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From: firstname.lastname@example.org (Allan Herriman)
Subject: Re: Line-powered EIA-232 interface
Date: Tue, 17 Dec 2002 04:44:52 GMT
Organization: Agilent Technologies
References: <email@example.com> <firstname.lastname@example.org>
NNTP-Posting-Date: Tue, 17 Dec 2002 04:44:52 +0000 (UTC)
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On Mon, 16 Dec 2002 23:14:41 +0100, Oliver Betz
>email@example.com (Allan Herriman) wrote:
>>You can make up the 'missing' rail with a charge pump converter IC
>>such as the '7660 (e.g. http://www.national.com/pf/LM/LMC7660.html ).
>>This sounds simple, but it may take some careful thought to avoid
>>latching up the charge pump in all the corner cases.
>Ack. And the data sheets don't say too much about 766x startup without
yes, that's why I said:
>> Put a diode from your laptop +3V rail to the '7660 +ve rail to avoid
>> startup problems.
>I looked at most data sheets and application notes, asked tech
>supports, but am still not 100% sure.
>Intersil: "a high value resistor to the LV pin ensures start-up". BTW:
>AN051.pdf is quite interesting.
>ON Semi "The only problem here is that the internal clock and switch
>drive section will not operate until some positive voltage has been
>generated. [...] or else the diode and resistor shown dotted in Figure
>10 can be used to force the internal regulator on." (1MOhm from LV to
>General Semiconductor (now Vishay): "R1 is added to ensure that
>doubling is not inhibited by a non-destructive latch-up at start-up.
>This condition can occur, since the ground pin (pin 3) is raised above
>the VIN pin (pin 8) during start-up." R1 is between pin 3 and GND and
>therefore increases noticeable the output resistance of the charge
>So there are two things to observe: 1. To power up the oscillator, one
>has to pull down the LV pin. 2. Pulling pin 8 below GND will result in
>latch-up. This could happen with loads between V+ and V-.
>Oliver Betz, Muenchen
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