PCA9685 with external drivers - Direct gate driving capability?

rainer-nxp — Wed, 26 Aug 2020 22:40:02 GMT

Hi,

I am working on a project where I would like to use PCA9685 to drive
power-mosfets (BUK9K25-40E or similar with ~800pF input capacitance).

However from the PCA9685 datasheet I cannot extract consistent information on
how to use the device with external drivers:

On page 35 (Chapter 10. Application design-in information) an example
schematic is shown with driver mosfet Gates directly attached to the PCA9685
However on page 2 it is stated that totem-pole outputs are able to "sink 25
mA and source 10 mA at 5 V"

I cannot find any details on how the 10mA source current is limited
(i.e. is this limited by the device internally, or do I have to add external
protection to prevent the PCA9685 from excessive gate charging current?)

This leads me to the design questions:

Do I need to add a Gate charge resistor between PCA9685 and the external
driver mosfet?
If yes which value should it have?

Re: PCA9685 with external drivers - Direct gate driving capability?

guoweisun — Thu, 27 Aug 2020 01:45:48 GMT

For example the 10mA source current limited by inside of IC.

You can test the drive waveform then decide to use the series resistor,if there is high over shoot on the waveform you can consider about 10Ω resistor in series.

topic Re: PCA9685 with external drivers - Direct gate driving capability? in Power Management

PCA9685 with external drivers - Direct gate driving capability?

Re: PCA9685 with external drivers - Direct gate driving capability?