Forums

TCA0372 troubles

Started by George Herold June 4, 2019
I'm using my first TCA0372 as a ~1-2 Watt heater drive.  Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.  
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit.  Or another 
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.  

thoughts?
George H.   
On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote:
> I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately > I've blown it up three times... twice by accident and this morning on purpose. > Apparently the TCA can't have it's output shorted to ground. > I_out max is 1.0 A (DC), > https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF > > So I need either some output protection.. current limit. Or another > opamp that does ~100 mA, or I'll have to do some transistor pass element.. > it's dead slow so speed is not important. > > thoughts? > George H.
Say, Can I parallel opamps on the output for more current? How well will they share current? GH
On a sunny day (Tue, 4 Jun 2019 07:34:25 -0700 (PDT)) it happened George
Herold <gherold@teachspin.com> wrote in
<1a529d07-864a-46ed-9dfc-40eda1ee49af@googlegroups.com>:

>I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately >I've blown it up three times... twice by accident and this morning on purpose. >Apparently the TCA can't have it's output shorted to ground. >I_out max is 1.0 A (DC), >https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF > >So I need either some output protection.. current limit. Or another >opamp that does ~100 mA, or I'll have to do some transistor pass element.. >it's dead slow so speed is not important.
Transistor (current drive) or a MOSFET (voltage drive) is much better. Add some opamp for control. Or use the transistor or MOSFET itself as heater? http://panteltje.com/pub/heater_circuit.gif been working fine for many years. Drive is filtered PIC PWM output.. PID controller in software.
On Tuesday, June 4, 2019 at 10:56:08 AM UTC-4, Jan Panteltje wrote:
> On a sunny day (Tue, 4 Jun 2019 07:34:25 -0700 (PDT)) it happened George > Herold <gherold@teachspin.com> wrote in > <1a529d07-864a-46ed-9dfc-40eda1ee49af@googlegroups.com>: > > >I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately > >I've blown it up three times... twice by accident and this morning on purpose. > >Apparently the TCA can't have it's output shorted to ground. > >I_out max is 1.0 A (DC), > >https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF > > > >So I need either some output protection.. current limit. Or another > >opamp that does ~100 mA, or I'll have to do some transistor pass element.. > >it's dead slow so speed is not important. > > Transistor (current drive) or a MOSFET (voltage drive) is much better. > Add some opamp for control.
Right I might have to do that... it takes more thinking though. The opa551 looks nice. http://www.ti.com/lit/ds/symlink/opa552.pdf fig 29 shows how to parallel opamps.... I might try that with a different opamp. George H.
> > Or use the transistor or MOSFET itself as heater? > http://panteltje.com/pub/heater_circuit.gif > been working fine for many years. > Drive is filtered PIC PWM output.. PID controller in software.
On 6/4/19 10:49 AM, George Herold wrote:
> On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote: >> I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately >> I've blown it up three times... twice by accident and this morning on purpose. >> Apparently the TCA can't have it's output shorted to ground. >> I_out max is 1.0 A (DC), >> https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF >> >> So I need either some output protection.. current limit. Or another >> opamp that does ~100 mA, or I'll have to do some transistor pass element.. >> it's dead slow so speed is not important. >> >> thoughts? >> George H.
How about a ~10 ohm polyfuse? <https://www.digikey.com/product-detail/en/littelfuse-inc/600R150-RBZR/F5554TB-ND/1211304>
> > Say, Can I parallel opamps on the output for more current? How well > will they share current?
Fine, if you use separate feedback networks and a resistor in series with each one to limit the current consumed by duelling offset voltages. I often make 50-ohm outputs by parallelling two sections of an LT1260 CFA, each with a 100-ohm resistor in series. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately >I've blown it up three times... twice by accident and this morning on purpose. >Apparently the TCA can't have it's output shorted to ground. >I_out max is 1.0 A (DC), >https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF > >So I need either some output protection.. current limit. Or another >opamp that does ~100 mA, or I'll have to do some transistor pass element.. >it's dead slow so speed is not important. > >thoughts? >George H.
The data sheet is sketchy, if not evasive. It claims that the chip has thermal protections but warns against exceeding 1 amp out. There is nothing that specs actual current capability or current limit. Is your heater a resistor? That should limit the opamp output current. What's your supply voltage? One alternative to using a big opamp is to use a little one and boost its output using a 3t voltage regulator, LM317 or LM1117, as a power booster, essentially a smart, protected emitter follower. I've used the TCAs without problems, but I'm usually driving a fast output switch that has a final 50 ohm resistor, which takes a lot of stress off the opamp. Probably too much voltage drop x current can blow out a transistor before the thermal limit kicks in. Don't short the output! -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Tue, 4 Jun 2019 11:44:24 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 6/4/19 10:49 AM, George Herold wrote: >> On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote: >>> I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately >>> I've blown it up three times... twice by accident and this morning on purpose. >>> Apparently the TCA can't have it's output shorted to ground. >>> I_out max is 1.0 A (DC), >>> https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF >>> >>> So I need either some output protection.. current limit. Or another >>> opamp that does ~100 mA, or I'll have to do some transistor pass element.. >>> it's dead slow so speed is not important. >>> >>> thoughts? >>> George H. > >How about a ~10 ohm polyfuse? ><https://www.digikey.com/product-detail/en/littelfuse-inc/600R150-RBZR/F5554TB-ND/1211304> >> >> Say, Can I parallel opamps on the output for more current? How well >> will they share current? > >Fine, if you use separate feedback networks and a resistor in series >with each one to limit the current consumed by duelling offset voltages. > >I often make 50-ohm outputs by parallelling two sections of an LT1260 >CFA, each with a 100-ohm resistor in series. > >Cheers > >Phil Hobbs
