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

Z8F2480 Power Monitor with an eZ80F91 Webserver
Reference Design
A block diagram of the Power Board is shown in Figure 3.
Figure 3. Block Diagram: A Z8F2480 Power Monitor and eZ80F91
Webserver with a Range Switch
Warning: The Power Board is electrically connected to AC power. It contains points with high
voltage (up to 400 V). If any measurements will be performed on the Power Board, a
power supply with an isolation transformer should be used to avoid electrical shock.
Persons working with this Power Board should be fully qualified to work with high
voltage devices.

Load current is not fuse-protected. It is up to the user to protect the AC line in the event
of a short circuit caused by a load connected to the Power Board.
Z8F2480 Power Monitor
The Z8F2480 Power Monitor (i.e, the Power Board) contains an auxiliary power supply
with a depletion-mode MOSFET (Q1; IXTA08N50D2), a Zener diode (ZD1), and resis-
tors R1 and R2, which provide +5 V to drive a voltage regulator (U3). The 3.3 V output of
U3 in turn drives the Z8F2480 MCU and the optically-isolated I²C interface. A MOSFET
(Q2), operated by the Z8F2480 MCU, is used to decrease power dissipation on Q1 by
turning Q1 off when AC voltage is significantly above the voltage stored on capacitor
CE1. For a visual representation of this circuit, see Appendix A. Schematic Diagrams on
page 22.
Resistive dividers RS1–RS3/RS4 provide a signal to the Z8F2480 MCU for AC voltage
measurements, while resistive dividers R46–R48/R9 furnish a signal to the MCU’s inter-
nal comparator to synchronize the Q2 gate signal with the AC phase.
RD002702-0814
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