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PGA460: PGA460 Half Bridge Drive deadzone problem

Farzan Saleem71
Prodigy 85 points
Part Number: PGA460

Hi,

I have been working on PG460 half bridge driver solution.I am using Murata MA58MF14-7N.The solution is working fine for long range but the problem is i am getting deadzone of 35cm even in short range preset setting.

I have tried a lot no matter what i do but the dead zone is consistent.Same setting work fine for transformer driven solution i am getting dead zone of about 18cm.Please help me to figure out the problem where i am getting wrong.Thanks


  TVGAIN0 = 0x44;
  TVGAIN1 = 0x44;
  TVGAIN2 = 0x44;
  TVGAIN3 = 0x08;
  TVGAIN4 = 0x64;
  TVGAIN5 = 0x9A;
  TVGAIN6 = 0x98;

  float transd_freq=58.0;
  FREQUENCY=(uint8_t)((transd_freq-30)/0.2);
  INIT_GAIN=0x00;
  DEADTIME = 0x80;
  PULSE_P1 = 0x10;
  PULSE_P2 = 0x15;
  CURR_LIM_P1 = 0x15;
  CURR_LIM_P2 = 0x71;
  REC_LENGTH = 0x19;
  FREQ_DIAG = 0x33;
  SAT_FDIAG_TH = 0xEE;
  FVOLT_DEC = 0x7C;
  DECPL_TEMP = 0x4F;
  DSP_SCALE = 0x00;
  TEMP_TRIM = 0x00;
  P1_GAIN_CTRL = 0x11;
  P2_GAIN_CTRL = 0x22;
 
 
  P1_THR_0  = 0x44;
  P1_THR_1  = 0x44;
  P1_THR_2  = 0x44;
  P1_THR_3  = 0x44;
  P1_THR_4  = 0x55;
  P1_THR_5  = 0x55;
  P1_THR_6  = 0x9C;
  P1_THR_7  = 0xD0;
  P1_THR_8  = 0x72;
  P1_THR_9  = 0x10;
  P1_THR_10 = 0x63;
  P1_THR_11 = 0x28;
  P1_THR_12 = 0x30;
  P1_THR_13 = 0x34;
  P1_THR_14 = 0X3C;
  P1_THR_15 = 0x00;

  • 0
    TI__Genius 11015 points
    FArzan,

    We have received your question & will respond to you in few days
  • 0
    TI__Mastermind 27950 points
    Hi Farzan,

    The issue of a longer dead zone in direct drive mode is expected in an ultrasonic sensor solution. The transformer offers counter inductance to help minimize the ring-decay time of the transducer. In half-bridge driver mode, you are limited to only using a damping resistor in parallel to the transducer to help minimize ring time, and are at the mercy of the transducer's resonant behavior.

    To improve the ring-time in half-bridge mode, you will need to ensure your initial time varying gain value is always 32.5dB to prevent the front end from saturating. You can ramp up you TVG level after a few hundred microseconds, but always keep your initial TVG level at 32.5dB. You can also try reducing the high-side driver voltage reference of the half-bridge. For instance, I was able to see downwards of 10~15cm in half-bridge mode using a Murata MA40S4S transducer at 5V with a damping resistor. If you need more information on the damping resistor, refer to section 3.4 "Passive Tuning" of the PGA460 Ultrasonic Module Hardware and Software Optimization app note ( www.ti.com/.../slaa732 ).

    Also, unless your application is automotive, you may want to consider using a different transducer. You can find a list of PGA460 compatible transducers at: www.ti.com/.../slac787