When to use a voltage follower

Thread Starter

anishkgt

Joined Mar 21, 2017
547
Hello all,

My plan is to have two PCBs stacked 14mm apart connecting each other with an IDC connector. The top pcb will will have an atmega328 triggering 6 drivers driving each MOSFET. Is it necessary to have a voltage buffer in series with the atmega328 and the driver ? If yes would the MCP6L1 be ok or is a dedicated buffer such as the 74LVC1G07 be required ?
 

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MrChips

Joined Oct 2, 2009
23,929
You have an Atmel ATmega328 driving a driver driving a buffer driving a MOSFET.
Why do you think you need any of those components?
What are your concerns?
 

Thread Starter

anishkgt

Joined Mar 21, 2017
547
Why do you think you need any of those components?
The MOSFETs need to switch on fast because the project i plan for is a spot welder. The current to weld would come from the supercaps 2.7v 310F in a 3s2p configuration. So driving without a driver would not give the fastest switch on time.
What are your concerns?
Would there be any chance for a voltage drop. would all the drivers receive the signal equally.
 

MrChips

Joined Oct 2, 2009
23,929
The switching time will be determined by the capacitance at the MOSFET gate and the output impedance of the driver.
 

dl324

Joined Mar 30, 2015
12,919
clipimage.jpg

Why do you need all of the resistors on the gates? What are the diodes for?

You don't need a voltage follower. Unless the 6 MCP1416 exceed the drive capability of the ATmega328, you don't even need to buffer the output.
 

Thread Starter

anishkgt

Joined Mar 21, 2017
547
@MrChips Thank you. Based on those parameters i've chosen the driver and from the drivers datasheet the outputs are low-impedance

1592871496928.png
@dl324 The resistors will be blank, should i need to populate them to control the inrush current. I would just add one for each at first short the others. The MOSFETs would be acting as an ON-OFF switch.The schottky diodes are for a lower resistance path during turn-off.
 

Thread Starter

anishkgt

Joined Mar 21, 2017
547
This was the line that was a concern to me
The MOSFET driver input is a high-impedance, TTL/CMOS compatible input
So does that mean it is high-impedance but compatible and a buffer is not required?
 

Thread Starter

anishkgt

Joined Mar 21, 2017
547
SO when is it necessary to add a buffer. Thought it was done when the trace between two points on a pcb is long. Is it when the output is high-impedance ?
 
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