UCC27531: Boost Power to drive transducer

Hi Michael,

Thanks for reaching out and sharing your concern on UCC27531. Im an apps engineer and will help out.

The 531 gets its input from TDC1011 which has a peak current of ~1A therefore some limiting resistance on the input should be considered. The energy required to switch the transistor is the power dissipated in the driver during each cycle, for example with a capactive load the driver will dissipate C*V^2*Fsw where C=total gate capactiance and V=driver supply votlage. Any resistances in the drive loop that are not internal to the driver will absorb some power and draw heat away from the driver. The impedance model of the transducer will largely determine the peak current from 531 and therefore power dissipation since its a factor of V^2 for capacitive loads or I^2 for inductive loads.

A ballpark the power dissipation for a cap can be estimated by C * V^2 * Fsw assuming CV^2 = LI^2 we get L * I^2 * Fsw with L and Fsw fixed at for example 100uH and 100khz the only variable is how much current the driver will output. We can say the peak current is the difference in gate voltage, Vload divided by loop resistance, Rloop. I_peak = dVload/Rloop. If the inductor is mostly charged then dVload is smaller around 5v so I_peak is about 300mA if Rloop is 15 ohms. This makes about 1W of power dissipation using the equation above. The 1W will be divided amongest the resistors in the drive loop. Larger loads and frequencies will increase the dissipation.

You can check out an great app note on the Fundamentals of Gate Drivers section 2.7 on power losses:

Does this clear up some confusion? Please let me know if you have any more questions.

Thanks,

Hi Michael,

UCC27531 is capable of driving at 28V so long as the power dissipation of the part keeps the junction temp with in the datasheet rating 140 Tj rec op max.

At room temp the max power dissipation of UCC27531 is about 0.65W.

If we consider only the resistive portion of the transducer spec 254 ohms

V^2/R average power says that the transducer dissipates about 3W (and if the transducer voltage goes back to 0V then the transducer dissipates this power every cycle)

According to the ratio of resistances on the gate path 95% is from the transducer and will dissipate in the transducer.

This leaves only about 5% of total resistance in the gate path coming from the internal output structure of the driver.

5% of 3W is much less than the max power dissipation.

Can you sim or bench test this circuit to see the gate current waveform?

this will allow us to know how much current the driver is sinking and sourcing and therefore also dissipating.

We can take this current then multiply by Roh/Rol then we can know the real power dissipated internally every cycle.

Thanks,