UCC28951-Q1: UCC28951-Q1

Hello Rajasherkar,

The UCC28951-Q1 can achieve a maximum duty cycle of 95%. These devices are generally fallowed by a PFC pre-regulator and have been designed for 300 V to 410 V input. With a maximum duty cycle of 95% you should be able to obtain and input range of 3:1 if you desired.

You are correct that there are not input under or over voltage protection on these devices. I looked at the UCC28950-q1 and the UCC2895-Q1 devices and they don’t have this protection either.

You could build an input under shutdown circuit with a differential comparator. The output would control a FET tied to the soft start pin. In the case of an under voltage keep soft start pin shorted to ground.

I would recommend using this in peak current mode control, which gives you cycle by cycle peak current limit to prevent transformer saturation.

Regards,

Mike

Hello Rajashekar,

The following link will get you to application note that shows how to use a hysteretic comparator. http://www.ti.com/lit/ug/tidu020a/tidu020a.pdf

You can use the hysteretic comparator to drive a FET that can pull down on the soft start (SS) pin to disable the FET to turn of the gate driver when you desire.

To both input under voltage and output over voltage your best bet is to use primary side regulation. This is where the UCC28951-Q1 would be on the primary.

1. Input under voltage is the easy one. This would just require you to feed a resistor divider to the input of the comparator. This comparator would drive a FET and on an input under voltage condition would pull the SS pin of the UCC28951 low disabling the gate drive and reinitiating a soft start.

 

1. For output over voltage could put the comparator on the secondary that could be FED into a logic isolator that drives a logic level FET that is connected to the SS pin of the UC28951. In the case of an over voltage will pull the SS pin low.

Regards,

Mike

Hello Rajashekar,

In the figure no.55 & 56 of UCC28951-Q1 datasheet , Is there any over voltage and under voltage protection given in the input and output side of power circuit in the design of dc dc converter using UCC28951-Q1 ?
The UCC28951 does not have circuitry for input under voltage or output over voltage built in.
The UCC28951 does not have under current protection.

The design only has cycle by cycle peak current limit protection. The gate drive shuts down when
1. The CS signal is greater than 2V refer to figure 36 in the data sheet.
2. When setup in peak current mode control (Refer to block diagram on page 14)
a. The CS signal and PWM ramp is summed and sent to the PWM comparator (PWM Comp).
b. The gate drive will shut down when CS + RAMP > Comp.

Regards,

Mike