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DRV8256PEVM: wrong part devices received.

N Chandra sekhar N Chandra sekhar
Intellectual 270 points
Part Number: DRV8256PEVM
Other Parts Discussed in Thread: DRV8436, , DRV8256, DRV8873, DRV8714-Q1

Hello,

we have ordered 3 nos of DRV8256PEVM ,on the board DRV8256PEVM is labelled, but when inspected, on 1 board DRV8X5X is labeled on the IC, in another 2 Boards DRV8436 is labeled on the IC. seems like same board EVM is designed to meet pinout of various ICS. but in our case we need to test DRV8256P. how can we test it.

our application demands 28V,5.5A DC brush motor. since on DRV8256P datasheet its mentioned it can handle up to 8A peak, can this chip  handle 5.5A to 6.5A continuous current.

1.is there any application note about PCB layout thermal recommendations?

2. can we connect 2 or 3 DRV8256P in parallel, like inputs & outputs connected together to increase current handling capacity. or to reduce overall heat generated.

thank you

with regards

Dr.N.Chandra sekhar,Phd

  • 0
    TI__Mastermind 37683 points

    Hi Chandra,

    N Chandra sekhar N Chandra sekhar said:
    seems like same board EVM is designed to meet pinout of various ICS. but in our case we need to test DRV8256P. how can we test it.

    Let me investigate this and I will get back to you within 24 hours.

    N Chandra sekhar N Chandra sekhar said:
    can this chip  handle 5.5A to 6.5A continuous current.

    The maximum continuous current will mainly depend on the PCB layout. This EVM can handle peak currents up to 8-A but a maximum continuous current of around 1-ARMS.

    N Chandra sekhar N Chandra sekhar said:
    is there any application note about PCB layout thermal recommendations?

    The following two resources provide guidelines for PCB layout design for motor driver applications. There are sections in the two resources on thermal.:

    1. https://www.ti.com/lit/an/slva959a/slva959a.pdf
    2. https://training.ti.com/ti-precision-labs-motor-drivers-pcb-layout
    N Chandra sekhar N Chandra sekhar said:
    can we connect 2 or 3 DRV8256P in parallel, like inputs & outputs connected together to increase current handling capacity. or to reduce overall heat generated.

    You can connect more than one driver in parallel to increase current capability. However, keeping the board and IC temperature low may be a challenge specially if you are planning on driving very large currents. You have to provide enough un-interrupted GND copper underneath the driver thermal pad to ensure the temperature is kept low. The two resources above also provide useful information on how to design a PCB layout with good thermal performance. 

  • 0
    Intellectual 270 points

    Hi Pablo,

    thanks for your reply.

    i am confused with your below reply

    Pablo Armet said:
    The maximum continuous current will mainly depend on the PCB layout. This EVM can handle peak currents up to 8-A but a maximum continuous current of around 1-ARMS.

    in datasheet of DRV8256 says continuous current  5A. but you are mentioning 1A RMS.. in our application the DC motor takes 5.5A. voltage is 28V. can this Chip  is a suitable part for our application or not.?

  • 0 in reply to N Chandra sekhar N Chandra sekhar
    TI__Mastermind 37683 points

    Hi Chandra,

    Can you please let me know where in the datasheet it specifies 5A continuous? We only specify peak current.

    The 1A-RMS is only relevant to the EVM. We have tested the EVM with continuous current and determined that 1-ARMS is the maximum current that it can handle before the IC temperature rise above 130C. If course, better cooling will allow the continuous current to be much higher before the device shutdown due to over heating.

    If you require 5-A continous, I think the DRV8873 may be a better option. This device has a max current capability of 10-A.

  • 0 in reply to Pablo Armet
    Intellectual 270 points

    Hi,

    our initial choice was to use DRV8873 . but presently its out of stock. and has a 35week+ lead times. i am seeing that most of the TI parts are out of stock and having more lead times.

    since its mentioned like 8A peak, we thought we can able to drive 5.5A continuous using the DRV8256P.  Now confusion is Can DRV8256P be used to drive 28V,5.5A DC motor or not. atleast lets assume we put 2 chips in parallel per motor..

    if not suggest us a way to achieve this driving if 28V,5.5A DC motor continous for hours together with the available stock of DC motor drivers.Thank you.

  • 0 in reply to N Chandra sekhar N Chandra sekhar
    TI__Mastermind 37683 points

    Hi Chandra,

    The peak max current for this device is 8-A. The device will go into overcurrent protection when the current is above 8-A for longer than 3µs. The IC temperature rise will limit the maximum continuous current. If the PCB can dissipate the heat very well, the IC may be able to operate at higher continuous current while preventing the IC temperature from increasing. In the case of the EVM, we measured that the maximum RMS continous current is 1-ARMS before the temperature is greater than 130C.

    One thing I forgot to mention about paralleling two driver is the input and output mismatch which can cause shoot-through. Since there can be some variation in the internal timers of both drivers, the outputs of each parallel output may not switch on at the same time and may cause damage to the driver. So I don't recommend going with this route.

    One solution that can work with the devices we have in stock is to use a gate driver with external FETs. The DRV8714-Q1 is a 4 channel half-bridge driver. Due to the much lower RDSon of external MOSFETs, you can get much higher continuous current.

    Let me know if you'll like me to provide more information about the DRV8714-Q1