The newer devices are UCC and are based on a CMOS process and the gate drive outputs circuits have difference characteristics to improve their robustness to this issue.

Regards

Peter

Hi Peter,

Bhanu connected Schottky diode between OUTA to Gnd and OUTB to Gnd. It didn't resolve the issue. Could you please share your comments ?

What the PN for CMOS version from UC2825. 

What is the variant between them?, are they 125C rated part?  

Thanks.

Hi Richard,

Sorry my explanation was not very clear, The UC2825 is an older part based on a biploar process. Unitrode release dnewer parts with the UCC prefix that are based on a CMOS process, Like UCC28C42 for example. In this case the UCC version was preceded by the UC3842 part.

However there is no CMOS version of the UC2825 device hence there is no PCN as all UC2825 variants are based on a bipolar process.

I hope this helps.

Regards

Peter

Thank

Is there CMOS equivalent of UC2825 to review to ponder for push-pull with total duty cycle of close to 100%

R. 

Peter, Richard,

Looking forward to your guidance resolving the customer issue on UC2825AMDWEP at the earliest.

Hi Richard,

There is no pin to pin CMOS equivalent but the UCC28250 and UCC28251 are CMOS push-pull controller with SR drive signals. There is also the UCC2808A and LM25037 as alternative push-pull controllers.

Regards

Peter

Hi Prahlad,

I went through the UC2825A datasheet and I see that in application schematics the OUTA and OUTB also have schottky diodes to the Vcc rail, see figure 12 page 10.

You could also try operating the UC2825A in open loop mode. Pull the FB signal load and load the EA OUT pin with a resistor to fix the duty cycle. The short circuit current capability of the voltage error amplifier is about 1.5mA. The max output voltage of EAOUT is 5V, so a 1.5k resistor will develop 2.25V level, the duty cycle might be a bit low but you can decrease the resistor value to increase the duty cycle to get a reasonable operating point.

Also try shorting the ILIM pin to 0V to eliminate it as a suspect.

Hope some of this helps.

Regards

Peter

Hi Prahlad,

I hope you have made some progress on this issue. Since there has been no activity on this post for a week I am going to close this post.

If you have more questions please open a new post.

Regards

Peter