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'[EE] Hot Chip needs cooling'
2005\10\14@150956 by Kevin

flavicon
face
Hi,
I created a small motor control board using a PIC and
a SN754410 DNE Motor Driver Chip.
I am powering two small motors, and they use about 700ma
amps each, when stalled. Each driver of the chip is
able to source 1100 ma, so I am in spec. However the
chip is getting pretty hot, how do I cool it ? It is a 16
pin DIP. I don't have any heat sinks for DIPs. I do have
some that screw on to a TO-220 package. Any way to attach
them or any other suggestions welcome.

Thanks,
Kevin


2005\10\14@152645 by marcel

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face
You could go to your local computer store and get a cooling kit for RAM. there
are two kinds: metal sleeves that slide over the entire strip, and those that
are just tiny bits of metal that are glued onto each individual RAM chip. You
want the latter kind. It won't be an exact fit, but it should work. I do
believe they usually come with thermal glue.
- Marcel

Kevin <spam_OUTkbenTakeThisOuTspamuniversal.dca.net> wrote:

{Quote hidden}

2005\10\14@154159 by Spehro Pefhany

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At 03:09 PM 10/14/2005 -0400, you wrote:
>Hi,
>I created a small motor control board using a PIC and
>a SN754410 DNE Motor Driver Chip.
>I am powering two small motors, and they use about 700ma
>amps each, when stalled. Each driver of the chip is
>able to source 1100 ma, so I am in spec. However the
>chip is getting pretty hot, how do I cool it ? It is a 16
>pin DIP. I don't have any heat sinks for DIPs. I do have
>some that screw on to a TO-220 package. Any way to attach
>them or any other suggestions welcome.
>
>Thanks,
>Kevin

Aavid Thermalloy has DIP-16 heatsinks, both slide-on and adhesive.
They are not expensive.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2005\10\14@154315 by Hopkins

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face
Make your own with a piece of metal folded in a "U" shape the mount on
top of the chip, use heat transfer paste in between the metal and the
chip.
To secure to chip you may need to devise something or possibly bend
metal tabs down at the ends of the chip to hold it in place, or make the
metal "U" have some other mounting arrangement to the board.

Or a cooling fan.

_______________________________________

Roy
Tauranga
New Zealand
_______________________________________

> {Original Message removed}

2005\10\14@155501 by Randy Glenn

picon face
You might try something like these: http://www.hobbyengineering.com/H1538.html

On 10/14/05, Kevin <kbenspamKILLspamuniversal.dca.net> wrote:
> Hi,
> I created a small motor control board using a PIC and
> a SN754410 DNE Motor Driver Chip.
> I am powering two small motors, and they use about 700ma
> amps each, when stalled. Each driver of the chip is
> able to source 1100 ma, so I am in spec. However the
> chip is getting pretty hot, how do I cool it ? It is a 16
> pin DIP. I don't have any heat sinks for DIPs. I do have
> some that screw on to a TO-220 package. Any way to attach
> them or any other suggestions welcome.
>
> Thanks,
> Kevin
>
>
> -

2005\10\14@155839 by Randy Glenn

picon face
You might try something like these: http://www.hobbyengineering.com/H1538.html

On 10/14/05, Kevin <.....kbenKILLspamspam.....universal.dca.net> wrote:
> Hi,
> I created a small motor control board using a PIC and
> a SN754410 DNE Motor Driver Chip.
> I am powering two small motors, and they use about 700ma
> amps each, when stalled. Each driver of the chip is
> able to source 1100 ma, so I am in spec. However the
> chip is getting pretty hot, how do I cool it ? It is a 16
> pin DIP. I don't have any heat sinks for DIPs. I do have
> some that screw on to a TO-220 package. Any way to attach
> them or any other suggestions welcome.
>
> Thanks,
> Kevin
>
>
> -

2005\10\14@155855 by alan smith

picon face
Depends on how hot.....but you probably need a heat sink.  You can cut them down to size from something larger, and even oversize.  Different designs cool more efficiently, but might even need a fan to move air across the heat sink.  To attach, you can use thermal epoxy, sil pad or it might even come with thermal tape on it.  But whatever you use, make sure its a thermal bond.  Double sided tape wont work, as its not designed for thermal bonding and will essentially make the heat sink useless.

