CZ3-AG2 Over Current Detection


Datasheet available at

As per section 10.5 of the manual, a voltage of 1.242V on Ref1 should enable over current protection at 10A. Let’s assume Rocd @ 1K and Clocd at 1000pF which gives the default Trsocd of 5.5uS

I am /completely/ failing to understand where Ref2 fits into the picture and/or diagram.

The datasheet explicitly mentions Ref1 and Ref2 having to separate functions as per the pin layouts (Section 6), and the example circuit provided in Section 11 also indicates separate values for Ref1 and Ref2. As does Section 10.5 for that matter.

Section 10.4 makes no mention of Ref1 and/or Ref2 at all.

Section 10.5 also states that valid values for Ref2 is between 17.5A and 35A (Ref1 is 7.0A to 17.5A), yet, the maximum current the IC can read, is 14A according to the datasheet?

Can someone please clarify Ref2 and the reference to 17.5 to 35A in the datasheets? My intention is to have OCD enabled at 10A

Many thanks,

Welcome to the forum.

This data sheet is particularly difficult to interpret due to what appears to be a low quality Japanese to English translation.

This chip has three functions:

The first two are independent overcurrent outputs (OCD1 & OCD2) controlled by two separate reference voltages (Ref1 & Ref2). This allows you to have two different overcurrent detection values for the one monitored power line if you want.
Since you only want to use one trip point, you need to connect OCD2 and Ref2 to VSS per the last sentence in section 10.5.

The third function is to provide a voltage output proportional to current for measurement applications.

That’s because it describes only the response time which is independent of the magnitude of the trip points set by Ref1/Ref2

Sections 2 and 8 say, Maximum Primary Current : 50Arms
Section 9 says +/-14A is the Linear Sensing Range
I read that to mean the Vout curve will not be linear for values > +/-14A but you can use this for up to 50Arms of detection. This would be important if you were building a current meter with this chip.

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Hi Paul,

Thank you for the comprehensive response.

Think that is what I was not understanding!!