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PGA460: Questions for PGA460-EVM

Jun Ishida
Expert 5640 points
Part Number: PGA460
Other Parts Discussed in Thread: MSP-EXP430F5529LP,

Hello team,

Customer is currently evaluating the EVM (MSP-EXP430F5529LP + BOOSTXL-PGA460). The customer's sensor at transmitter side has 42.4Vp-p(+21.1Vp, -21.1Vp) specification.

1-1. The transmitter sensor is applied 120Vp-p (+60Vp, -60Vp) voltage because of Vpwr=7.5V and transformer=1:1:8.42. If OUTB XD1 (Pin#:T1-1) is open, the voltage which the transmitter sensor is applied is in half of 120Vp-p (60Vp-p)? If yes, is there any problem with using OUTB=Open?

1-2. If OUTB is not used, what is the recommended termination for this pin? (NC, tie to GND or pull-down/up?)

1-3. In above case of 1-1, the test result was that the voltage was -30V <=> +30V swing, not 0V <=> +60V swing. Is this behavior correct? Could you let us know the mechanism for +/-30V swing in case of 1-1 (OUB=Open)?

2-1. The customer would like to use the transformer with 2.5V center-tap, but the center-tap is connected with Vpwr on the EVM. Can the customer cut the center-tap connection to Vpwr(min.6V) and newly connect with 2.5V? Is there any problem with changing the center-tap voltage from Vpwr on EVM to 2.5V?

3-1. Could you provide the recommended 1:1:3 transformer?

4-1. If a transformer is not used and full-bridge circuit at MA40H1S-R side is used, we think below component change is needed. Is that correct?

       R30: Not mounted => Add 1kohm resistor

       R35: 0ohm resistor => Not mounted 

       R34: Not mounted => Add 0ohm resistor

Regards,

Ishida

  • 0
    TI__Mastermind 27950 points
    Hi Jun,

    In order to reduce the peak-to-peak excitation voltage at the transducer, reduce the PGA460's preset driver current limit (CURR_LIM_Px) register value. Assuming you continue to use a center-tap voltage at 7.2V and a 1:8.42 ratio transformer, you can use the PGA460's preset driver current limit register to control and reduce the peak to peak voltage at the transformer secondary and transducer side. Refer to the "PGA460 Ultrasonic Module Hardware and Software Optimization" ( www.ti.com/.../slaa732.pdf ) app note's section 4.3 Current Limit to observe how the I_Lim setting also impacts echo peak strength. When initially configuring the transducer for optimal peak-to-peak excitation voltage, start at an I_Lim of 50mA (minimum) and steadily increase until you've reached the desired peak-to-peak voltage at the transducer. 500mA is the maximum I_Lim value, which effectively yields the complete transformer ratio of 1:8.42, while 50mA is more likely to emulate a 1:2~3 transformer ratio.

    To create an additional reduction in addition to the 50mA minimum setting of the driver current limit, you can add resistance in series to the OUTA and OUTB pins. If the driver current limit setting does not help, you can reduce the center-tap voltage. In your proposal, you can source VPWR with 7.2V, and separately source 2.5V to the center-tap.

    For a full-bridge, mono-static configuration, additional components will be required when using the EVM. Refer to the following collateral for reference:
    • PGA460 Full-Bridge Driver Solutions for Ultrasonic Transducers ( www.ti.com/.../slaa780 )
    • PGA460 Mono-static Transducer Full-Bridge Driver Small Form Factor Design File ( www.ti.com/.../slac756 )
  • 0 in reply to Akeem Whitehead
    TI__Mastermind 27950 points
    Hi Jun,
    One additional note:
    If you are using the OUTA/B pins in either transformer single-ended mode or half-bridge direct drive mode, then the unused OUTx pin can either remain floating or pulled-low to ground through a resistor (i.e. 10k~100kOhm). The configuration is based on your preference. The OUTx pins are open-drain pins for the internal low-side nMOSFETs.