• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 958 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM9061: PWM Application

Rick Hille
Intellectual 410 points
Part Number: LM9061
Other Parts Discussed in Thread: LM5060, LM555, DRV104, DRV103

I have a 24V resistive heater drive application that may either use hysteretic (thermostat) control or a PID loop utilizing PWM drive.   Since the mass being heated has a thermal time constant measured in seconds, the PWM frequency can be low, perhaps in the 10's of HZ.  The LM9061 appears to be a low cost solution for driving a high-side N-CH MOSFET with controlled slew to minimize electrical switching noise.  The datasheet Application bullet on the first page mentions PWM DC motor driver, but no PWM application info is presented.  

Since this is a simple, non-capacitive and low-inductive resistive element load of up to 2.5Amps, there will be minimal cold-inrush so I assume the delay timer can be minimal.  My understanding is that the delay timer has no effect on the ON-OFF times of the MOSFET, so I can just use the recommended non-specification Cdelay value of 0.1uF

Are there any PWM application examples I can examine and/or any particular points about this chip that I need to pay attention to?  The MOSFET I choose will be appropriately sized for the load current and as long as I don't alter the gate drive, I expect the repetitive transient power dissipation through the switching slews should stay well within the SOA rating.

  • 0
    TI__Genius 12380 points
    Hey Rick,

    To be honest, our team supporting LM9061 is not very familiar with designing for this particular application / end equipment.

    The LM5060 is very similar to the LM9061 but is lower cost and has some additional protection features (like UV/OV) and wider VIN range. Turn on time with LM5060 is longer due to smaller GATE sourcing current, but turn off time is quicker (due to stronger pull down current).

    It seems very reasonable and possible for these devices to be used as you are suggesting given the low frequency, but I would think a better or more common solution may exist. For example, do folks ever use a simple LM555 timer driving a low-side NFET these days?
    www.instructables.com/.../

    Otherwise I would think the motor drive specialists in TI may have better suggestions since in many ways, this application may be like a motor drive PWM control, but without the need for an H-Bridge.

    You can visit ti.com/motor for more information. Under the solenoid section, there are devices like DRV103 (low side up to 3A) and DRV104 (high side up to 1.5A) which look like they are designed for this area of end equipment but are quite old. If you think those devices may be more suitable, please post a new E2E thread with that GPN so the contacts related to that end equipment can assist you.

    Thanks!
    Alex
  • 0 in reply to Alex Triano
    Intellectual 410 points
    I guess the mention of PWM on the datasheet banner page caught my eye in the first place; I was hoping you had at least a few customers using the device in a LF PWM application, such as a DC lamp dimmer or, as suggested in the bullet, a DC motor speed control.

    The 5060 UV/OV features are not needed as this is an embedded application with well controlled power. the 5060 would have been suitable except that the gate slew rate will be slower and therefore will burn more power during ON transitions (I don't want to be force to a larger MOSFET with a larger SOA). I also don't want to use a traditional (fast) gate driver as I'd prefer not to have 10-20nsec transitions of 24V at 3Amps.

    I did consider a "hack" solution using a low-side N-MOSFET but controlling the Drain current slew is much trickier than a source follower topology using a high-side gate driver. I am familiar with the DRV series but didn't see a need for that type of device since the PWM will be supplied externally from a microcontroller IO (so no 555 either despite it being among my favorite hack ICs).
  • 0 in reply to Rick Hille
    TI__Genius 12380 points
    Hey Rick,

    I understand and wish we could provide more insight. Again, it may work for your application given the low frequency.

    That bullet indeed captured your attention, but that was probably included when the part first came out back in 1995. It's over 20x years old and since that time, its declined in popularity while newer parts like LM5060 have taken hold in other basic ON/OFF high power distribution circuits rather than those focused on PWM.

    Thanks,
    Alex