Datasheet

C
1
1
2 fp R´ ´ ´
IN,PGA2
C =
2
Rx C1 Rx C2
330 W
To ADC Input on MCU
From Line-Coupling Circuit
or Passive Bandpass Filter
LPF
PGA
PGA
See Note 2
Inside the AFE030
Rx_PGA1_OUT
Rx_F_IN
Rx_PGA1_
IN
Rx_PGA2_
OUT
Rx_F_
OUT
PA_IN
C
2
1
2 fp R´ ´ ´
IN,PGA1
C =
1
See Note 1
Rx_C1 Rx_C2
See Note 3
CC
1
C
2
R
1
R
2
1
2 fp R´ ´ ´
IN,PGA1
C =
L1
L2
From Line-Coupling
Circuit
To Rx PGA1
See Note 1
AFE030
www.ti.com SBOS588A –DECEMBER 2011– REVISED DECEMBER 2011
The Rx Filter is a very low noise, unity-gain, fourth-order low-pass filter. The Rx Filter cutoff frequency is
selectable between CENELEC A or CENELEC B, C, and D modes. The Control1 Register bit location 3 setting
(CA CBCD) determines the cutoff frequency. Setting Control1 Register bit location 3 to '0' selects the CENELEC
A band; setting Control1 Register bit location 3 to '1' selects the CENELEC B, C, and D bands. Because the Rx
Filter is a very low noise analog filter, two external capacitors are required to properly configure the Rx Filter.
Table 3 shows the proper capacitance values for CENELEC A, B, C, and D bands. Capacitor Rx C1 is connected
between pin 24 and ground, and Rx C2 is connected between pin 23 and ground. For the capacitors shown, it is
recommended that these components be rated to withstand the full AV
DD
power-supply voltage
Table 3. Recommended External Capacitors Required for Rx Filter
FREQUENCY BAND Rx C1, PIN 24 Rx C2, PIN 23 CUTOFF FREQUENCY (kHz)
CENELEC A 680 pF 680 pF 90
CENELEC B, C, D 270 pF 560 pF 145
Figure 32 illustrates the recommended connections for the Rx signal chain.
(1) For capacitor value C
1
, f is the desired lower cutoff frequency and R
IN,PGA1
is the input resistance of Rx PGA1.
(2) For capacitor value C
2
, f is the desired lower cutoff frequency and R
IN,PGA2
is the input resistance of Rx PGA2.
(3) Refer to Table 3.
Figure 32. Recommended Connections for Rx Signal Chain
As Figure 33 shows, a fourth-order passive passband filter is optional but recommended for applications where
high performance is required. The external passive passband filter removes any unwanted, out-of-band signals
from the signal path, and prevents them from reaching the active internal filters within the AFE030.
(1) For capacitor value C, f is the desired lower cutoff frequency and R
IN,PGA1
is the input resistance of Rx PGA1. Refer to Table 3.
Figure 33. Passive Bandpass Rx Filter
Copyright © 2011, Texas Instruments Incorporated 27
Product Folder Link(s): AFE030