Hi, Thu, 23 Sep 2010 11:54:49 +0800, Adam Wang <[email protected]> : > The LM4550B needs at 4.2V(min.). That's why you chose 4.3V I think.
Yes. > Its VI = VO(typ) + 1 V, which means the VI needs 5.3V typically. The > input voltage if defined as a range of 4.75 ~ 5.25V on DC jack, so > this new idea 4.3V for LM4550 must not work reliable. No, I think it should work. The VI = VO(typ) + 1 V condition is only listed in the datasheet as the point at which some parameters of the device were characterized, but not as a requirement. The document "Technical review of low dropout voltage regulator operation and performance" by Texas Instruments [1] defines the dropout voltage as: "the input-to-output differential voltage at which the circuit ceases to regulate against further reductions in input voltage; this point occurs when the input voltage approaches the output voltage." Then the datasheet of the TPS76301 lists a typical dropout voltage of 300mV at 150mA (the LM4550 has a quiescent current of only 53mA) which is, I think, far enough from the 4.75V-4.3V = 450mV worst case so we don't have to worry too much about this. Anyway, to be 100% safe - let's add a 0 ohm resistor placeholder between the regulator's input and output. The board works without the extra regulation (only with a noticeable white noise in the line output) and this way we can easily bypass it if it is a source of more serious problems. Thanks for checking this! S. [1] http://www.ti.com/litv/pdf/slva072 _______________________________________________ http://lists.milkymist.org/listinfo.cgi/devel-milkymist.org IRC: #milkym...@freenode Webchat: www.milkymist.org/irc.html Wiki: www.milkymist.org/wiki
