SI4464 datasheet(45/56 Pages) SILABS

45 / 56 page

Si4464/63/61/60

Rev 1.2

Selecting shorter conversion times will result in lower ADC resolution and longer times will result in higher ADC

resolution.



GPIO_ATT[3:0] - Sets attenuation of gpio input voltage when vgpio measured. Defaults to 0xC if ADC_CFG is 0.

0x0 = ADC range 0 to 0.8V. GPIO_ADC_DIV = 2560

0x4 = ADC range 0 to 1.6V. GPIO_ADC_DIV = 1280

0x8 = ADC range 0 to 2.4V. GPIO_ADC_DIV = 853.33

0x9 = ADC range 0 to 3.6V. GPIO_ADC_DIV = 426.66

0xC = ADC range 0 to 3.2V. GPIO_ADC_DIV = 640

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Response

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GPIO_ADC[15:0] - ADC value of voltage on GPIO

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BATTERY_ADC[15:0] - ADC value of battery voltage

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TEMP_ADC[15:0] - ADC value of temperature sensor voltage

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RESERVED[7:0] - RESERVED FOR FUTURE USE

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RESERVED[7:0] - RESERVED FOR FUTURE USE

8.4. Low Battery Detector

The low battery detector (LBD) is enabled and utilized as part of the wake-up-timer (WUT). The LBD function is not

available unless the WUT is enabled, but the host MCU can manually check the battery voltage anytime with the

auxiliary ADC. The LBD function is enabled in the GLOBAL_WUT_CONFIG API property. The battery voltage will

be compared against the threshold each time the WUT expires. The threshold for the LBD function is set in

GLOBAL_LOW_BATT_THRESH. The threshold steps are in increments of 50 mV, ranging from a minimum of

1.5 V up to 3.05 V. The accuracy of the LBD is ±3%. The LBD notification can be configured as an interrupt on the

nIRQ pin or enabled as a direct function on one of the GPIOs.

8.5. Antenna Diversity

To mitigate the problem of frequency-selective fading due to multipath propagation, some transceiver systems use

a scheme known as antenna diversity. In this scheme, two antennas are used. Each time the transceiver enters RX

mode the receive signal strength from each antenna is evaluated. This evaluation process takes place during the

preamble portion of the packet. The antenna with the strongest received signal is then used for the remainder of

that RX packet. The same antenna will also be used for the next corresponding TX packet. This chip fully supports

antenna diversity with an integrated antenna diversity control algorithm. The required signals needed to control an

external SPDT RF switch (such as a PIN diode or GaAs switch) are available on the GPIOx pins. The operation of

these GPIO signals is programmable to allow for different antenna diversity architectures and configurations. The

antdiv[2:0] bits are found in the MODEM_ANT_DIV_CONTROL API property descriptions and enable the antenna

diversity mode. The GPIO pins are capable of sourcing up to 5 mA of current; so, it may be used directly to

forward-bias a PIN diode if desired. The antenna diversity algorithm will automatically toggle back and forth

between the antennas until the packet starts to arrive. The recommended preamble length for optimal antenna

selection is 8 bytes.

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