EraseMEmarcelspam_OUTspamTakeThisOuTcarrietech.com wrote:You could go to your local computer store and get a cooling kit for RAM. there
are two kinds: metal sleeves that slide over the entire strip, and those that
are just tiny bits of metal that are glued onto each individual RAM chip. You
want the latter kind. It won't be an exact fit, but it should work. I do
believe they usually come with thermal glue.
- Marcel

Kevin wrote:

{Quote hidden}

2005\10\14@163732 by olin piclist

face picon face
Kevin wrote:
> I created a small motor control board using a PIC and
> a SN754410 DNE Motor Driver Chip.
> I am powering two small motors, and they use about 700ma
> amps each, when stalled. Each driver of the chip is
> able to source 1100 ma, so I am in spec. However the
> chip is getting pretty hot, how do I cool it ? It is a 16
> pin DIP. I don't have any heat sinks for DIPs. I do have
> some that screw on to a TO-220 package. Any way to attach
> them or any other suggestions welcome.

I saw a bunch of other replies, but I think they are answering the wrong
question.  I don't know what a SN754410 DNE motor driver chip is (no I'm not
going to look it up, that's your job), but it sounds like the wrong tool or
maybe its not driven the best way.  Your real problem is an inefficient
setup.  It's probably better to make it more efficient and therefore cooler
in the first place than trying to deal with the dissipation of a bad design
after the fact.

Are the motors DC, brushless DC, something else?  What voltage?  Unless
you've got a very unusual setup, it shouldn't require much waste heat to
drive them.  Since motors are inductors and have considerable mechanical
inertia, they are great candidates for PWM control.  The pass elements are
always either full on or full off so they dissipate little heat.  Most of
the losses will come from the voltage drop when on and the transition time
while switching between states.  Motors work fine with PWM at a few 100 Hz
so switching transition times should be minimal.  FETs with a few 10s of
mOhms on resistance are readily available.  Or even bipolars might be fine
at such low currents.  200mV saturation x 700mA is only 140mW.

In any case we need more information about the motors, the available power
supply, and how the motors need to be controlled.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\10\14@230727 by Kevin

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face
{Quote hidden}

They are small DC Motors 1.5v to 3v.
0.18 - 0.25A at no load 0.70A +- 15% at max effic.
I am using 4AA NiMh batteries to power the board. I am
feeding th SN754410 with the raw voltage. The chip drops 3V
as per the data sheet. Right now I am not using PWM I just
have a logic high on the enable pin for each driver.
The datasheet is here for the SN754410
http://www.pololu.com/products/misc/0024/
but like I said as far as I know I am using the device
correctly.

2005\10\14@233752 by Mark Rages

face picon face
On 10/14/05, Kevin <kbenspamspam_OUTuniversal.dca.net> wrote:
{Quote hidden}

That's lousy!  3V drop * 0.7 A * 2 motors = 4.2 watts dissipated in
the chip.  Your batteries are spending as much energy warming the chip
as they are turning the motors!.  And, according to the datasheet,
"Continuous total power dissipation at (or below) 25°C free-air
temperature (see Note 2) . . . . . . . . 2075 mW"

So you are using the chip WAY out of spec.

As far as heatsinking this part, the center pins (closest to the die)
are ground and they form a heat sink when soldered to your ground
plane.  But you're going to have a real hard time dissipating 4W.

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2005\10\14@235010 by William Chops Westfield

face picon face
On Oct 14, 2005, at 1:37 PM, Olin Lathrop wrote:

> I saw a bunch of other replies, but I think they are answering the
> wrong
> question.  I don't know what a SN754410 DNE motor driver chip is, but
> it sounds like the wrong tool or maybe its not driven the best way.


The 754410 is TI's "improved" L293-style quad half-h-bridge chip, with
darlington output stages, and the associated significant voltage drops
and power dissipation.  I don't think it's possible to drive it
"improperly"
in the linear region, but the specs in the datasheet don't quite match
up; total power dissipation is 2W, but there are 4 drivers with ~1V
voltage drops, which is 4W at the rated 1A.  And even 2W seems like
quite a bit for a plastic dip16 package.

Do you already have significant copper area attached to the ground
pins that are designated for heatsink use as well?  If not, that
would be your first step.  The TI datasheet is unusually useless here;
there's better info in the ST sheet:
    http://www.st.com/stonline/books/pdf/docs/1328.pdf

Any chunk of metal is likely to be better than nothing; I'd be tempted
to take one of the TO220 heatsinks and some superglue as a first effort.
Copper sheet soldered to the designated pins would be better, of course.

