UC3825: Device Recommendation

Xing He

Intellectual 2025 points

Part Number: UC3825
Other Parts Discussed in Thread: UCC27211, LM5036

Hi Team,

My customer wants to design a buck converter, they would like to choose a device like UC3825 which has the Vref pin. So that they can adjust the reference voltage.

And duty cycle up to 85%.

My questions:

1. Do you have other devices like UC3825 can be recommend?

2. The drive current of UC3825 is 1.5A (peak), can I use the UCC27211 follow with the UC3825 to improve the drive ability?

Thank you.

over 4 years ago

0 Teng Feng over 4 years ago

TI__Genius 13660 points

Hi Xing,

1./ I just want to check the requirements with you, do you want a device, which has two complementary outputs, and the maximum duty cycle of each output is larger than 85%?

2./ Yes, UC3825 can be used as the input of driver UCC27211. But please note that the maximum input rating of UCC27211 is 20-V.

Regards,

Teng

0 Xing He over 4 years ago in reply to Teng Feng

TI__Intellectual 2025 points

Hi Teng,

Actually, I want to a device have the Vref voltage can be adjusted. My customer wanted to use UC3825 to design a charger.

Yes, the maximum is larger than 85%.

Do you have similar device to recommend?

Thank you.

Best Regards

Xing

0 Teng Feng over 4 years ago in reply to Xing He

TI__Genius 13660 points

Hi Xing,

As I know, we don't have a device whose REF can be regalated.

I don’t think UC3825 can be used in this application. The toggle flip-flop in the block diagram means that the max duty cycle per output you will get with this device is 50% duty. The maximum duty cycle 85% in the datasheet applies to the comparator not the outputs. If you are driving a push-pull design, then the total duty cycle will be up to 85%, put each half will only see half of that. Since you want to operate a synchronous buck coveter and the two outputs are referenced to ground. Output A and B are totem pole and alternating, thus their duty cycle of two outputs will be the same.

TI has many synchronous PWM Buck Controllers you can consider.

http://www.ti.com/power-management/non-isolated-dc-dc-switching-regulators/step-down-buck/buck-controllers-external-switch/products.html#p2192=Multiple%20Outputs;Phase%20Interleaving;Synchronous%20Rectification&sort=p238max;desc

For this specs, I will also recommend half bridge topology and device LM5036.

Regards,

Teng

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UC3825: Device Recommendation