Need substitute for Microchip MCP1755 with higher output cur [Solution: MCP1826] - Page 1
Forum section: electronics / projects

author: cgroen
author_rank: Unknown
timestamp: April 26, 2017, 10:51:47 am
content: I know this is a long shot, but I'm trying anyway (as I'm constantly amazed about the knowledge accumulated on this forum)I have a design with a MCP1755T-3302E/DC in SOT223-5 (http://ww1.microchip.com/downloads/en/DeviceDoc/25160A.pdf).For some reason I mis-calculated the total current consumption of the design (I changed the CPU and few other things between respins) and the result is that the 300 mA the MCP1755 can deliver is a little on the low, a 500 mA device would be a better match (I have 433 MHz module, Bluetooth and a 320x240 color TFT display).I need the SHDN input on the device (battery powered device, single LiIon cell).Do any of you know a device that is in the same SOT223-5 house, pin compatible with the MCP1755 and at the same time capable of more than the 300 mA the MCP1755 is rated for ?Crossing my fingers....

author: ebclr
author_rank: Super Contributor
timestamp: April 26, 2017, 11:12:25 am
content: I didn't check the pinouthttp://www.mouser.com/ds/2/268/mic5219-779135.pdf

author: cgroen
author_rank: Unknown
timestamp: April 26, 2017, 11:14:56 am
content: Thanks ebclr,it wont work though, it is unfortunately not a SOT223-5 house. Thanks for trying!

author: Zero999
author_rank: Super Contributor
timestamp: April 26, 2017, 11:20:23 am
content: How about continuing with the MCP1755 but modifying it?Does the device connected to the regulator always draw a minimum load current?If so, you might be able to add a bypass resistor, between MCP1755's input and output pins the, to divert current round it. This also assumes that the resistor can pass the required current over the range of input voltages, i.e. it won't be too little at low voltages or too much at high voltages. A constant current source could be another option.What's the minimum drop-out voltage you require? If the circuit can stand an extra 0.7V or so of voltage drop, then how about a PNP pass transistor, as is commonly used with other linear regulators, such as the LM317?Both of the above options could be bodged onto an existing board, for prototyping or low volume applications.

author: ebclr
author_rank: Super Contributor
timestamp: April 26, 2017, 11:26:59 am
content: Try this onehttp://www.ti.com/lit/ds/symlink/lp38693.pdf

author: Zero999
author_rank: Super Contributor
timestamp: April 26, 2017, 11:29:19 am
content: Found it!MCP1826http://ww1.microchip.com/downloads/en/DeviceDoc/22057B.pdfYou could also try the LP3961 but would need to leave pin 5 unconnected.http://www.ti.com/lit/ds/symlink/lp3964.pdf

author: cgroen
author_rank: Unknown
timestamp: April 26, 2017, 11:38:41 am
content: Quote from: Hero999 on April 26, 2017, 11:29:19 amYou and the MCP1826 seems to save my dayI will order a few and see if the does the trick! Thanks for all replies guys, this just confirms the power of this forum

author: MagicSmoker
author_rank: Super Contributor
timestamp: April 26, 2017, 11:49:01 am
content: Mind the thermal performance, OP... the typical SOT223 package is good for 0.5W of dissipation when the minimum size pad for the tab is used. Check the total R_theta from junction to ambient and the size of the pad required to achieve it before you settle on merely swapping out a 300mA regulator for a 1A version. Personally, I would move up to a DPAK package if I needed 500mA from a 3.3V LDO regulator that was supplied by a 5V rail.

author: cgroen
author_rank: Unknown
timestamp: April 26, 2017, 12:12:04 pm
content: Quote from: MagicSmoker on April 26, 2017, 11:49:01 amYup, the consumption is not continuous so the thermal should not be an issue (thanks for mentioning it!)

author: cgroen
author_rank: Unknown
timestamp: April 27, 2017, 01:24:55 pm
content: Took delivery of a bunch of MCP1826 today (Farnell) and they work perfect in my design !!!@Hero999, thanks a lot for pointing me to this device!!!