PNP BJT Transister - Inverter

[Docara]

Hello everyone,

I really struggle with transistors.

I am need to drive an active high Automotive High Side switch with an open drain (1-wire 28Vmax, 25mA max) Switch.

I realise I would need a PNP transistor and have come up with the following (ideal) circuit from a circuit simulation web site (link below) which gives a nominal 2mA current when conducting.
https://www.falstad.com/circuit/


I don't fully understand the datasheet terms and picking a suitable tranny, all the ones I find have a VBC of 5V - I need one a lot higher and the fact there are negative voltage around has pushed me over the edge.

I would be great full for some help in choosing a suitable SMD device and feedback on the circuit
Additionally, would a FET of some sort be better for low power applications - if so how what could be a suitable circuit and values.

Thanks
Edited to add a closed switch image to show values

[Ian.M]

I am need to drive an active high Automotive High Side switch with an open drain (1-wire 28Vmax, 25mA max) Switch.

Part numbers and datasheet links please.

[Docara]

Hi Ian

Here is the part number of the automotive switch ( there are others but they are all from the same family and depends on what I can get - supply issues obvs)
BTS5020_1EKA
https://www.infineon.com/cms/en/product/power/smart-low-side-high-side-switches/high-side-switches/profet-plus-12v-automotive-smart-high-side-switch/bts5020-1eka/

Its not to the datasheet directly but a quick rundown of parameters with a link to the datasheet below it
I've been trying to find a switch on current value but couldn't so have assumed it it purely voltage device

DS2413P
https://www.maximintegrated.com/en/products/interface/controllers-expanders/DS2413.html

Again its a quick reference page with an application circuit and there's a link to the actual datasheet

[Ian.M]

The BTS5020_1EKA has logic level control inputs that can be driven from 3.3V or 5V logic.  Applying 14V to its control inputs would destroy it.

A 2K2 pullup to logic Vcc on the DS2413P output(s) to get a logic level signal + a 4K7 series resistor between each DS2413P output and the BTS5020_1EKA control  input its driving should be sufficient.  Any inversion required can be handled in your application firmware.  The 4K7 resistor is for protection of the DS2413P during fault conditions - see 'Figure 52 Application Diagram with BTS5020-1EKA' in its datasheet.

[Terry Bites]

A Mosfet can be used but make sure its Vds is more than double your battery volts.

[Docara]

Hi Ian

Thank you for the reply, however I'm afraid I've dropped a big hairy one - and, embarrassingly, you've just found it for me!!!

Ages ago during original idea phase, I had accumulated quite a list of reasonable devices sorted for suitable for current and uC/DS2413 switching - anyway due to supply issues I checked to see which was available nowish and deleted the ones that will be available next century however I've deleted the wrong - list I've deleted the Vin = Vsupply list not the 3.3-5V logic one, and I can't find the deleted file

So, apart from my cock up posting here, I'm not going to be using logic level devices, so my original question still stands.

Thanks again

[Ian.M]

So what exactly *are* you going to be using?  If supply chain issues preclude specifying a particular part, please specify limiting values and an example part that meets them.

Note that a  DS2413P doesn't have sufficient output voltage rating for reliability in an automotive application if its used to directly level shift up to the +Vbatt supply! 

If however you can guarantee the supply transients *NEVER* exceed +28V or -0.7V,  you can drive a power P-MOSFET direct from the DS2413P, with a 10K pullup to the +14V rail, and either a 1K series gate resistor for MOSFETs with Vgs_max >+/-28V, or a resistor in series with the DS2413P output to form a potential divider to limit the gate drive swing for  MOSFETs with a lower Vgs_max rating. 

If you cant guarantee the +14V rail is free of objectionable extreme transients, you'll need to either cascode the DS2413P output with a transistor with adequate voltage rating, or use it to control  an inverting driver with adequate  voltage rating, and possibly diode clamp its output as well.    A 'jellybean' NPN with Vceo >120V and a 2K2 pullup from its base to the 5V logic supply should do the job,  either connected in cascode, with its emitter to the DS2413, or in grounded emitter, with its base pulled down by the DS2413 to turn it off.  Note that both configurations limit the voltage 'seen' by the DS2413 output to 5V or less, so are also suitable for direct drive from a 5V MCU pin.   Its possible to also use a MOSFET cascode, but selection of the MOSFET is far more critical, and it only saves one resistor and a couple of mA from the logic supply.