SA9605A
OUTPUT SIGNALS
Pulse and Direction Output (FOUT1, DIR)
Waveforms displaying the FOUT1 and DIR signal information
for each of the three phases are shown in Figure 5.
Pulse Output (FOUT2)
Although FOUT1 has a fixed frequency output, the table
below shows the various frequencies selectable for different
rated conditions on FOUT2.
8.9µs
71µs
Table 1: User selectable FOUT2 frequency
PGM1
VSS
PGM0
VSS
Divider FOUT2 Frequency (Hz)
DIR
Phase 1
Positive
FOUT1
227
303
454
5.110
3.833
2.555
DIR
Phase 1
Negative
VSS
VDD
FOUT1
VDD
VSS
DIR
Phase 2
Positive
The frequencies shown in the above table were chosen to
allow a 4 - 3 - 2 scaling ratio for rated conditions. This facility
provides ease of interface with applications which use the
same post divider with mechanical counter or unchanged
microcontroller software for different current rated kWh
meters.
FOUT1
DIR
Phase 2
Negative
FOUT1
DIR
Phase 3
Positive
FOUT1
DIR
Phase 3
Negative
For example, a meter manufacturer may wish to build meters
for 3 system configurations with rated current loading of 80A,
60A and 40A.
FOUT1
Figure 5: FOUT1 and DIR waveforms
These waveforms demonstrate how to establish the direction
of energy flow as well as the phase from which the energy is
measured. The direction of energy is indicated on the DIR
pin, it is high for positive energy flow and low for negative
energy flow. The state of DIR is valid for the entire low period
of the FOUT1 pulse. The phase to which the pulse on the
FOUT1 pin refers to, can be ascertained by counting the
number of falling edges on the DIR pin prior to the falling edge
of the FOUT1 pulse.
The only changes which have to be implemented to interface
the device to different rated systems are to change the
current sense resistors and select the required PGM0 and
PGM1. No change to the post divider or microcontroller
software is required if the FOUT2 pin is used.
OSCILLATOR
The SA9605A contains a crystal oscillator driver circuit
requiring only an external crystal to be connected between
OSC1 and OSC2. All other components are integrated on the
device. The recommended crystal is a TV colour burst crystal
(3.5795MHz).
The output on FOUT1 is a pulse density signal representing
the instantaneous power/energy measurement. The pulse
width (tp) is 71μs. The output frequency may be calculated
using the following formula:
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퐼ꢁꢂ × 퐼푉ꢂ + 퐼ꢁꢃ × 퐼푉ꢃ + 퐼ꢁ3 × 퐼푉3
푓
퐶ꢅ푌푆푇ꢆ퐿
푓 = 12946 ×
×
ꢃ
ꢄ.5795
ꢄ × 퐼ꢅ
where
IIX is the input current on the current sense inputs on the
respective channel in RMS (16μA at rated conditions),
IVX is the input current on the voltage sense input on the
respective channel in RMS (14μA at rated conditions),
IR is the reference current on VREF, typically 50μA, and
fCRYSTAL is the frequency of the crystal used in MHz.
SPEC-3118 (REV. 3)
29-09-2017
6/11
SAMES [ SAMES ]
