I guess I have a problem then! 8000uF cap is too costly for my low-cost product and I don't have 9V voltage rail. Actually, I have 8V rail but it's noisy like hell. Thanks for your help! Thomas ----- Original Message ----- From: "Richard Prosser" To: Sent: Thursday, August 30, 2001 5:50 PM Subject: Re: [EE]: Help! Data Flash corruption > Thomas > Lets see, you need 35mA at 2.7V(minimum) for 40mS. This corresponds to 95mW > for 40mS or 3.8mJ. > Allowing for 1V drop on the storage cap (5V to 4V) - enough for an LDO > regulator to easily maintain 2.7V on the output - then E=1/2C(Vh-Vl)^2 > or 3.8e-3 = 0.5 x C x (5-4) x (5-4) i.e. C=3.8e-3/(0.5 x 1) = 8mF > (8000uF) ! > > Something of a problem. > > If you could increase the supply voltage to the regulator to , say 9V, the > the cap would only need to be about 3.8e-3/(0.5 x 5 x 5) = 304uF, i.e. > your 470uF cap should be OK > > Or support the Flash from a supercap or in-board battery backup? > > Richard > > > > > > > > > > > > Richard, > > I use a simple transistor circuit to detect the voltage drop to shut down > to > MCU. However, the voltage drop down too fast and in some cases, it screws > up the flash if it's in a write operation. I use a separate regulator for > the flash. The input of the regulator is connected to 5V and with a 470uF > cap to ground. The output of the regulator is connected to 10uF cap. > Still, the 470uF cap can't supply enough energy. I checked out the specs, > and the flash consumes up to 35mA during the write operation. I need to > retain its power for at least 20ms, 40ms is refer... Guess I am stuck and > have to live with it :( > > Thomas > > > >From: Richard Prosser > >Reply-To: pic microcontroller discussion list > >To: PICLIST@MITVMA.MIT.EDU > >Subject: Re: [EE]: Help! Data Flash corruption > >Date: Fri, 31 Aug 2001 11:00:34 +1200 > > > >Thomas > >Presumably you are using a brownout detect of some sort to stop the > >processor as the volts die. We were having a similar problem (with a > >different Atmel chip) but fixed it by enabling the brownout detector & > >setting it to 4V. As the volts dropped the program wandered wherever it > >liked and often ended up corrupting the EEPROM. > >If the problem really is the supply dying during a write, then the only > fix > >is to make sure you have enough on-board capacity (caps or battery) to > hold > >the supply up until the EEPROM write is complete. > >Since the micro won't be drawing all of the 10mA (I guess) - can you > >separate the micro supply from the rest of the circuit using a diode and > >use a cap to hold the micro supply up until the write is compete? - You > may > >need to supply the circuit at 5.6 V and then have 2 diodes splitting the > >supplies to 5V for the micro & the "rest". > > > > > >Richard P > > > > > > > > > >Hello everyone, > > > >I am using a data flash (ATMEL 45DB041B) to store voice information. I > >often get data corruption (I think the table of contents screws up) when I > >power up and down the test board (I get data corruption about once every > >100 > >tries) > > > >Let say the MCU sends out a "program a page" command, and the data flash > >starts to program a page (it takes about 10ms to program one page) and > >during the time where the data flash is being programmed , the unit is > >powered down. Data corruption occurs!!! > > > >Is there any way to overcome this problem? Any work-around? I tried to > >put > >the big cap at the data flash supply to retain its power (for 10ms), but > >during the write operation, the data flash consumes lots of current (20 > >mA), > >so it's too much for the cap. > > > >Thank you in advance! > >Thomas > > > > > >_________________________________________________________________ > >Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp > > > >-- > >http://www.piclist.com hint: PICList Posts must start with ONE topic: > >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > >-- > >http://www.piclist.com hint: PICList Posts must start with ONE topic: > >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > > > _________________________________________________________________ > Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads