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LM2841-Q1: Difference LM2840/41/42-Q1

Part Number: LM2841-Q1
Other Parts Discussed in Thread: LM2841, LM2840, LM2842, TPS57060-Q1, TPS57060, LP2951, LM3489

Both have the same Rds,on and current limit, but the LM2840(-Q1) has better efficiency at 100mA, and the curve is still rising. Why is it only recommended up to 100mA (LM2841: 300mA)?

The curves for LM2841 and LM2842 look identical up to 300mA, does the latter go further just because of its current limit?

  • Hi,

    Are you referring to figure 2 and 3 on the datasheet? Yes, one of the difference is the current limit and also on the figure 2 the output is at 3.3V whereas in figure 3 the output voltage is 8V. You tend to have a better efficiency running VIN close to VOUT case.

    Thanks
    -Arief
  • I did not notice the output voltage in Fig. 3 was different from the first two, that explains the better efficiency. But then, what IS the difference between LM2840/41? Same FET, same current limit, why is one recommenden for 3x the current?

    One more thing, will the soft start feature work over temperature, when V_SHDN can go to 2,3V? Fig. 6 shows full current above ca. 2V. A "Too-Simple-Switcher"?

    In other words, is the TPS57060-Q1 a better choice for automotive? Its 65Vin sure make load dump clamping easier, it has a real SS pin, and I like to set the frequency myself.

    And guess what, it also has a brother with the same internal FET (TPS57160)! Reminds me of the opamps and references sold as "A" versions when they came out better at the end of the shift. Or the ...-10 Prozessors that would not start at 20MHz. But I'm starting to drift off, and it's not the tempco...

  • Hi,

    Yeah the main difference between the LM2840/41 series is the current limit trimming option. One is trimmed at higher current than the other.
    Also, i believe the soft-start should work over temperature.

    As for TPS57060, yes it offers more functionality as well more flexibility in your design in terms of adjusting the soft-start and switching frequency. Just make sure you done the webench simulation to select the compensation components such that works out.

    Thanks and i hope that helps
    -Arief
  • OK thank you. Think this is resolved now. Anyway some words what this is for:

    We settled for the LM2840 at 120mA max. behind some hefty voltage clamps, giving a 5V rail, and an LP2951 for 3V in the display unit (sitting remote from the ECU via CAN).

    The ECU gets an LM3489 + P-FET for 12V OR 24V Volt batteries (100% duty), giving regulated 12V for a valve. Another LP2951 gives a 5V rail, an MCP1661 boosts it up to 24V for a Sensor, and a linear regulator makes 1,8V for the DSP core. Only good thing is the DSP has 5V I/Os, so no 3V rail is needed here.

    If the customer used a 12V sensor or a 24V valve, or could decide on ONE battery voltage, we could save two of the 3 switchers.