accuracy of BCV62
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From: Michael Robinson on 26 Mar 2010 11:08 On page 4 of this datasheet http://www.nxp.com/documents/data_sheet/BCV62.pdf the manufacuterer gives 0.7 to 1.3 for Ic1/Ic2. Other manufacturers' datasheets use the same number. How many sigmas away from the mean the 30% accuracy statistic is makes a huge difference in the attractiveness of this current mirror as a part I want to buy. But the datasheets don't give that kind of information. Have you used these current mirrors and can give me an idea what kind of accuracy could I expect from the actual physical parts?
From: Hammy on 26 Mar 2010 11:25 On Fri, 26 Mar 2010 11:08:24 -0400, "Michael Robinson" <nospam(a)billburg.com> wrote: >On page 4 of this datasheet >http://www.nxp.com/documents/data_sheet/BCV62.pdf >the manufacuterer gives 0.7 to 1.3 for Ic1/Ic2. >Other manufacturers' datasheets use the same number. >How many sigmas away from the mean the 30% accuracy statistic is makes a >huge difference in the attractiveness of this current mirror as a part I >want to buy. But the datasheets don't give that kind of information. >Have you used these current mirrors and can give me an idea what kind of >accuracy could I expect from the actual physical parts? > Have you seen diodes matched pnpn's? http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=DMMT3906W-FDICT-ND http://www.diodes.com/_files/news/DMMT3906W_DMMT3904W.pdf All diodes matched pairs http://www.diodes.com/products/catalog/list.php?parent-id=28
From: John Larkin on 26 Mar 2010 11:28 On Fri, 26 Mar 2010 11:08:24 -0400, "Michael Robinson" <nospam(a)billburg.com> wrote: >On page 4 of this datasheet >http://www.nxp.com/documents/data_sheet/BCV62.pdf >the manufacuterer gives 0.7 to 1.3 for Ic1/Ic2. >Other manufacturers' datasheets use the same number. >How many sigmas away from the mean the 30% accuracy statistic is makes a >huge difference in the attractiveness of this current mirror as a part I >want to buy. But the datasheets don't give that kind of information. >Have you used these current mirrors and can give me an idea what kind of >accuracy could I expect from the actual physical parts? > The test circuits, fig 2 and 3, don't make sense. And transistors are "Q" not "TR". Emitter resistors will improve mirror accuracy. Horrible data sheet. Are these monolithic? Fig 4 looks like some sort of thermal runaway limit, so they're probably not. Here's a UPA800 dual transistor, thermal image with one transistor dissipating 80 mW. The other transistor is nowhere near the same temp. ftp://jjlarkin.lmi.net/UPA800_80mW_one-side.jpg Such "dual" transistors aren't a lot better than two separate beta-graded transistors. John
From: Hammy on 26 Mar 2010 11:31 On Fri, 26 Mar 2010 11:25:56 -0400, Hammy <spam(a)spam.com> wrote: >On Fri, 26 Mar 2010 11:08:24 -0400, "Michael Robinson" ><nospam(a)billburg.com> wrote: > >>On page 4 of this datasheet >>http://www.nxp.com/documents/data_sheet/BCV62.pdf >>the manufacuterer gives 0.7 to 1.3 for Ic1/Ic2. >>Other manufacturers' datasheets use the same number. >>How many sigmas away from the mean the 30% accuracy statistic is makes a >>huge difference in the attractiveness of this current mirror as a part I >>want to buy. But the datasheets don't give that kind of information. >>Have you used these current mirrors and can give me an idea what kind of >>accuracy could I expect from the actual physical parts? >> >Have you seen diodes matched pnpn's? > >http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=DMMT3906W-FDICT-ND > >http://www.diodes.com/_files/news/DMMT3906W_DMMT3904W.pdf > >All diodes matched pairs > >http://www.diodes.com/products/catalog/list.php?parent-id=28 From thier website. "Built with adjacent die from a single wafer: DC Current Gain, hFE, VCE(sat), VBE(sat) are matched to a 2% maximum tolerance." Which is better then the BCV62.
From: John Larkin on 26 Mar 2010 11:35
On Fri, 26 Mar 2010 11:31:17 -0400, Hammy <spam(a)spam.com> wrote: >On Fri, 26 Mar 2010 11:25:56 -0400, Hammy <spam(a)spam.com> wrote: > >>On Fri, 26 Mar 2010 11:08:24 -0400, "Michael Robinson" >><nospam(a)billburg.com> wrote: >> >>>On page 4 of this datasheet >>>http://www.nxp.com/documents/data_sheet/BCV62.pdf >>>the manufacuterer gives 0.7 to 1.3 for Ic1/Ic2. >>>Other manufacturers' datasheets use the same number. >>>How many sigmas away from the mean the 30% accuracy statistic is makes a >>>huge difference in the attractiveness of this current mirror as a part I >>>want to buy. But the datasheets don't give that kind of information. >>>Have you used these current mirrors and can give me an idea what kind of >>>accuracy could I expect from the actual physical parts? >>> >>Have you seen diodes matched pnpn's? >> >>http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=DMMT3906W-FDICT-ND >> >>http://www.diodes.com/_files/news/DMMT3906W_DMMT3904W.pdf >> >>All diodes matched pairs >> >>http://www.diodes.com/products/catalog/list.php?parent-id=28 > >From thier website. > >"Built with adjacent die from a single wafer: DC Current Gain, hFE, >VCE(sat), VBE(sat) are matched to a 2% maximum tolerance." > >Which is better then the BCV62. If the thermal situation is poor, as it almost always is for separate die, the Vbe matching is only good at very low currents. John |