LTC6090: Using TFLAG to drive status LED

Hi,

You could try connecting a IC driver or transistor driver circuit discussed in this link at the connected OD and TFLAG pin.

Hope this helps.

Hi ARoxas,

I know how to drive an LED in principle.

But with the TFLAG output of the LTC6090 it's a bit special, as the only supply voltages available are +70V and -70V, the TFLAG pin has to stay within the limits of -3V and +7V to COM (ground), TFLAG can sink only a 70uA, and the LED shall light on when TFLAG goes low.

Any suggestions how to achieve this without a bunch of transistors, z-diodes and resistors?

Regards, Niels

Hello?

Anybody out there at Analog Devices who has some knowledge about the LTC6090?

9 Month ago, I had a question about how to light an LED in case of over-temperature condition.

I qould be very lucky to get an answer. Yes, any kind of answer would be helpful. Even the answer "sorry, we have no idea how to do this" would be ok if that's the way it is.

Niels

I see the quandry, and am asking for clarification on that abs max.

Hi Niels:

Apparently the pulldown NMOS on _tflag is limited to about 200uA (70uA and 330uA min/max limits are the last spec in the data sheet tables).  So it won't be able to drop too much voltage on the schottky/resistor load in its drain (see the simplified schematic).

That's not enough to drive an LED very well, so I would suggest a small pnp or p-channel FET.  Put the gate at _tflag, drain at com/ground, and let the source drive a series resistor and LED with its anode up at 5V or so.  If you don't have a supply handy, then you could try a superbright and see if 70uA (the min guaranteed) is enough to get you adequate illumination. 

Hi Glen,

thanks for answering. Unfortunately I got NO notification email.

So the frankly answer is that there is no way to simply light an LED with the LTC6090's TFLAG pin.
The intention for this pin is to use it with a microcontroller or some other kind of digital logic and its (lower level) power suplies.

This is ok. Would be nice if this is stated more clearly in the data sheet.

Thanks again, Niels

Hi Glen,

thanks for answering. Unfortunately I got NO notification email.

So the frankly answer is that there is no way to simply light an LED with the LTC6090's TFLAG pin.
The intention for this pin is to use it with a microcontroller or some other kind of digital logic and its (lower level) power suplies.

This is ok. Would be nice if this is stated more clearly in the data sheet.

Thanks again, Niels