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I finally have one of Leon's lpc210x proto boards assembled. The problem is the MAX3232 runs warm and seems to be drawing 150mA or so--it varies a bit. The lpc2106 runs at ambient and has detectable 10MHz on its clock pins. Removing the MAX3232 from the board causes it to use very little current ~10mAh, so I'm assuming the CPU is okay. Is there some common failure mode these things experience? I'm pretty sure there was no reverse voltage, etc. Could a poorly connected cap do this? I *really* want to talk to this thing, but if the serial interface won't work.... Cheers, David |
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MAX3232 problems?
Started by ●January 7, 2004
Reply by ●January 7, 20042004-01-07
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Hello David, Do the CAPS have the right polarity ? Pay attention: Pin 6 is the - side of the CAP, GND this time the '+' side. Same thing for Pin 2: - side to VCC 3.3 and + side to Pin 2. But usually when something above is wrong, the CAPS go hops (really, i saw tantals burning...). Have you used 3.3V as supply voltage for the MAX and the CAPS ? But i had a look at Maxim website and MAX3232 can also be driven by 5V. So this is not a problem. The RS232 and TTL side is not exchanged ? Sorry, Martin ----- Original Message ----- From: "David Willmore" <> To: <> Sent: Wednesday, January 07, 2004 10:43 PM Subject: [lpc2100] MAX3232 problems? > > I finally have one of Leon's lpc210x proto boards assembled. > The problem is the MAX3232 runs warm and seems to be drawing > 150mA or so--it varies a bit. > > The lpc2106 runs at ambient and has detectable 10MHz on its > clock pins. Removing the MAX3232 from the board causes it > to use very little current ~10mAh, so I'm assuming the CPU > is okay. > > Is there some common failure mode these things experience? > I'm pretty sure there was no reverse voltage, etc. Could > a poorly connected cap do this? > > I *really* want to talk to this thing, but if the serial > interface won't work.... > > Cheers, > David > |
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Reply by ●January 7, 20042004-01-07
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----- Original Message ----- From: "David Willmore" <> To: <> Sent: Wednesday, January 07, 2004 9:43 PM Subject: [lpc2100] MAX3232 problems? > > I finally have one of Leon's lpc210x proto boards assembled. > The problem is the MAX3232 runs warm and seems to be drawing > 150mA or so--it varies a bit. > > The lpc2106 runs at ambient and has detectable 10MHz on its > clock pins. Removing the MAX3232 from the board causes it > to use very little current ~10mAh, so I'm assuming the CPU > is okay. > > Is there some common failure mode these things experience? > I'm pretty sure there was no reverse voltage, etc. Could > a poorly connected cap do this? > > I *really* want to talk to this thing, but if the serial > interface won't work.... It sounds as if the MAX3232 has failed, it shouldn't take anything like that amount of current and shouldn't be warm. Many years ago I had quite frequent failures of the earlier version of this type of chip, caused by connecting the host machine to my board whilst the host was powered up. The current chips have ESD protection and seem a lot more robust. Check the voltages on the charge pump capacitors, if they are wrong (IIRC they should be about +/- 5V and +/- 12V) it won't work. Make sure you haven't got any shorts. Have you tried a new chip? Leon -- Leon Heller, G1HSM Email: My low-cost Philips LPC210x ARM development system: http://webspace.webring.com/people/jl/leon_heller//lpc2104.html |
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Reply by ●January 7, 20042004-01-07
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Hello, Leon. > It sounds as if the MAX3232 has failed, it shouldn't take anything like that > amount of current and shouldn't be warm. Many years ago I had quite frequent > failures of the earlier version of this type of chip, caused by connecting > the host machine to my board whilst the host was powered up. The current > chips have ESD protection and seem a lot more robust. Are you talking about the difference between the MAX3232 and MAX3232E kind of difference? > Check the voltages on the charge pump capacitors, if they are wrong (IIRC > they should be about +/- 5V and +/- 12V) it won't work. Make sure you > haven't got any shorts. Have you tried a new chip? They are off. They're more like 2.7V and 5.5V and -5.1V. I'll try a new chip next. If this were socketed, I could replace it more easily. ;) Cheers, David |
Reply by ●January 7, 20042004-01-07
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Is it also getting hot, when you don't have a serial cable connected
? TX <-> RX exchanged ? BTW: using a MAX-232 on my board, it is running for hours, is not even a bit hot. ----- Original Message ----- From: "David Willmore" <> To: <> Sent: Wednesday, January 07, 2004 11:15 PM Subject: Re: [lpc2100] MAX3232 problems? > > Do the CAPS have the right polarity ? > > Pay attention: Pin 6 is the - side of the CAP, GND this time the '+' side. > > Same thing for Pin 2: - side to VCC 3.3 and + side to Pin 2. > > Used ceramic caps. Thought they were too small, so I replaced them with > 4.7uF tants--which I was very sure to follow the data sheet and get the > polarity right. So, that's probably not it. > > The datasheet shows the V+ cap going to ground on the - side, but Leon's > board has it going to Vcc. That shouldn't make a difference, but it's > a little difference that I noticed. > > > But usually when something above is wrong, the CAPS go hops (really, i saw > > tantals burning...). > > They didn't do that, so one thing went right. Ever seen a 'lytic go? It's > like confetti. :) > > > Have you used 3.3V as supply voltage for the MAX and the CAPS ? But i had a > > look at Maxim website and MAX3232 can also be driven by 5V. So this is not a > > problem. > > It's running from the 3.3V supply on the board. > > > The RS232 and TTL side is not exchanged ? > > Uhhh, didn't look like it. Take a look at the board layout on Leon's website > for verification? > > Cheers, > David > |
