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Part Number: UCC27211
I use the UCC27211 in my project. In particular, I make the electrical circuit as in the datasheet in the half bridge configuration. In this moment, the Vhi and Vli pins are connected to ground and the Vhs pin is not connected to the transformer. I use 9V for UCC27211 and variable boot voltage from 6V to 24V for half bridge mosfet.
My problem is on Vhs pin because I always measure a constant voltage (close to the supply voltage). But if Vhi and Vli are at logical level voltage, in Vhs the voltage it should be zero. It's right?
If I disconnect the high side mosfet, the voltage on Vhs is always present.
Please, can anyone help me?
Hi Donatello, I am an applications engineer on TI's high power drivers group and will work with you to solve your questions. Can you elaborate on the following, "But if Vhi and Vli are at logical level voltage, in Vhs the voltage it should be zero. It's right?" Do you mean if HI and LI are both high? regards, Mateo
In reply to Richard Herring:
Dear Mateo and Richard,
thank you for reply.
I did a step-down switching that works perfectly (150Khz), while in half bridge configuration and high frequency (1MHz) I have many problem. At present, unfortunately I burned 6 MOSFET driver. In my test circuit, the LI and HI pins are always low (ground), VDD is 8.7V. Only low side MOSFET is connected and the other pins (HB, HO, HS) are disconnected. There is a voltage of 6.6V on the HS and HO, while on HB there is 8.1V. if I connect a capacitor or a resistor between HS and ground, the driver supplies the load until it burns.
if I connect the side high MOSFET and the bootstrap capacitor, on HS there will be the bootstrap voltage. The voltage on HO will be slightly higher than HS. After the driver burns.
In the step-down synchronous configuration, when HI and LI are low, no voltage is present on HS and HO.
Unfortunately I can not solve the problem.
In reply to Donatello Amicone:
this is my schematic:
The UCC27211 is supplied with 8.5V. The Vpower is variable from 6V to 30V. The signal in HI and LI pins are TTL with frequency of about 1MHz and 50% DC.
If I disconnect the transformer and Vpower, there is a voltage of about 6.6V on the HS pin and 8.1V on HB pin. In this case, if I connect a small capacitor on HS, it charges.
If I connect the transformer and increase the Vpower from 0V to 30V, sometimes the driver breaks down just after I enable the input signal on LI and HI.
I'm currently using more MOSFET in my tests, that have the following characteristics: Vds>=60V , Rds<200mOhm and Low gate charge <= 10nC .
Gate Driver Applications Engineering Manager
Dallas, TX USA
In reply to Don Dapkus:
these days, I've been designing a PCB following the advice of the forum. Now, I will have to solder the components and then I can do some good tests.
Therefore, I need more days before I can share results.
Hi,I made a PCB board with UCC27211. The frequency is about 994 kHz and Duty Cycle is 50%. The dead time is about 100ns.Below, the oscilloscope screenshot:
The yellow waveform is the gate signal high side and the blue waveform is the gate signal low side.
As you can see, there are peaks on the yellow waveform:
How can I improve the waveform for the high side?Thank you
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