CDB5460AU Cirrus Logic Inc, CDB5460AU Datasheet - Page 13

• Manufacturer Part Number: CDB5460AU
• Description: EVALUATION BOARD FOR CS5460A
• Manufacturer: Cirrus Logic Inc

Specifications of CDB5460AU

• Main Purpose: Power Management, Energy/Power Meter
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: CS5460A
• Primary Attributes: 1-Phase Current & Voltage Monitoring
• Secondary Attributes: Graphical User Interface, SPI™ & USB Interfaces
• Processor To Be Evaluated: CS5460A, C8051F320
• Interface Type: USB
• Operating Supply Voltage: 5 V
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Figure 3) will be enabled on the other channel; in
order to preserve the relative phase relationship
between the voltage-sense and current-sense in-
put signals. For example, if the HPF is engaged for
the voltage channel, but not the current channel,
then the APF will be engaged in the current channel,
to nullify the additional phase delay introduced by
the high-pass filter in the current channel.
2.1.5 Overall Filter Response
When the CS5460A is driven with a 4.096 MHz
clock (K = 1), the composite magnitude response
(over frequency) of the voltage channel’s input fil-
ter network is shown in Figure 4, while the com-
posite
channel’s input filter network is given in Figure 5.
Note that the composite filter response of both
channels scales with MCLK frequency and K.
2.1.6 Gain and DC Offset Adjustment
After filtering, the instantaneous voltage and cur-
rent digital codes are subjected to offset/gain ad-
justments, based on the values in the DC offset
registers (additive) and the gain registers (multipli-
cative). These registers are used for calibration of
the device (see Section 3.8, Calibration). After off-
set and gain, the 24-bit instantaneous data sample
values are stored in the Instantaneous Voltage and
Current Registers.
2.1.7 Real Energy and RMS Computations
The digital instantaneous voltage and current data
is then processed further. Referring to Figure 3, the
DS487F4
CURRENT
VOLTAGE
magnitude
∆Σ
∆Σ
DELAY
REG
SINC 2
SINC 4
Configuration Register *
response
PC[6:0] Bits
DELAY
REG
FIR
FIR
of
the
HPF
APF
HPF
APF
Figure 3. Data Flow.
current
V
I
DCoff
DCoff
+
+
*
*
instantaneous voltage/current data samples are
multiplied together (one multiplication for each pair
of voltage/current samples) to form instantaneous
(real) power samples. After each A/D conversion
cycle, the new instantaneous power sample is
stored in the Instantaneous Power Register.
The instantaneous power samples are then
grouped into sets of N samples (where N = value in
Cycle Count Register). The cumulative sum of
each successive set of N instantaneous power is
used to compute the result stored in the Energy
Register, which will be proportional to the amount
of real energy registered by the device during the
most recent N A/D conversion cycles. Note from
Figure 3 that the bits in this running energy sum
are right-shifted 12 times (divided by 4096) to
avoid overflow in the Energy Register. RMS calcu-
lations are also performed on the data using the
last N instantaneous voltage/current samples, and
these results can be read from the RMS Voltage
Register and the RMS Current Register.
2.2 Performing Measurements
To summarize Section 2.1, the CS5460A performs
measurements of instantaneous current and in-
stantaneous voltage, and from this, performs com-
putations of the corresponding instantaneous
power, as well as periodic calculations of real en-
ergy, RMS current, and RMS voltage. These mea-
surement/calculation results are available in the
form of 24-bit signed and unsigned words. The
scaling of all output words is normalized to unity
V
I
gn
gn
x
x
*
*
x
P
V *
* DENOTES REGISTER NAME
+
I *
off
*
x
x
V
I
ACoff
ACoff
P *
-
-
*
*
SINC 2
SINC 2
N
Σ
TBC *
E to F
x
N
N
÷ 4096
PULSE-RATE*
CS5460A
÷
E *
E
E
÷
N
out
dir
N
V
I
RMS
RMS
*
*
13