Looking for a rail-to-rail input comparator - Page 1
Forum section: electronics / projects

author: Manx
author_rank: Contributor
timestamp: August 30, 2020, 06:40:48 pm
content: Could you recommend some reasonably cheap comparator (better yet, comparator family) that I could use instead of the LM393 family, but that would work with rail-to-rail inputs?

author: schmitt trigger
author_rank: Super Contributor
timestamp: August 30, 2020, 07:00:43 pm
content: Rail to rail inputs is one of the many selectable parameters, some of them conflicting.It includes max/min supply voltages, speed, totem pole or open collector outputs, strobing, power consumption, number of devices per IC package, package type and size, output drive capabilities, and of course the price.Some comparators have special features, like internal references or complementary outputs.The best is to go to the TI, Maxim, Analog, Onsemi and STMicro websites, look in the products section for comparators, and filter according to your requirements.For instance:https://www.ti.com/amplifier-circuit/comparators/overview.html

author: David Hess
author_rank: Super Contributor
timestamp: August 31, 2020, 02:57:52 am
content: How about the TLV3701/2/4?They are 16 volt, 36 microsecond, and push-pull output.

author: Alti
author_rank: Frequent Contributor
timestamp: September 02, 2020, 10:44:19 am
content: LM393 has bipolar PNP inputs with around 20nA biasing current. So if you bias inputs, it will accept rail2rail at a cost of 20nA current draw and higher offset voltage. Add a voltage divider so that when signal is at Vcc then input receives Vcc-1.2V.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 02, 2020, 12:29:14 pm
content: Right, what speed and supply voltage? Precision offset or no?Tim

author: Manx
author_rank: Contributor
timestamp: September 02, 2020, 05:39:04 pm
content: Thanks guys! I didn't find "rail-to-railness" as a search parameter at Mauser or Farnell, but after some manual sifting through I decided to go with MAX985 family, that seems to be a good pick for a quite universal comparator. There was also MCP6541/MPC6546 family, but they are slower.TLV3701 family is nice, thanks for the idea. Now I'll go with something faster, but I'll remember them when I'm focused on power consumption.@Alti, thanks for the out-of-the-box answer. It'll help me use up the LM393's I already have.

author: ledtester
author_rank: Super Contributor
timestamp: September 02, 2020, 07:01:17 pm
content: Quote from: Manx on August 30, 2020, 06:40:48 pmIf your inputs are near the top rail, how about using a voltage divider to reduce them?

author: David Hess
author_rank: Super Contributor
timestamp: September 03, 2020, 03:24:51 am
content: Quote from: Manx on September 02, 2020, 05:39:04 pmMy criteria was a higher supply voltage which presents a problem for comparators since they require a wide differential input voltage range which is incompatible with rail-to-rail inputs. The MAX985 is much faster but limited to 5 volt supplies rather than at least 15 volts for the TLV3701 family.Arguably however if you need a rail-to-rail input of more than 5 volts, then a different circuit topology should be used.