Voltage admitted on an open drain output

[xisco]

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

[STOne-32]

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

[AScha.3 · Accepted solution]

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.

[xisco]

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.

 

 

[xisco]

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.

[AScha.3]

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

[AScha.3]

So for just on/off , low speed switching, maybe cheap solution:

CD40109B-Q1  , quad Voltage Level Shifter ( 3V -> 12 V possible, 10mA " drive " )

https://www.mouser.de/ProductDetail/Texas-Instruments/CD40109BQNSRQ1?qs=HM7Ob9npyBJheowJq%2FZbcA%3D%3D

https://e2e.ti.com/support/logic-group/logic/f/logic-forum/1006390/cd40109b-q1-3-3v-to-12v-level-shifting

[AScha.3]

For a battery tester , controlled by 3v3 cpu, using some logic-level-mosfet would be my choice :

if 12V max. is ok and smd  : DMN1004UFV-7 , 55A , 5mOhm at 3v drive at gate ;

https://www.mouser.de/ProductDetail/Diodes-Incorporated/DMN1004UFV-7?qs=AQlKX63v8RsSMDlajGoD6w%3D%3D

if not so much current needed :

621-DMN3020UTS-13 (mouser)
DMN3020UTS-13 , 30V , 15A , 15mohm , 0,4..1 Vgsth , 44ct

821-TSM4806CSRLG

20V, 28A , 25mohm , 33ct

or more diy friendly : 

https://www.mouser.de/ProductDetail/Diodes-Incorporated/DMT6009LCT?qs=rN85NNvew%2FSKNXyjWLi4%2Fw%3D%3D