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Mega644 Brown Out Detector Problem

2011-09-15 by Phillip Vogel

I'm having what I hope is a minor problem. My circuit contains a mega644p powered by a lithium battery through a 3.3V regulator. There is a 12MHz crystal, and the CKDIV8 fuse is set, resulting in a clock speed of 1.5MHz.

If I set the brown out detector to 2.7V, the chip never comes out of reset. It starts up OK if I set the BOD to off or 1.8V, but not 2.7V. I have checked the supply voltage, and it is, indeed, 3.30V.

What am I missing here?

Re: Mega644 Brown Out Detector Problem

2011-09-15 by greggy

The regulator probably needs 1 - 1.5 volts head room, which your battery is not supplying. Just remove the regulator. Or use two batteries in series to push the voltage up.

--- In AVR-Chat@yahoogroups.com, Phillip Vogel <phillip@...> wrote:

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>
> 
> I'm having what I hope is a minor problem. My circuit contains a mega644p powered by a lithium battery through a 3.3V regulator. There is a 12MHz crystal, and the CKDIV8 fuse is set, resulting in a clock speed of 1.5MHz.
> 
> If I set the brown out detector to 2.7V, the chip never comes out of reset. It starts up OK if I set the BOD to off or 1.8V, but not 2.7V. I have checked the supply voltage, and it is, indeed, 3.30V.
> 
> What am I missing here?
>

RE: [AVR-Chat] Re: Mega644 Brown Out Detector Problem

2011-09-15 by Phillip Vogel

Nope. This is a low dropout regulator, and there is plenty of battery voltage. The supply voltage to the chip IS (not "is supposed to be") 3.30V.

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> -----Original Message-----
> From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
> Behalf Of greggy
> Sent: Thursday, September 15, 2011 3:36 PM
> To: AVR-Chat@yahoogroups.com
> Subject: [AVR-Chat] Re: Mega644 Brown Out Detector Problem
> 
> The regulator probably needs 1 - 1.5 volts head room, which your
> battery is not supplying. Just remove the regulator. Or use two
> batteries in series to push the voltage up.
> 
> --- In AVR-Chat@yahoogroups.com, Phillip Vogel <phillip@...> wrote:
> >
> >
> > I'm having what I hope is a minor problem. My circuit contains a
> mega644p powered by a lithium battery through a 3.3V regulator. There
> is a 12MHz crystal, and the CKDIV8 fuse is set, resulting in a clock
> speed of 1.5MHz.
> >
> > If I set the brown out detector to 2.7V, the chip never comes out of
> reset. It starts up OK if I set the BOD to off or 1.8V, but not 2.7V. I
> have checked the supply voltage, and it is, indeed, 3.30V.
> >
> > What am I missing here?
> >
> 
> 
> 
> 
> ------------------------------------
> 
> Yahoo! Groups Links
> 
> 
>

Re: [AVR-Chat] Re: Mega644 Brown Out Detector Problem

2011-09-16 by R E Purcella

What is your voltage ref set to?

rep

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On 9/15/2011 12:46 PM, Phillip Vogel wrote:
>
> Nope. This is a low dropout regulator, and there is plenty of battery 
> voltage. The supply voltage to the chip IS (not "is supposed to be") 
> 3.30V.
>
>
> > -----Original Message-----
> > From: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> 
> [mailto:AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com>] On
> > Behalf Of greggy
> > Sent: Thursday, September 15, 2011 3:36 PM
> > To: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com>
> > Subject: [AVR-Chat] Re: Mega644 Brown Out Detector Problem
> >
> > The regulator probably needs 1 - 1.5 volts head room, which your
> > battery is not supplying. Just remove the regulator. Or use two
> > batteries in series to push the voltage up.
> >
> > --- In AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com>, 
> Phillip Vogel <phillip@...> wrote:
> > >
> > >
> > > I'm having what I hope is a minor problem. My circuit contains a
> > mega644p powered by a lithium battery through a 3.3V regulator. There
> > is a 12MHz crystal, and the CKDIV8 fuse is set, resulting in a clock
> > speed of 1.5MHz.
> > >
> > > If I set the brown out detector to 2.7V, the chip never comes out of
> > reset. It starts up OK if I set the BOD to off or 1.8V, but not 2.7V. I
> > have checked the supply voltage, and it is, indeed, 3.30V.
> > >
> > > What am I missing here?
> > >
> >
> >
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
>
>

RE: [AVR-Chat] Re: Mega644 Brown Out Detector Problem

2011-09-16 by M W

If the LDO Regulator isn't bypassed properly it can oscillate, that could cause the Brown Out Reset to be firing when it drops, possibly? (If you don't bypass properly, it will bite you, it's bitten all of us probably LOL)

Long day so that's all that I can think of ATM.

  Mark

--- On Thu, 9/15/11, Phillip Vogel <phillip@bartal.com> wrote:

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> From: Phillip Vogel <phillip@bartal.com>
> Subject: RE: [AVR-Chat] Re: Mega644 Brown Out Detector Problem
> To: "AVR-Chat@yahoogroups.com" <AVR-Chat@yahoogroups.com>
> Date: Thursday, September 15, 2011, 12:46 PM
> Nope. This is a low dropout
> regulator, and there is plenty of battery voltage. The
> supply voltage to the chip IS (not "is supposed to be")
> 3.30V.
> 
> > -----Original Message-----
> > From: AVR-Chat@yahoogroups.com
> [mailto:AVR-Chat@yahoogroups.com]
> On
> > Behalf Of greggy
> > Sent: Thursday, September 15, 2011 3:36 PM
> > To: AVR-Chat@yahoogroups.com
> > Subject: [AVR-Chat] Re: Mega644 Brown Out Detector
> Problem
> > 
> > The regulator probably needs 1 - 1.5 volts head room,
> which your
> > battery is not supplying. Just remove the regulator.
> Or use two
> > batteries in series to push the voltage up.
> > 
> > --- In AVR-Chat@yahoogroups.com,
> Phillip Vogel <phillip@...> wrote:
> > >
> > > I'm having what I hope is a minor problem. My
> circuit contains a
> > mega644p powered by a lithium battery through a 3.3V
> regulator. There
> > is a 12MHz crystal, and the CKDIV8 fuse is set,
> resulting in a clock
> > speed of 1.5MHz.
> > >
> > > If I set the brown out detector to 2.7V, the chip
> never comes out of
> > reset. It starts up OK if I set the BOD to off or
> 1.8V, but not 2.7V. I
> > have checked the supply voltage, and it is, indeed,
> 3.30V.
> > >
> > > What am I missing here?