I'm designing a laser controller that has to power five external energy sensors, 12v at up to 100 mA each. I've considered polyfuses in the 12v outputs, but if the customer shorts things, they can pull a lot of current before they heat up and open, which could reset my box. I might use some LDOs as non-regulators, just to get their current limiters. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Tuesday, June 4, 2019 at 11:44:34 AM UTC-4, Phil Hobbs wrote:
> On 6/4/19 10:49 AM, George Herold wrote: > > On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote: > >> I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately > >> I've blown it up three times... twice by accident and this morning on purpose. > >> Apparently the TCA can't have it's output shorted to ground. > >> I_out max is 1.0 A (DC), > >> https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF > >> > >> So I need either some output protection.. current limit. Or another > >> opamp that does ~100 mA, or I'll have to do some transistor pass element.. > >> it's dead slow so speed is not important. > >> > >> thoughts? > >> George H. > > How about a ~10 ohm polyfuse? > <https://www.digikey.com/product-detail/en/littelfuse-inc/600R150-RBZR/F5554TB-ND/1211304>
Huh, I've got some poly fuses... I always thought of them as slow.. but I could try. (I was thinking I could add some series R on the output, but inside the feedback loop...)
> > > > Say, Can I parallel opamps on the output for more current? How well > > will they share current? > > Fine, if you use separate feedback networks and a resistor in series > with each one to limit the current consumed by duelling offset voltages.
The OPA552 data sheet showed a master/ slave relationship with two opamps. George H.
> > I often make 50-ohm outputs by parallelling two sections of an LT1260 > CFA, each with a 100-ohm resistor in series. > > Cheers > > Phil Hobbs > > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > > hobbs at electrooptical dot net > http://electrooptical.net
On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote:
> On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately > >I've blown it up three times... twice by accident and this morning on purpose. > >Apparently the TCA can't have it's output shorted to ground. > >I_out max is 1.0 A (DC), > >https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF > > > >So I need either some output protection.. current limit. Or another > >opamp that does ~100 mA, or I'll have to do some transistor pass element.. > >it's dead slow so speed is not important. > > > >thoughts? > >George H. > > The data sheet is sketchy, if not evasive. It claims that the chip has > thermal protections but warns against exceeding 1 amp out. There is > nothing that specs actual current capability or current limit. > > Is your heater a resistor? That should limit the opamp output current.
Right, but kids have access to the output and can short it.
> > What's your supply voltage?
24V. (Here's a pic of the output.) https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0
> > One alternative to using a big opamp is to use a little one and boost > its output using a 3t voltage regulator, LM317 or LM1117, as a power > booster, essentially a smart, protected emitter follower. >
Huh.. 317 as power booster? I've used LM395 for that.. but they are spendy... How do I do that with an LM317? (and what's the dropout?)
> I've used the TCAs without problems, but I'm usually driving a fast > output switch that has a final 50 ohm resistor, which takes a lot of > stress off the opamp. > > Probably too much voltage drop x current can blow out a transistor > before the thermal limit kicks in. > > Don't short the output!
Then I can't sell it. :^) George H.
> > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
On 6/4/19 12:20 PM, George Herold wrote:
> On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote: >> On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold >> <gherold@teachspin.com> wrote: >> >>> I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately >>> I've blown it up three times... twice by accident and this morning on purpose. >>> Apparently the TCA can't have it's output shorted to ground. >>> I_out max is 1.0 A (DC), >>> https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF >>> >>> So I need either some output protection.. current limit. Or another >>> opamp that does ~100 mA, or I'll have to do some transistor pass element.. >>> it's dead slow so speed is not important. >>> >>> thoughts? >>> George H. >> >> The data sheet is sketchy, if not evasive. It claims that the chip has >> thermal protections but warns against exceeding 1 amp out. There is >> nothing that specs actual current capability or current limit. >> >> Is your heater a resistor? That should limit the opamp output current. > Right, but kids have access to the output and can short it. >> >> What's your supply voltage? > 24V. > (Here's a pic of the output.) > https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0 > > >> >> One alternative to using a big opamp is to use a little one and boost >> its output using a 3t voltage regulator, LM317 or LM1117, as a power >> booster, essentially a smart, protected emitter follower. >> > Huh.. 317 as power booster? I've used LM395 for that.. but they are > spendy... How do I do that with an LM317? (and what's the dropout?)
Just like the LM395. IIRC JT said that it's the same silicon with different metal. If you have more than one supply voltage involved, you might need some protection diodes. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net