Question on Lead Acid Battery Recharger Datasheet - Electronic Circuits Projects Diagrams Free

DigiTan · 15th December 2005, 10:28 PM

I'm looking at the datasheet for a UC3906 lead-acid battery recharger, and I'm trying to make sence of something I saw in one of the figures.

The charger needs several external resistors for calibration. I'm ready to purchase these resistors, but first, the datasheet says I need to use the figure below to find the resistor values. The problem is that they are all dependent on some figure "Id" that isn't described in the documents. Also, they suggest setting it to 50A to 100A, which clearly seems excessive. Perhaps they meant mA or uA? I don't think it's a misprint because this datasheet revivsion has stood for 2 years.

DigiTan · 15th December 2005, 10:51 PM

Wow, I don't know whether to call this good or bad timing, but I just found a web article involving the UC3906, and the author suggested these are µA ranges. I don't know wheter I'm witnessing a PDF reader error or an actual misprint, but I definately dodged a bullet here.

I want to have this charger built within the week, so if I discover anything new, I'll update everyone. If anyone has any other corrections or comments, please reply.

ljcox · 15th December 2005, 10:53 PM

It is definitely not Amps.

The Id is the current through the RA RB & RC voltage divider. The usual rule of thumb is that the current through a voltage divider should be at least 10 times the current drawn from it.

Looking at the data sheet, the input bias currents are <1 uA. So I suspect that they mean uA. Milliamp would be unnecessarily excessive.

So Id = Battery Voltage / (RA + RB + RC).

nsklavos · 16th December 2005, 01:03 AM

Definitely microamps (uA). Read it from an old Unitrode Databook. TI's dataseet is incorrect.

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15th December 2005, 10:28 PM	(permalink)
DigiTan	Question on Lead Acid Battery Recharger Datasheet I'm looking at the datasheet for a UC3906 lead-acid battery recharger, and I'm trying to make sence of something I saw in one of the figures. The charger needs several external resistors for calibration. I'm ready to purchase these resistors, but first, the datasheet says I need to use the figure below to find the resistor values. The problem is that they are all dependent on some figure "Id" that isn't described in the documents. Also, they suggest setting it to 50A to 100A, which clearly seems excessive. Perhaps they meant mA or uA? I don't think it's a misprint because this datasheet revivsion has stood for 2 years. __________________ The most-hated young engineer in America. * AVR Projects * Robot War: TI * About

15th December 2005, 10:51 PM	(permalink)
DigiTan	Wow, I don't know whether to call this good or bad timing, but I just found a web article involving the UC3906, and the author suggested these are µA ranges. I don't know wheter I'm witnessing a PDF reader error or an actual misprint, but I definately dodged a bullet here. I want to have this charger built within the week, so if I discover anything new, I'll update everyone. If anyone has any other corrections or comments, please reply. __________________ The most-hated young engineer in America. * AVR Projects * Robot War: TI * About

15th December 2005, 10:53 PM	(permalink)
ljcox	It is definitely not Amps. The Id is the current through the RA RB & RC voltage divider. The usual rule of thumb is that the current through a voltage divider should be at least 10 times the current drawn from it. Looking at the data sheet, the input bias currents are <1 uA. So I suspect that they mean uA. Milliamp would be unnecessarily excessive. So Id = Battery Voltage / (RA + RB + RC). __________________ Len

16th December 2005, 01:03 AM	(permalink)
nsklavos	Definitely microamps (uA). Read it from an old Unitrode Databook. TI's dataseet is incorrect.