maxq3180-ran Maxim Integrated Products, Inc., maxq3180-ran Datasheet - Page 36

• Manufacturer Part Number: maxq3180-ran
• Description: Low-power, Multifunction, Polyphase Afe
• Manufacturer: Maxim Integrated Products, Inc.

A simple first-order highpass filter (HPF) is used.The fil-
ter formula is:
The filter coefficient (hpf_b0f) is a signed 16-bit value
and can be configured by the master.
The digital integrator block can be engaged separately
for each current phase (IA, IB, IC) and for neutral cur-
rent (IN) by setting configuration bits INTGA, INTGB,
INTGC, and INTGN in the CONNCT register. When
enabled, the digital integrator block calculates the inte-
gral of the input current signal (i.e., sum of samples)
and then feeds this integral into the processing path
instead of the current sample. This sum can produce a
DC offset that must be removed by an additional HPF
stage. The HPF can be combined with the integrator in
a single formula:
where hpf_b0f is the same coefficient used in the
stand-alone HPF stage. The integrator increases the
amplitude of accumulation by approximately (NS/2π),
where NS is the number of samples per line cycle (fac-
tor approximately 16 for 50Hz signal and 200µs sam-
pling rate). The output of the integrator is scaled down
by factor 16 in the MAXQ3180.
The HPF, when combined with the digital integrator,
introduces an additional phase shift into the current
Low-Power, Multifunction, Polyphase AFE
Figure 8. DSP Flow
36
______________________________________________________________________________________
Y
n
= (1 - hpf_b0f/2
Y
n
= (1 - hpf_b0f/2
I
V
HPF
HPF
16
PHASE ANGLE COMPENSATION
) x (Y
16
) x (Y
Highpass Filter (HPF)
n-1
INTEGRATOR
n-1
+ X
+ HPF
HPF
BPF
BSF
+ X
n
- X
n
)
n-1
Integrator
)
SV
SI
S
2
2
channel. To compensate for this, the second HPF stage
is automatically engaged in the voltage processing
path when the current integrator is active.
The power calculation engine can work in one of three
modes: full, fundamental, and harmonics. The mode of
operation is selected by the HRM configuration bits.
• HRM = 00b—Full mode. Neither the bandpass or the
• HRM = 01b—Fundamental mode. The voltage chan-
• HRM = 10b—Harmonics mode. The voltage channel
Both filters, the BPF and BSF, are second-order filters and
use the same set of coefficients. The filter formulas are:
BPF:
BSF:
Y
Y
n
bandstop filters are applied.
nel signal is put through the bandpass filter (BPF).
This BPF is centered on the fundamental frequency,
so only fundamental power is measured.
signal is put through the bandstop filter (BSF). That
BSF is centered on the fundamental frequency, so
fundamental power is removed and only harmonics
power is measured.
n
= 2Y
(2Y
= 2Y
n-2
n-1
n-1
- X
- Y
- Y
REACTIVE
n
V
I
ACTIVE
n-2
2
2
n-2
_RMS
- X
_RMS
Fundamental and Harmonics Modes
LINEARITY CALIBRATION
+ (bpf_b0f/2
(bpf_a1f/2
n-2
+ X
GAIN, OFFSET, AND
) + (bpf_a1f/2
n
- 2X
n-1
20
20
) x Y
- X
) x (2Y
n-2
20
n-1
) x (X
+ (bpf_b0f/2
n-2
P.I2
P.A
P.R
P.V2
n-1
+ X
- Y
n
- X
n-1
20
n-2
)
) x
) -