Cirrus Logic AN337 - Manual (Page 2)

2 AN337REV1
AN337
For example, assume a 10(60)A Class 0.5 watt-hour meter using a 200 u Ω shunt as the current sensor. The
voltage on the CS5463 I-channel input (IIN±) with the starting current (I
st
= 0.1% I
b
) will be 2 uV which is
well below the I-channel noise level. Therefore, if I
RMS
was used to decide the no-load condition, the meter
will not pass the no-load and starting tests. Even though the meter has lower than 2 uV noise level and pass-
es the no-load test, this application can not be used as a 5(60)A meter because the noise level is fixed within
the application, however the starting current would be 50% lower.
In the next example, P
Active
is used as the variable.
Assume the following:
• A 5(60)A Class 0.5 watt-hour meter, AC gain calibrated, with inputs of U
n
and I
max
• P
Active
_Imax = 0.36 (decimal register value, same below) with inputs of U
n
and I
max
• P
Active
_Ib = 0.03 with inputs of U
n
and I
b
• P
Active
_Starting = 0.00003 with inputs of U
n
and starting current (Ist = 0.1% I
b
)
Typically, the residual value in the P
Active
register P
Active
_Residual is less than 0.000002 (with 150 mVrms
on VIN± and no signal on IIN±, HPFs enabled, N = 4000).
Because P
Active
_Starting >> P
Active
_Residual, the threshold can easily be selected between
P
Active
_Residual and P
Active
_Starting (a threshold of 0.00001, for example) to allow the meter pass the no-
load and starting tests.
Furthermore, if the meter is well designed and has very low system noise, the threshold can be set even
lower (e.g. 0.000005) to allow much smaller starting current which is more welcomed by electric utilities.
The meter current dynamic range (I
max
/ I
b
) can also be extended.
Contacting Cirrus Logic Support
For all product questions and inquiries contact a Cirrus Logic Sales Representative.
To find one nearest you go to
http://www.cirrus.com
IMPORTANT NOTICE
Cirrus Logic, Inc. and its subsidiaries ("Cirrus") believe that the information contained in this document is accurate and reliable. However, the information is subject
to change without notice and is provided "AS IS" without warranty of any kind (express or implied). Customers are advised to obtain the latest version of relevant
information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale
supplied at the time of order acknowledgment, including those pertaining to warranty, indemnification, and limitation of liability. No responsibility is assumed by Cirrus
for the use of this information, including use of this information as the basis for manufacture or sale of any items, or for infringement of patents or other rights of third
parties. This document is the property of Cirrus and by furnishing this information, Cirrus grants no license, express or implied under any patents, mask work rights,
copyrights, trademarks, trade secrets or other intellectual property rights. Cirrus owns the copyrights associated with the information contained herein and gives con-
sent for copies to be made of the information only for use within your organization with respect to Cirrus integrated circuits or other products of Cirrus. This consent
does not extend to other copying such as copying for general distribution, advertising or promotional purposes, or for creating any work for resale.
CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH, PERSONAL INJURY, OR SEVERE PROP-
ERTY OR ENVIRONMENTAL DAMAGE ("CRITICAL APPLICATIONS"). CIRRUS PRODUCTS ARE NOT DESIGNED, AUTHORIZED OR WARRANTED FOR USE
IN PRODUCTS SURGICALLY IMPLANTED INTO THE BODY, AUTOMOTIVE SAFETY OR SECURITY DEVICES, LIFE SUPPORT PRODUCTS OR OTHER CRIT-
ICAL APPLICATIONS. INCLUSION OF CIRRUS PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER'S RISK AND
CIRRUS DISCLAIMS AND MAKES NO WARRANTY, EXPRESS, STATUTORY OR IMPLIED, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS FOR PARTICULAR PURPOSE, WITH REGARD TO ANY CIRRUS PRODUCT THAT IS USED IN SUCH A MANNER. IF THE CUSTOMER OR
CUSTOMER'S CUSTOMER USES OR PERMITS THE USE OF CIRRUS PRODUCTS IN CRITICAL APPLICATIONS, CUSTOMER AGREES, BY SUCH USE, TO
FULLY INDEMNIFY CIRRUS, ITS OFFICERS, DIRECTORS, EMPLOYEES, DISTRIBUTORS AND OTHER AGENTS FROM ANY AND ALL LIABILITY, INCLUD-
ING ATTORNEYS' FEES AND COSTS, THAT MAY RESULT FROM OR ARISE IN CONNECTION WITH THESE USES.
Cirrus Logic, Cirrus, and the Cirrus Logic logo designs are trademarks of Cirrus Logic, Inc. All other brand and product names in this
document may be trademarks or service marks of their respective owners.