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Connecting Decoupling Caps to Drain or GND?

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rhnrgn

rhnrgn

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Hello,

I am designing a circuit which's power is controlled via a mosfet by a MCU. Mosfet is placed between GND pin of component and GND line.

The point which is confusing me that, where to connect decoupling capacitors? To drain of N-type mosfet or directly to GND?

Thank You!
 

Can you show as the circuit? however I would say you should add it just from the gnd side.
 

At a minimum you should have a decoupling capacitor between the power and component ground of the component being switched (which is apparently the drain of the N-MOSFET).
 

Controlling power is best option instead of GND path....but if i am wrong, let me know why you are connecting/disconnecting GND's using MOSFET's
 

malli_1729 said:
Controlling power is best option instead of GND path....but if i am wrong, let me know why you are connecting/disconnecting GND's using MOSFET's
Click to expand...

Because i need to enable and disable it. It is laser diode driver circuit and MCU should have ability to enable and disable it. Diode needs 100ma thats why i can not source it from MCU.
 

Disabling a circuit, any circuit, by disconnecting its ground return path is not a good idea.

If you want to disable it, use a high side switch that disconnects your circuit from the power line.

Infineon, STMicro and others make plenty of high side switches, which allow you to control from 3.3 or 5v logic levels devices up to 40 volts at several amps. These HSS feature all sorts of protection mechanisms and status flags.
 

schmitt trigger said:
Disabling a circuit, any circuit, by disconnecting its ground return path is not a good idea.

If you want to disable it, use a high side switch that disconnects your circuit from the power line.

Infineon, STMicro and others make plenty of high side switches, which allow you to control from 3.3 or 5v logic levels devices up to 40 volts at several amps. These HSS feature all sorts of protection mechanisms and status flags.
Click to expand...

I have place for only sot23 bro =/
 

Disconnecting the ground line may give undesirable results, depending upon the rest of the circuit. If so then you would want to do a high-side switch (generally requiring one or two transistors). Can you post a diagram of the complete circuit?
 

crutschow said:
Disconnecting the ground line may give undesirable results, depending upon the rest of the circuit. If so then you would want to do a high-side switch (generally requiring one or two transistors). Can you post a diagram of the complete circuit?
Click to expand...

Of course i can but tomorrow. i am at home now. is this what we are looking for?

https://www.farnell.com/datasheets/1441824.pdf

Actually, we burned our half of laser diodes or laser diode drivers :/ can this be a reason?
 

rhnrgn said:
I have place for only sot23 bro =/
Click to expand...

Do an internet search.
The TPS27081A for instance, comes in a 2.9mm x 1.6mm TSOT-23 package.

There may be other solutions, this is just an example.
 


crutschow said:
That reference is for a high side switch. Are you using that to switch the ground side? If so, why?
Click to expand...

No i will use it at high side as you told me that high side switches better =).

Now i am designing a new PCB.
 

Can you give more details... What are the voltages available...Whether laser diode driver and MCU are powering from same supply. You require only Laser diode driver from MCU pins or an Isolated driver..... If you want to control only power means there are lots of IC's even smaller then SOT ...mostly load switches......simple laser diode drivers by googling gets these results "http://circuit-diagram.hqew.net/Laser$2ddiode$2dpulsers_17294.html
https://www.jameco.com/jameco/pressroom/puzzler1correct.html
http://www.repairfaq.org/sam/laserdps.htm" ...specify more requirements
 

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