From: Bob Blick <bobblick@outlook.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 2 Sep 2020 13:25:33 -0700
Subject: Re: [EE] High Side LCD Backlight Control
Thread-Topic: [EE] High Side LCD Backlight Control
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Hi Josh,
I have used the AO3401A without a gate resistor when doing low-speed switch=
ing. It has a fairly high amount of capacitance so if you were going to be =
switching inductive loads I would use 47 or 100 ohms just to soften the edg=
es from ringing and isolate the microcontroller a bit. The output resistanc=
e of most 3.3 volt microcontrollers is more than a hundred ohms anyway so i=
t's hardly worth it, switching speed is going to be at least a few microsec=
onds already. But driving LED backlights isn't likely to present any weirdn=
ess, just use the raw MOSFET directly. If you want to do dimming, keep the =
PWM frequency under a few KHz and you'll be fine. I usually use 1KHz driven=
 from the same timebase as the system tick.
Friendly regards, Bob
________________________________________
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Josh K=
offman=20
Sent: Wednesday, September 2, 2020 12:49 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] High Side LCD Backlight Control

On Sat, Aug 29, 2020 at 8:50 PM Bob Blick  wrote:
> Simplest is a P-channel Mosfet, recommend something from Alpha and Omega =
Semiconductor, part number AO3-something.
> Cheapest solution is probably a PNP transistor with a base resistor.
> Either will be fine. Hard to say which I'd choose. Both will invert, so 0=
 is ON.


Hi Bob,

I'm leaning towards a P-channel MOSFET. I had forgotten about A&O, I
will check out their offerings!

Would I need a gate resistor? I have very little experience with
P-channel parts.

Thanks,

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
        -Douglas Adams


--=20
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