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LMR16010 not synthesizeable with WEBENCH Designer

Other Parts Discussed in Thread: LMR16010, LM46001, LM2674, LM2585, LM46000

The candidat for new design LMR16010 is not synthesizable with WEBENCH Designer (Release Date: Fri Oct 7 12:30:57 2016, 1425413 bytes).

Result is always "Design cannot be created with this device.", no matter which parameters (e.g.: Vin Min = 30V, Vin Max = 35V, Vout = 26.7V, Iout = 0.6A, TA = 30°C)

Comment: "This design is not stable due phase margin either smaller than 35 or greater than 120."

  • Moving to Simple Switcher forum...
  • We will ask the Webench engineer to look in to this and address it as soon as possible. In the meanwhile, please let us know what your requirement is and we can help you out.
  • Our requirement are two output voltages.

    Input voltage: 20V .. 29V
    Output1 voltage: selectable 30V or 34V or 40V
    Output2 voltage: selectable 6V or 27V

    Our actual solution is a step-up switcher LM2585S-ADJ for Output1 (voltage selectable via switchable feedback resistors) and in serial a step-down switcher LM2674M_ADJ (voltage selectable via switchable feedback resistor).

    Because we need >500mA for Output2 (27V), and output of LM2674M_ADJ is instable when a 400mA load is connected totally, we want to replace by a new generation switcher, e.g. LMR16010. The system should also have a good EMC characteristic.

  • Is the input voltage range the same for the second output? The output voltage range for the second output (6V to 27V) is very wide. There can be stability issue with the use of LMR16010 too and you will need to adjust the value of L and COUT until you find a stable operating behavior. I would suggest choosing an L value that gives a ripple ratio in the range of 10% to 50% for the extreme ends of the output voltage range for the full rated load current. Also, choose COUT that gives a stable design for the lowest VOUT.

    For good EMC characteristics, I would suggest use of LM46001. This is also a 1A device, but it is synchronous and the package has a pin out that makes layout very easy for very good EMC.
  • The two switchers are connected in series, so the input voltage range of the second switcher is the output voltage of the first (30V .. 40V).


    The stability issue of LM2674 became worse, because we changed the Pulse PE-53818-S inductance (datasheet page 14, Ref. Design L18: 220uH) which has effective 252uH against a real 220uH (shielded) type. With an 330uH inductance it works more stable, but i am not sure about the disadvantage (except the max. DC current). Is there an disadvantage when the inductance is increased from 220uH to 330uH?


    LM46001 is a bit on the expensive side, but with internal diode it looks interesting for us.

    Can you also recommend an step-up switcher with good EMC characteristics to replace the LM2585 with 16mA Input Supply Current?

  • With increased inductance, the ripple current will reduce. For a device like LM2674 increased inductance will cause the L-C double pole to move to lower frequency and consequently make it difficult to be compensated for. Can you share some images of the unstable behavior that you are seeing? LM46001 actually has an integrated mosfet instead of a diode which should make the efficiency go up. The LMR16010 is a good replacement, but the LM46001 can help with EMI greatly compared to LMR16010.

    There isn't a new replacement for LM2585 from the SIMPLE SWITCHER portfolio, but you could find something easily on Webench.
  • First  picture shows stable situation (450mA load, ripple ~ 100mA), the other pictures the instable situation (0->450mA loaded).

  • Thanks for sharing these. It does look as if the device is not being compensated properly. Use of LMR16010 or LM46001 should make it easy to stabilize. The layout is going to be important. Therefore I suggest following the layout guidelines closely.
  • LM46001 looks very interesting for us. I have ordered the evaluation Module to test the switcher.

    There is also a 0,5A version LM46000 available. Is there a difference according the radiated emission whether we use LM46001 or LM46000 each with 0,5A output current? Which one has less radiation?

    Another issue is the switchable voltage (selectable via a parallel switchable Rfbb'): there are also varying feed-forward capacitors Cff, which can't switched. The challange is to find a design for 6.1V and 26.7V output voltage with similar Cff.

  • The radiated energy will depend on the switching frequency, input voltage and the load being driven. The 500mA design could potentially radiate a little less than the 1A design.
    It is true that the Cff will have to be chosen on the basis of a trade off between the farthest output voltages. But this should be manageable. If you use a top feedback resistor of 100kohms, trying to find a "middle-ground" value of Cff could become a bit easier.