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Reply by ●January 7, 20042004-01-07
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----- Original Message ----- From: "David Willmore" <> To: <> Sent: Wednesday, January 07, 2004 10:11 PM Subject: Re: [lpc2100] MAX3232 problems? > Hello, Leon. > > > It sounds as if the MAX3232 has failed, it shouldn't take anything like that > > amount of current and shouldn't be warm. Many years ago I had quite frequent > > failures of the earlier version of this type of chip, caused by connecting > > the host machine to my board whilst the host was powered up. The current > > chips have ESD protection and seem a lot more robust. > > Are you talking about the difference between the MAX3232 and MAX3232E kind of > difference? No, I'm talking about the original MAX232, 20 years ago. 8-) > > > Check the voltages on the charge pump capacitors, if they are wrong (IIRC > > they should be about +/- 5V and +/- 12V) it won't work. Make sure you > > haven't got any shorts. Have you tried a new chip? > > They are off. They're more like 2.7V and 5.5V and -5.1V. 2.7 V is definitely wrong. Leon -- Leon Heller, G1HSM Email: My low-cost Philips LPC210x ARM development system: http://webspace.webring.com/people/jl/leon_heller//lpc2104.html |
Reply by ●January 7, 20042004-01-07
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> Do the CAPS have the right polarity ? > Pay attention: Pin 6 is the - side of the CAP, GND this time the '+' side. > Same thing for Pin 2: - side to VCC 3.3 and + side to Pin 2. Used ceramic caps. Thought they were too small, so I replaced them with 4.7uF tants--which I was very sure to follow the data sheet and get the polarity right. So, that's probably not it. The datasheet shows the V+ cap going to ground on the - side, but Leon's board has it going to Vcc. That shouldn't make a difference, but it's a little difference that I noticed. > But usually when something above is wrong, the CAPS go hops (really, i saw > tantals burning...). They didn't do that, so one thing went right. Ever seen a 'lytic go? It's like confetti. :) > Have you used 3.3V as supply voltage for the MAX and the CAPS ? But i had a > look at Maxim website and MAX3232 can also be driven by 5V. So this is not a > problem. It's running from the 3.3V supply on the board. > The RS232 and TTL side is not exchanged ? Uhhh, didn't look like it. Take a look at the board layout on Leon's website for verification? Cheers, David |
Reply by ●January 7, 20042004-01-07
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----- Original Message ----- From: "David Willmore" <> To: <> Sent: Wednesday, January 07, 2004 10:15 PM Subject: Re: [lpc2100] MAX3232 problems? > > Do the CAPS have the right polarity ? > > Pay attention: Pin 6 is the - side of the CAP, GND this time the '+' side. > > Same thing for Pin 2: - side to VCC 3.3 and + side to Pin 2. > > Used ceramic caps. Thought they were too small, so I replaced them with > 4.7uF tants--which I was very sure to follow the data sheet and get the > polarity right. So, that's probably not it. > > The datasheet shows the V+ cap going to ground on the - side, but Leon's > board has it going to Vcc. That shouldn't make a difference, but it's > a little difference that I noticed. Oops! You are right. It could cause a problem with a polarised cap. Try putting it the other way round. I'll correct the schematic and fix the problem if I get some more boards made. I'll modify any more boards I send out. 100 nF ceramic caps are really all that is needed. The older MAX232 needs 1 uF. Leon -- Leon Heller, G1HSM Email: My low-cost Philips LPC210x ARM development system: http://webspace.webring.com/people/jl/leon_heller//lpc2104.html |
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Reply by ●January 7, 20042004-01-07
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> Is it also getting hot, when you don't have a serial cable
connected ? > TX <-> RX exchanged ? Even with no cable. That's how I started. :( > BTW: using a MAX-232 on my board, it is running for hours, is not even a bit > hot. That's what it's supposed to be like. :( Cheers, David |
Reply by ●January 7, 20042004-01-07
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> Oops! You are right. It could cause a problem with a polarised cap.
Try > putting it the other way round. > > I'll correct the schematic and fix the problem if I get some more boards > made. I'll modify > any more boards I send out. > > 100 nF ceramic caps are really all that is needed. The older MAX232 needs 1 > uF. I put in a 100nF chip cap for the problematic V+ cap and put in a new MAX3232. No joy. Same results. 150mA current draw and a warm chip. Could both of my chips be bad? I've never had this bad of luck since I put a chip in backwards. PICs hate that. I've got more coming in a few days. Maybe I'll proto a good old MAX232 and trust the tolerance of the lpc2106. :) Cheers, David |
