Cirrus Logic CS5462 - Manual (Page 11)

CS5462
DS547F1 11
4.2.2 Mechanical Counter Format
In mechanical counter mode, the CS5462 produc-
es pulses on E1 and E2 which can be used to drive
a bi-directional mechanical counter. Each pin pro-
duces active-low pulses which have pulse widths
of 125 ms or 15 ms, depending on the frequency
selected. In the figure below, the frequency and
corresponding pulse width is shown for each op-
tion available. In this mode when energy is posi-
tive, the pulses appear on E1; when energy is
negative, pulses appear on E2.
4.3 Energy Direction Indicator
For either pulse output mode, the NEG pin can be
used to indicate the direction of the energy calcu-
lated. The NEG pin is updated at the sample rate
of the converter. If negative energy is detected the
NEG pin will become active low and will remain ac-
tive low until positive energy is detected.
4.4 Internal Calibration Option
For most power meter applications the standard
accuracy requirements require the meter be cali-
brated to within a certain percentage. Calibrating a
CS5462 meter can be done a number of ways.
One calibration method is to externally adjust the
front-end input circuit by using a potentiometer or
resistor network. By adjusting the amount of gain in
the resistor divider on the front end the energy out-
puts can be adjusted to fit the accuracy required.
Although this method is available, it may be costly
to add the additional components and the accuracy
required is often difficult to achieve. As an alterna-
tive the CS5462 is designed to allow the user to
calibrate the part without the need for external po-
tentiometers or resistor networks. The CS5462
provides a digital on-chip calibration solution. This
digital alternative can calibrate energy registration
error to within 0.1% without any analog adjust-
ments.
This calibration is accomplished by connecting
each Configuration Input pin, CAL1 and CAL0, to
one of the Program Select Output pins, P1 - P7. At
startup the CS5462 will scan the CAL1 and CAL0
pins to discern what connections are made, and
then calibrate the gain accordingly.
CAL1 and CAL0 each have seven options which
allows for 49 different steps of 0.2% between
+4.8% and -4.8% of expected energy output. Be-
fore startup, CAL1 and CAL0 must each be con-
nected to only one of the program select pins.
To Calibrate the CS5462:
1. Connect CAL1 and CAL0 to P4. This connection
will adjust the energy outputs by 0%.
2. Apply known current and voltage signals to the
inputs of the CS5462.
3. Measure the average pulse output frequency of
FOUT, E1, or E2.
4. The average frequency will be within some per-
centage of the expected frequency. Depending on
the output of the uncalibrated chip, the CAL0 and
CAL1 pins can be adjusted using the above options
(see “User Defined Settings” on page 12 for more
on calibration)
.
4.5 Power-on Reset
The CS5462 is equipped with internal circuitry that
will put the chip into reset if power supply is lost.
This is particularly useful in black-out or brown-out
situations in which the power supply temporarily in-
terrupted. The CS5462 will enter into reset if the
power drops below 2.5 V. The chip will remain in
reset until the supply rises to 4 V (See Figure 6) at
pulse width
E1
pulse width
Positive Energy Negative Energy
E2
2 Hz 16 Hz
125 ms 15 ms Pulse Width
Frequency
P6 P7
FREQ
connected to:
C A L 1
+ 4 .2 % P 1
P 2
P 4
P 6
P 7
+ 2 .8 %
0 %
-2 .8 %
-4 .2 %
C A L 0
+ 0 .6 %
+ 0 .4 %
0 %
-0 .4 %
-0 .6 %
P 3
P 5
+ 1 .4 %
-1 .4 %
+ 0 .2 %
-0 .2 %
Figure 6. Calibration Options