Z8F2480 Datasheet, PDF (17/24 Pages) Zilog, Inc. – Load current up to 3 amps

Z8F2480 Power Monitor with an eZ80F91 Webserver
Reference Design
b. Note that the voltage on PB5 of the Z8F2480 determines whether the amplifier’s
high-gain or low-gain range is used.
2. Typically, the amplifier will be configured for low gain when the load current is above
810 mA RAM, and low gain when the load current is below 770 mA RMS. Between
770 mA and 810 mA, either gain setting can be used. Additionally, note that these
thresholds will vary from one development kit to the next, as determined by the char-
acteristics of their respective circuit components.
3. The calibration process is then performed for each step in the upper current range
recording (x,y) values, in which the x value corresponds to the average ADC reading
value, and the y value corresponds to the actual AC load current (RMS).
a. The default transfer equation used in the javascript for low-gain current is:
I = 0.96950933849967 * LoadCurrent + 15.774942218407
b. As with voltage measurements, the output of the i2c_trace on console com-
mand can be used to obtain the ADC values.
4. Use the same linear least-square regression analysis to determine the calibrated slope
and coefficient to be used in the javascript equation.
5. Repeat the low-gain calibration to obtain the desired input accuracy.
High-Gain Current Calibration
The process for calibrating the high-gain slope and intercept values in the javascript trans-
fer equation are very similar to the low-gain calibration process. The only difference is to
use load currents below the low-to-high-gain threshold of the measurement board (nomi-
nally at an ADC input voltage of 810mA).
The default high-gain transfer equation is:
I = 5.183353039 * (LoadCurrent & 0x7FFF) + 42.05404895723
Electrical Specifications
This section describes the electrical characteristics of this reference design and reflects all
available data as a result of testing prior to qualification and characterization. As such, the
data presented in this document is subject to change.
Table 1 lists the maximum voltage, current and temperature ratings for this reference design.
Table 1. Absolute Maximum Ratings
Parameter
Rating
Unit
AC voltage RMS maximum
250
V
Load current
3.3
A
Note: The maximum AC rating is 250 V; however, normal operation ranges up to 240 V
only. When input voltage exceeds 240 V, the web page shown in Figure 5 will display a
warning message.
RD002702-0814
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