The 754410 claims to have thermal shutdown.  If it's NOT shutting down
on you, then just saying "that chip runs hot" MIGHT be good enough,
depending on where your project falls on the "hobbyist hack to
critically
important commercial product" scale.

BillW

2005\10\15@000045 by Mark Rages

face picon face
On 10/14/05, William Chops Westfield <@spam@westfwKILLspamspammac.com> wrote:
> On Oct 14, 2005, at 1:37 PM, Olin Lathrop wrote:
>
> > I saw a bunch of other replies, but I think they are answering the
> > wrong
> > question.  I don't know what a SN754410 DNE motor driver chip is, but
> > it sounds like the wrong tool or maybe its not driven the best way.
>
>
> The 754410 is TI's "improved" L293-style quad half-h-bridge chip, with
> darlington output stages, and the associated significant voltage drops
> and power dissipation.  I don't think it's possible to drive it
> "improperly"
> in the linear region, but the specs in the datasheet don't quite match
> up; total power dissipation is 2W, but there are 4 drivers with ~1V
> voltage drops, which is 4W at the rated 1A.  And even 2W seems like
> quite a bit for a plastic dip16 package.
>

It's not a question of matching up, you just can't use all four
drivers at maximum current at 100% duty cycle.  I think datasheet
writers like to put the advantageous specs in bold on the front page,
and hide the gotchas in the fine print.   That's why you must read the
whole datasheet, of course.

Regards,
Mark
markrages@gmail

--
You think that it is a secret, but it never has been one.
 - fortune cookie

2005\10\15@083924 by Philip Pemberton

face picon face
In message <000001c5d0f7$82d342f0$0100a8c0@roy>
         "Hopkins" <KILLspamrdhopkinsKILLspamspamihug.co.nz> wrote:

> Make your own with a piece of metal folded in a "U" shape the mount on
> top of the chip, use heat transfer paste in between the metal and the
> chip.
> To secure to chip you may need to devise something or possibly bend
> metal tabs down at the ends of the chip to hold it in place, or make the
> metal "U" have some other mounting arrangement to the board.

Usually with high-power DIPs, the middle <n> pins are grounds and are often
thermally connected to the chip itself. I'd solder a copper (or maybe tin if
you're a cheapskate) heatsink onto them and rig a fan to move air over the
'sink.

All you need to do is bend the edges of the 'sink down, then cut some notches
so it doesn't short on the other pins.

Later.
--
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
RemoveMEphilpemTakeThisOuTspamphilpem.me.uk              | Athlon64 3200+ A8VDeluxe R2 512MB+100GB
http://www.philpem.me.uk/          | Panasonic CF-25 Mk.2 Toughbook
... SSC : Spare any Small Change?

2005\10\15@102448 by olin piclist

face picon face
Kevin wrote:
> They are small DC Motors 1.5v to 3v.
> 0.18 - 0.25A at no load 0.70A +- 15% at max effic.
> I am using 4AA NiMh batteries to power the board. I am
> feeding th SN754410 with the raw voltage. The chip drops 3V
> as per the data sheet.

Yikes!  No wonder it gets hot.  You've got about a 5V supply.  You certainly
don't want the driver elements dropping 60% of the voltage.  Your putting
more power into the drivers than into the motors.

> Right now I am not using PWM I just
> have a logic high on the enable pin for each driver.

So you only need to switch the motors on and off, not run them a partial
power?  If so, that's even easier.  Use a logic level N-channel FET as a low
side switch.  Since this is not constantly switching, the switching
transition time doesn't matter much.  Just drive the gate directly from a
PIC pin, source to ground, drain to the motor, and other side of motor to
+supply.  Don't forget the reverse diode accross the motor and put a small
ceramic cap as close as possible directly accross the motor to reduce
emissions and other nasties.

A small and cheap FET like IRLML2502 would be fine here.  It comes is a
SOT-23 package, but that doesn't matter since it won't be dissipating any
power.  700mA thru 45mOhms is only 22mW.  Many other FETs would be fine too.
The right NPN could be used too.  This is really not a very demanding job
for the pass element.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\10\15@181643 by Kevin

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{Quote hidden}

Yes, I guess I will have to switch the design to not use
that chip. :( I just didn't count on the heat
dissipation being such a problem.
I eventually wanted to be able to reverse the motors
and use PWM to keep them in sync. IE going in a straight
line. I just have not gotten that far with the code.

