Graduate II

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Voltage admitted on an open drain output

Forum|Forum|1 year ago
June 1, 2024
2 replies
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Hello,

I need to drive some power mosfets (STP55NF06) from open drain outputs.

The gate and mcu output will be connected to a pull up resistor to 12V

Are the TT and FT pin voltage limits applicable when used in open drain mode?

If yes, I will amplify the 3V of a push pull output.

Else, it will reduce the design size.

Thanks for your reply

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Best answer by AScha.3

Hi,

you cannot drive 12V with the open drain mode. (Only kill the cpu. :) )

Anyway - what you want to switch with a 50A mosfet at super low speed ?

In ds its driven with 4,7 ohm - so you need a gate driver, to drive it at some speed.

With open drain mode you might just switch on a battery pack or so...no pwm.

S

STOne-32

Technical Moderator

Dear @xisco ,

Please refer to this Application Note AN4899 :

https://www.st.com/resource/en/application_note/an4899-stm32-microcontroller-gpio-hardware-settings-and-lowpower-consumption-stmicroelectronics.pdf

It will try to have the answer to the question .

Ciao

STOne-32

X

xiscoAuthor

Graduate II

Hello,

I see in AN4899 some things:

The diode marked in red in figure 1 prevents higher voltages than VDD+0.6V on a TT pin. For this reason, my design is not possible in TT pins.

The NMOS marked in red in figure 2 has to withstand 12V (VDS) when is off without being destroyed, considering the very low current current of my pull up resistor.

Chapter 5.1.1 does not specify, but seems to refer only to inputs.

Figure 1.png

Figure 2.png

A

AScha.3

Super User

Hi,

about cheap driver:

i use MCP 14E10-E/P ,

https://www.reichelt.de/de/de/3-0-a-dual-mosfet-treiber-2-x-nicht-invertierend-dip-8-mcp-14e10-e-p-p109723.html?r=1

+

a pulldown at the input, to be sure, its OFF at power up, until cpu pins get control.

+

or ...:

IR 4427S

https://www.reichelt.de/mosfet-treiber-low-side-so-8-ir-4427s-p129760.html?&trstct=pol_4&nbc=1

A

AScha.3Answer

Super User

Hi,

you cannot drive 12V with the open drain mode. (Only kill the cpu. :) )

Anyway - what you want to switch with a 50A mosfet at super low speed ?

In ds its driven with 4,7 ohm - so you need a gate driver, to drive it at some speed.

With open drain mode you might just switch on a battery pack or so...no pwm.

X

xiscoAuthor

Graduate II

Thanks for your reply.

It's for make a battery tester using different currents for different kind of batteries, drawing the discharge curve, calculating capacity and disconnecting when the battery voltage reaches the minimum voltage programmed.