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dual or triple LDO output timing control

Kelly Wang
Intellectual 550 points

Other Parts Discussed in Thread: LP3996

My application needs to use 3.3V, 3.3V and 1.8V  power supply. So, I am looking for a LDO regulator that can output 3.3V, 3.3V, and 1.8V to minimize circuit size. Required power on sequence is: 1.8V-->3.3V_1-->3.3V_2. Somehow I can't find one. So, I try to use 

LP3996SD-1833/NOPB

 the dual one to reduce size a little. But its data sheet says there is timing control between out1 and out2. May I add an delay RC filter between Enable 1 and Enable 2 for controlling output timing between out 1 and out 2?

If you have another LDO with all 3 required output, it would be better.

Thanks,

  • 0
    TI__Guru 55940 points
    Hi Kelly,

    We do not have an LDO that will provide all three outputs in a single device. We do have multiple dual and single output LDOs that may be able to fit your requirements depending on your Vin, Iout, and PCB space requirements. Please provide these details if you would like help selecting LDOs, otherwise you can use our parametric search to input your application requirements:

    www.ti.com/.../products.html

    There are multiple ways to achieve the sequencing requirement as long as each output has an independent enable pin. Since you mention you are space constrained, you probably are not able to use either an external sequencer or voltage supervisor to provide the sequencing. You can use an RC delay on many of our LDO enable pins; however, some datasheets will state slew rate requirements for the enable pin. Perhaps the easier method would be to use LDOs that have an integrated Power Good (PG) function. For the space of a pullup resistor, you can still have a sharp edge on enable.

    LP3996 does not have any slew rate restrictions on Ven; therefore, your RC delay is a possibility with this device. LP3996 does have both the enable and PG function (POR); however, it is only on the output of the second regulator.

    Very Respectfully,
    Ryan