Hot!Problem with TC7920

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marcelomendoza7
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2018/09/26 07:03:45 (permalink)
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Problem with TC7920

Hi everyone,
 
I'm using the TC7920 (Two Pair, N- and P-Channel Enhancement-Mode MOSFET with Drain-Diodes) to drive a ultrasound emitter (Murata MA40S4S, a piezo-electric transducer) with a ±10V signal, at 40 kHz. The MA40S4S transducer has a typical capacitance of 2550pF.
 
Without the transducer (load), the TC7920 output is very clean, but the problem appears when I connect the transducer to the output of the TC7920: the signal is distorted. On the datasheet, one of the applications is the drive of piezo-electric transducers, so, what is the problem with my application? The datasheet doesn't specify the range of the capacitance of the transducers that it can drive. The capacitance of my transducer could be the problem, I think, because it "charges" the TC7920, but the TC7920 should be able to drive my transducer.
 
Someone have had similar problems?
How I can solve my problem?
 
Marcelo.

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    alvieboy
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    Re: Problem with TC7920 2018/09/26 07:09:47 (permalink)
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    Can you show the gate driver and the currently observed output ? My first suspicion is you are not charging the gates quickly enough, or the target gate voltage is too low to switch the MOSFET fully on.

    Alvaro
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    marcelomendoza7
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    Re: Problem with TC7920 2018/09/26 08:42:11 (permalink)
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    Hi Alvaro,
    I'm using the Typical Application Circuit proposed by the manufactured: the driver is the MD1822. I power the VDD and VH pins with 10V, thus, at the outputs A, B, C and D, 10V signals are presented (wich are the amplified  inputs). 
    Sorry, but yesterday the IC TC7920 was damaged because I had changed one connection wrongly. I have the ±12V output of the TC7920 without the load (transducer), and the output of the MD1822.
    When I have new ICs, I will consider your sollution, because I never changed the +10V of the VDD and VH pins of the MD1822. I think the next week I will have the new ICs from Microchip.

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