Question: L200 - delta V(i-o) "Dropout Voltage" (Absolute Maximum Ratings) - Page 1
Forum section: electronics / projects

author: robert67
author_rank: Contributor
timestamp: June 13, 2017, 08:06:20 am
content: Hi,in the L200 datasheet "Absolute Maximum Ratings" section there is adelta Vi-oDropout Voltage 32Vlisted.My interpretation of this: The voltage drop between input (pin 1) and output (pin 5) shall never exceed 32V.Example:If the minimal output voltage is 2.85V (reference pin 4 connected to output pin 5), then the absolute maximum input voltage is 34.85V (2.85V + 32V).Assuming a ripple of 5V (max. 34.85V, min. 29.85V) at a given current on the input voltage, ...... and a minimum dropout voltage of 2 V across the L200 between input (pin 1) and output (pin 5) ...... then the maximum achievable regulated output voltage (with a voltage divider between pins 4/5) is 27.85V (29.85V - 2V).However, there are designs using the L200 out there that seem to violate that absolute maximum rating, at least by a few volts.So my question is: How "serious" is that absolute maximum rating? Or is my interpretation wrong?

author: Paul Price
author_rank: Super Contributor
timestamp: June 13, 2017, 09:31:47 pm
content: Dropout voltage is always the minimal input to output voltage that a regulator will operate remaining in spec.The spec shown near the top of the first page of ST L200 datasheet is Abs. Max = 32V. This is a typo and should be read as 3.2V.

author: Zero999
author_rank: Super Contributor
timestamp: June 13, 2017, 09:47:19 pm
content: What data sheet are you reading? Like any other linear regulator, the drop-out voltage depends on the junction temperature and current.http://www.st.com/content/ccc/resource/technical/document/datasheet/04/2c/9f/b5/65/15/49/ac/CD00000053.pdf/files/CD00000053.pdf/jcr:content/translations/en.CD00000053.pdf

author: robert67
author_rank: Contributor
timestamp: June 14, 2017, 05:16:52 am
content: Quote from: Paul Price on June 13, 2017, 09:31:47 pmThat explains it! A typo in the datasheet! Though I knew what the "dropout voltage" of a regulator normally is, I was convinced that they (ST) must mean something else. I couldn't fathom a "dropout voltage" of 32V.Thank you very much!

author: robert67
author_rank: Contributor
timestamp: June 14, 2017, 05:32:52 am
content: Quote from: Hero999 on June 13, 2017, 09:47:19 pmI'm reading exactly the datasheet you've linked. And on the very first page, under "Absolute Maximum Ratings", it says "Dropout Voltage" 32V!Either that's not the "like any other" "Dropout Voltage", which I initially (and falsely) assumed (otherwise the maximum output voltage of an L200 would be 8V, with its maximum input voltage being 40V).Or it's simply a typo in the datasheet (which Paul Price pointed out so nicely in the first reply to my post - thank you again Paul). The "like any other" "Dropout Voltage" in fact being 3.2V.

author: Zero999
author_rank: Super Contributor
timestamp: June 14, 2017, 06:32:23 am
content: Quote from: robert67 on June 14, 2017, 05:32:52 amYes, it's a typo. I didn't even notice it!

author: robert67
author_rank: Contributor
timestamp: June 14, 2017, 11:32:27 am
content: Quote from: Hero999 on June 14, 2017, 06:32:23 amDon't worryI didn't realize that either, and was going down the rabbit hole redefining "Dropout Voltage"