MICRF114 datasheet(4/34 Pages) MICROCHIP

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MICRF114

DS50002416A-page 4

Preliminary

 2015 Microchip Technology Inc.

1.3

Pin Descriptions

Table 1-1 describes the MICRF114 pins.

1.4

Power Management

The MICRF114 has a single power pin and a single

ground pin. The sensitive analog blocks run from an

internal LDO, which does not need an external

capacitor. A bias and reference circuit provides

reference voltage to the LDO and bias currents to all

analog blocks.

The digital block runs from the unregulated supply. This

enables communication with the MCU even when most

of the blocks (including the LDO) are turned off to save

power. Additionally, the MICRF114 retains its self-

calibration result and user-programmable parameters

in this low-power state. To get the highest possible

efficiency, the RF Power Amplifier (PA) block runs

directly from the unregulated supply.

A POR circuit keeps the MICRF114 in a Reset state

until the supply voltage is sufficient for proper operation

of the digital block. The POR event resets the device

control state machine and the Configuration register to

their default state. A Reset is also triggered by

sufficiently large supply voltage glitches and brown-out.

1.5

MCU Interface

A proprietary 2-wire serial interface consisting of a

clock line and a data line is utilized to control the

operation of the MICRF114 and to input the transmit

data packet. Special start and stop conditions on these

two lines indicate the beginning and end of

communication with the MCU. Except during these

Start and Stop bits, the MCU must change the data

only when the clock is at logic low. Control and

Configuration bits are sent synchronously, and the

MICRF114 samples the data on the rising edge of the

clock. Transmit data is sent asynchronously with the

clock held low. During transmission, the serial data line

is connected directly to the RF modulator. The

assembly and timing of the data packet are the

responsibilities of the MCU.

1.6

Device Control

Data transmission start and stop are always initiated by

the MCU. Programmable transmit parameters are

stored in a single 16-bit register. The value in this

The MCU can rewrite the register at the beginning of

each transmission. Immediately after POR or at the

beginning of a transmission, an internal state machine

turns on the various blocks of the MICRF114 with the

required sequence and timing and then performs an

automatic calibration of the device when required. The

MCU must wait for these operations to be completed

before sending the transmit data packet.

An initial calibration is done after POR. The calibration

result is kept as long as the supply voltage is present.

Recalibration can be requested by the MCU when

required.

1.7

Crystal Oscillator

The reference frequency source is a single-pin crystal

oscillator. The transmit frequency is 32 times the

reference. Thus, the relative accuracy of the crystal

oscillator directly determines the accuracy of the

transmit frequency. The most popular transmit

frequencies require standard and off-the-shelf low-cost

crystals. The oscillator operates at parallel resonance.

The load capacitor that the crystal requires is

integrated to minimize the BOM. To accommodate

various crystal types and compensate for PCB parasitic

capacitances, the value of this load capacitor is

programmable by the MCU.

The other function of the crystal oscillator is to provide

a relatively accurate clock frequency for the automatic

calibration circuit. As the crystal frequency is

determined by the transmit frequency and can vary

over a wide range, the clock is generated by dividing

the crystal frequency by a programmable number that

must be properly set

to achieve the expected

performance.

TABLE 1-1:

MICRF114 PIN DESCRIPTIONS

Name

Type

Description

SCK

Digital Input

MCU interface serial clock input

SDI

Digital Input

MCU interface serial configuration or TX data input

VDD

Power

Positive supply voltage

RFO

Analog Output

RF TX output

VSS

Power

Ground reference

OSC

Analog Input

Reference crystal connection

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