TLV803: voltage supervisor on dual rail with TLV803 and opto coupler

Davide Gironi

Part Number: TLV803
Other Parts Discussed in Thread: TLV809, , TPS3711, , TPS3760, TPS3847

Hello,

I would like to supervise output from a dual rail DC DC converter.

It's a 24V to +-15V output.

Basically what I'm doing it's build a voltage divider that output 5V from +-15V. Then use the -15V as the GND reference of a voltage supervisor and the 5V voltage divider output as VCC input.
The Reset signal has to drive the LED of an optocoupler, and it does it straight without any pull-up. The optocoupler so drive an N-Channel and a P-Channel for the +15 and -15 loads.

I'm at present using TLV809, but because it's push-pull I've problem driving the led outputs, cause the divider does not works well with 75k and 15k, so I've to use 75ohm and 15ohm. Also it warms up due to the current that goes through it.

I'm wondering if the new TLV803 could work like the first image below, or I have to add an NPN like below.. or other?

Thanks!

10 months ago

0 Jesse Villanueva 10 months ago

TI__Genius 14200 points

Hi Davide,

The TLV803E will not work for the second schematic due to the RESET pin will see both +15V and -15V, which will damage the device. You may use a voltage divider at the RESET pin to help with this issue. I would recommend using one of our wide Vin devices for this application. Either the TPS3711 or TPS3760 should work great for your application.

https://www.ti.com/product/TPS3711

https://www.ti.com/product/TPS3760

Jesse

0 Davide Gironi 10 months ago in reply to Jesse Villanueva

Prodigy 40 points

Thank you!
I've problem finding the TPS3711 or TPS3760.

Also I can not find any information about the max drain to source voltage of the open drain internal mosfet. In this circuit attached that is the one I prefer Vds will be 30V but I don't know if that's too much for the TLV803. Is that too much?

Thanks

0 Jesse Villanueva 10 months ago in reply to Davide Gironi

TI__Genius 14200 points

Hi Davide,

The RESET pin can tolerate up to 6.5V only.

The TPS3760 is a newer device that can tolerate up to 65V while the TPS3711 is an older device but it can tolerate up to 36V. If you need to order samples, the link I provided above will take you to the landing page of the products where you can order samples.

Jesse

0 Davide Gironi 10 months ago in reply to Jesse Villanueva

Prodigy 40 points

Thank you!
I'm able to find the TPS3847 108, 10V threshold, I'm thinking about it. Next week I will work on it.

0 Jesse Villanueva 10 months ago in reply to Davide Gironi

TI__Genius 14200 points

Hi Davide,

The TPS3847 is going to be better since the pins are tolerate up to 20V.

Jesse

0 Davide Gironi 9 months ago in reply to Jesse Villanueva

Prodigy 40 points

Do you think this one attached will work? Thanks!

note: 15Vint and -15Vint are the output from the DC to DC converter. GND is in common. -15V and 15V are the main output, that goes to the op amp circuit.

A) just use one TPS3847, push pull to the the 5V RESET (I think out is 5V) to the optocoupler.
B) 2 TPS3847. The +15V line check (actually 10.8V check) activate the -15V line output, while the -15V check activate the 15V line output.

+1 Jesse Villanueva 9 months ago in reply to Davide Gironi

TI__Genius 14200 points

Hi Davide,

I would go with your "B" set up for safety. I have tested the B schematic on my EVM and it worked fine.

Jesse

0 Davide Gironi 9 months ago in reply to Jesse Villanueva

Prodigy 40 points

Thank you,
I'll build a test board from our PCBA supplier to check it.
I've two more questions for you

1) If I've understood well: MR to VCC means that it auto/reset, every time VCC is above the threshold RESET is high again. MR to GND means if VCC goes below threshold RESET stay low until you pull MR high for a while to reset the circuit.

2) Can you check the A too in simulation environment. I don't have PSpice license to test it.

Thanks again.

0 Jesse Villanueva 9 months ago in reply to Davide Gironi

TI__Genius 14200 points

Hi Davide,

1) MR, Manual RESET pin, is an input pin which will drive the RESET output low if the MR pin is driven low. This pin needs to be kept high for the voltage monitoring of the VDD to be functional.

2) In your schematic A, there are instances when the RESET pin will see more than 20V, which is above spec for the device.

Jesse

0 Davide Gironi 9 months ago in reply to Jesse Villanueva

Prodigy 40 points

Thank you! All clear now.
I'll keep you updated as soon as I get the PCB manufactured. But I think it will all be ok.

0 Davide Gironi 9 months ago in reply to Jesse Villanueva

Prodigy 40 points

Find attached the tested circuit.
It works, no heat dissipated, below 10.8V almost or above -10.8V almost on the negative line the power line are truncated as requested.
Thanks again.

0 Jesse Villanueva 9 months ago in reply to Davide Gironi

TI__Genius 14200 points

Hi Davide,

Thank you for the great news. Happy to help.

Jesse

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TLV803: voltage supervisor on dual rail with TLV803 and opto coupler