~Kevin

2005\10\15@191332 by Neil Baylis

picon face
Well, it sounds to me like you're on the right track. Why not just
start using the PWM.? The 754410 should work fine in that mode.
Exactly how hot is it getting now? Were you thinking of using a
current sense resistor to control the current through the motor, or
were you just going to run the PWM open loop?

Neil

2005\10\15@195655 by Kevin

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face
On Sat, 15 Oct 2005, Neil Baylis wrote:

> Well, it sounds to me like you're on the right track. Why not just
> start using the PWM.? The 754410 should work fine in that mode.
> Exactly how hot is it getting now? Were you thinking of using a
> current sense resistor to control the current through the motor, or
> were you just going to run the PWM open loop?
>
> Neil
>
Well, someone calculated 4.2 W and the chip is spec'd at
2.1 W, so pretty damn hot :).  I already had the boards
made :( so I will try a good heatsink and OPEN Loop PWM.
I will try running in a 50% duty cycle any suggetions on
freq ? Should I keep it high >20Khz, so the motors don't
chatter, or should I use a LOW freq like 200 Hz ?

Thanks,
Kevin

2005\10\15@201258 by Neil Baylis

picon face
Experiment till you find a frequency that the motors like, and your
ears like ;-). Also, even a small fan will help with the heat,
especially if you can, as someone mentioned, solder some copper to the
heat sink pins. If your board already has them connected to a healthy
ground plane, then just cool the board with a little fan to get the
heat away. Does it get too hot to touch? How long does it take to heat
up?

Neil

On 10/15/05, Kevin <spamBeGonekbenspamBeGonespamuniversal.dca.net> wrote:
{Quote hidden}

> -

2005\10\16@102238 by olin piclist

face picon face
Kevin wrote:
> Yes, I guess I will have to switch the design to not use
> that chip. :( I just didn't count on the heat
> dissipation being such a problem.
> I eventually wanted to be able to reverse the motors
> and use PWM to keep them in sync. IE going in a straight
> line. I just have not gotten that far with the code.

That chip is still not the right answer because its voltage drop is more
than half you supply.  You can make your own H bridge fairly easily.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\10\16@102630 by olin piclist

face picon face
Kevin wrote:
> I will try running in a 50% duty cycle any suggetions on
> freq ? Should I keep it high >20Khz, so the motors don't
> chatter, or should I use a LOW freq like 200 Hz ?

Lower is better electrically.  The mechanical inertia of the motor will
filter 200Hz fine.  The only reason for going higher is if the motor makes
objectionable noises.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\10\16@104212 by Neil Baylis

picon face
Olin,

> That chip is still not the right answer because its voltage drop is more
> than half you supply.  You can make your own H bridge fairly easily.

yes, of course it would have been better to start with a different
device, e.g. one that uses power FETs. But he already has boards made.
And his motors are tiny. He may be able to make it work satisfactorily
with what he has, although it won't be optimal.

Neil

--
http://www.pixpopuli.com

2005\10\16@150858 by Kevin

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face
On Sun, 16 Oct 2005, Neil Baylis wrote:

> Olin,
>
> > That chip is still not the right answer because its voltage drop is more
> > than half you supply.  You can make your own H bridge fairly easily.
>
> yes, of course it would have been better to start with a different
> device, e.g. one that uses power FETs. But he already has boards made.
> And his motors are tiny. He may be able to make it work satisfactorily
> with what he has, although it won't be optimal.
>
> Neil
Yes, live and learn. In my next board revision I will
probably use a Motorola 33887, which is designed around FETS.
However, with the suggestions I have received hopefully I
can work around the limitations of my current design. No pun
intended :)

Thanks to All,
Kevin

2005\10\16@182317 by Mark Rages

face picon face
On 10/16/05, Kevin <TakeThisOuTkbenEraseMEspamspam_OUTuniversal.dca.net> wrote:
> > Neil
> Yes, live and learn. In my next board revision I will
> probably use a Motorola 33887, which is designed around FETS.
> However, with the suggestions I have received hopefully I
> can work around the limitations of my current design. No pun
> intended :)
>

That's a fancy chip. but it needs at least 5 V.

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2005\10\16@200008 by William Chops Westfield

face picon face
On Oct 16, 2005, at 7:42 AM, Neil Baylis wrote:

> of course it would have been better to start with a different
> device, e.g. one that uses power FETs.

The L293 is a very popular H-bridge driver chip.  surely someone
offers a mosfet-style pin-compatible?

BillW

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