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PCF7900 Schematic ( PDF Datasheet ) - NXP Semiconductors

Teilenummer PCF7900
Beschreibung Fractional-N Transmitter IC
Hersteller NXP Semiconductors
Logo NXP Semiconductors Logo 




Gesamt 30 Seiten
PCF7900 Datasheet, Funktion
PCF7900
PCH7900
Fractional-N Transmitter IC (FraNTIC)
Product Specification
Confidential
2007 Dec 13






PCF7900 Datasheet, Funktion
NXP Semiconductors
Fractional-N Transmitter IC (FraNTIC)
Product Specification
PCF7900 / PCH7900
Figure 2. Package Outline TSSOP16
2007 Dec 13
6
Confidential

6 Page









PCF7900 pdf, datenblatt
NXP Semiconductors
Fractional-N Transmitter IC (FraNTIC)
5.3 Transmitter operating modes
Power down mode
If the EN pin is kept low for at least 216 XTAL clocks (~5ms
at 13.08MHz crystal frequency), the transmitter (PLL,
power amplifier and crystal oscillator) will be reset, the bit-
counter inside the SPI counting the already transferred bits
is set to zero, SCK and SDIO are disabled (also SDO, if
used) and the device will enter the power down mode. In
this state the TXCON bit PLLEN is cleared. The total
current consumption is almost zero.
Another possibility to enter the power down mode is to set
the PD bit in the TXCON register.
When the Power down mode is left (by rising edge of EN)
the PD bit is cleared.
XTAL Active mode
With rising edge of EN the Power down mode is left and
the crystal oscillator is activated. The XTAL clock will be
stable after tXTAL,SET. The SPI is activated, so the SFR’s can
be programmed. The XTAL Active mode can be left by
either activating the PLL (set PLLEN in TXCON) or by
entering the Power down mode.
PLL Active mode
If the XTAL Active mode is active and the crystal oscillator
is settled, the PLL can be switched on (after tXTAL,SET).
Setting the bit PLLEN in the register TXCON directly
powers on the PLL. The VCO output frequency will be
stable after tACQ. This mode stays active as long as EN is
kept 1 or as long EN is kept 0 for a period shorter than 216
XTAL clock cycles. If EN is kept 0 for a longer period or the
PD bit in TXCON is set, the device returns to Power down
mode. By resetting the PLLEN bit in TXCON the PLL is
turned off and XTAL Active mode is entered again. Another
possibility to leave the PLL active mode is to send a
dedicated SPI command (antenna tune or transmit
command).
Antenna Tune mode
To enter the Antenna Tune mode a dedicated SPI
command, the antenna tune command, has to be sent
when the device is in PLL Active mode. It is also possible
to send the antenna tune command when in Transmitter
Active mode. The Antenna Tune mode will then be kept
while EN remains high. During the antenna tune command
the SPI output (either SDIO or SDO, depending on the
configuration of the SPI interface – see Table 2) has to be
checked for a negative edge indicating the tuned state. By
setting EN to 0 the antenna tune command is finished and
the PLL active mode (or Transmitter Active mode –
depending on the configuration settings) is entered again.
Product Specification
PCF7900 / PCH7900
Transmitter Active mode
The Transmitter Active mode can only be entered upon a
SPI command. This only is possible if the PLLEN bit is set
(with a previous SPI command). Dependent of the
configuration coded into the transmit command, the
Transmitter Active mode can be left when either EN set low
directly, or when EN is set low in a synchronized way with
the edge of the last data-bit (in both cases the PLL Active
mode is entered) or upon direct SPI register setting (then
XTAL Active mode is entered). If a POR or power fail
condition occurs during a transmit sequence, the XTAL
Active mode is entered.
By setting the PD bit in TXCON the transmitter is turned off
and the device enters the Power down mode. This also
happens if EN is kept 0 for a period longer than 216 XTAL
clocks.
When the device is in the Transmitter Active mode SPI
communication (change of register contents) is possible
(depending on the configuration settings), if it is done within
one bit (or during a constant bit stream).
For this feature EN has to be set low right after the
beginning of one transmitted bit and set high again. Then
SPI communication is enabled for commands. Afterwards
transmitting new data can be activated again with another
dedicated transmit command. During the SPI
communication the transmitted data will keep unchanged. It
is also allowed to send an antenna tune command when
the device is in Transmitter Active mode.
With the first transmitted string the power amplifier is
activated and (only here!) the baud rate generator is reset.
When the transmit-phase is interrupted with an SPI
communication and the transmit-phase is re-started, the
baud rate generator will keep synchronized with the
previous string. No jitter will occur, when switching from the
previous to the next string.
After the transmission of data-bits the PLLEN bit can be
read. The brown out detection monitors the actual
regulated supply voltage and indicates proper supply-
condition during the whole transmission phase. If PLLEN is
cleared the supply voltage has dropped below the minimum
required voltage level and the transmission will be
interrupted. To restart a transmission a new transmit
command has be sent after the PLL is enabled again.
2007 Dec 13 12 Confidential

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