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Choosing an efficient regulator switch for dac7563.

Oscar Gomez Fuente
Expert 2066 points
Other Parts Discussed in Thread: OPA140, DAC7563, OPA2140, REF5025, TPS7A49, TPS7A30

Hi, I have the next DAC7563 design. I've got 3 dac7563, a total of 6 DACs with 6 opa140 to adapt the output signal from 0..5 volts to -5..+5 volts.

I need to feed  3 dacs dac7563 and the 3 opa2140 (6 opa140) and I'm not sure the most efficient way.

I dispose of a source of 12 Volts@1A(max) and I need the following voltages:

1º.- Va = +5 Volts to feed the 3 dac7563 and REF5025.

2º.-I though in use the ultralow-noise TPS7A49 (to get ultralow noise: +Vb = +5V) and TPS7A30(to get ultralow noise: -Vb = -5V) to feed the opa2140 ICs. But my big headache it is to choose an efficiently power switch to convert from 12Volts@1A(max) to 5Volt to feed the DAC7563 and REF5025 and another power switch to convert from 12Volts to +5V and -5V to feed the opa2140. Could anyone help me to choose this ICs?

Thank you so much. Best regards.

  • 0
    TI__Guru**** 191445 points

    There are many possible solutions.  The first thing you need to figure out is how much load current you require for each output voltage.

  • 0 in reply to JohnTucker
    Expert 2066 points
    Hi John,

    Thank you for you quick response.

    1º.- These DACs outputs are going to command the speed of 6 thrusters and according to the manufacturer the control signal has an impedance of about 2.5kΩ.

    Then when the output is V= 5 Volts:

    Imax = Vmax /R = 5V/ 2.5k = 2ma/thruster -> 12 mA the six thrusters.
    (From positive power supply)

    and when the output is V= -5 Volts:

    Imax = Vmax /R = -5V/ 2.5k = -2ma/thruster -> -12 mA the six thrusters. (From negative power supply)

    I'm not completely sure if the calculations must be done this way.

    2º.- According to the datasheet (Page 5), the power consumption of dac7563 in normal mode with internal reference off is maximum 0.5mA@5.5V -> 2.75 mWatts per dac7563, then 6 units * 0.5mA = 3 mA

    3º.- And the power consumption of the Vref from REF5025 is around:
    i) Vref from dac7563 (according to the datasheet page 5): 15uA. 6*15uA = 90uA
    ii) Vref from V- of the opa140: I@10k= (2.5 - .667*Vdac)/10k Imax (when Vdac = 0) = 2.5/10k = 0.25mA

    Total = 0.25*6 mA + 6*15uA = 1.59mA

    Total(1º + 2º + 3º) = 12mA + 3mA + 1.59mA = 16.59 mA

    Thank you so much.
  • 0 in reply to Oscar Gomez Fuente
    TI__Guru**** 191445 points
    Those output currents are generally a lot smaller than what I usually deal with (output currents in the 1 A to 12A range). I would suggest you input your requirements into the Webench design tool and see what it suggests.