COMBOSOLAR datasheet(25/57 Pages) TI1

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LPF

PGA

f 22 k

· · ·

C =

Note (3)

Tx_F_OUT

Tx_PGA_

PA_OUT1

PA_OUT2

Tx_PGA_

OUT

PA_IN

Inside the AFE031

510 W

Note (2)

MCU

Tx_F_IN1

Tx_F_IN2

GPIO

Note (1)

43 kW

AFE031

www.ti.com

SBOS531D – AUGUST 2010 – REVISED MAY 2012

(1)

When using both Tx Filter inputs, use 43-k

Ω resistors to match the input resistance for best frequency response.

(2)

Refer to Table 2.

(3)

For capacitor value C, f is the desired lower cutoff frequency and 22 k

Ω is the PA input resistance.

Figure 31. Recommended Tx Signal Chain Connections in PWM Mode

Using Two PWM Signals and Additional RC Filters

For the capacitors listed in Table 2, it is recommended that these components be rated to withstand the full AVDD

power-supply voltage.

Table 2. Recommended External R and C Values to

Increase Tx Filter Response Order in PWM

Applications

FREQUENCY BAND

R (

Ω)

C (nF)

SFSK: 63 kHz, 74 kHz

510

2.7

CENELEC A

510

1.5

CENELEC B, C, D

510

The Tx PGA and Tx Filter each have the inputs and outputs externally available in order to provide maximum

system design flexibility. Care should be taken when laying out the PCB traces from the inputs or outputs to

avoid excessive capacitive loading. Keeping the PCB capacitance from the inputs to ground, or from the outputs

to ground, less than 100 pF is recommended.

Rx Block

The Rx block consists of Rx PGA1, the Rx Filter, and Rx PGA2. Both Rx PGA1 and Rx PGA2 are high-

performance programmable gain amplifiers. Rx PGA1 can be configured through the SPI to operate as either an

attenuator or in gain. The gain steps of the Rx PGA1 are 0.25 V/V, 0.5 V/V, 1 V/V, and 2 V/V. The gain steps of

the Rx PGA2 are 1 V/V, 4 V/V, 16 V/V, and 64 V/V. Configuring the Rx PGA1 as an attenuator (at gains less

than 1 V/V) is useful for applications where the presence of large interference signals are present within the

signal band. Attenuating the large interference allows these signals to pass through the analog Rx signal chain

without causing an overload; the interference signal can then be processed and removed within the

microprocessor as necessary.

Product Folder Link(s): AFE031

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