NRF902 Datasheet, PDF (9/13 Pages) List of Unclassifed Manufacturers – Single chip 868 MHz Transmitter

PRELIMINARY PRODUCT SPECIFICATION
nRF902 Single chip 868 MHz Transmitter
Clock mode
Clock mode is available so that an external microprocessor may have a reference
signal without the cost of a second crystal. In Clock mode, the crystal oscillator and
reference clock outputs are operating, while the rest of the transmitter is disabled. The
reference signal from the internal crystal oscillator is divided by 8 by use of a
prescaler, this signal is available at the XO8 pin.
Clock mode may be set by connecting the power adjusting resistor R2 to ground or by
leaving it open (see Figure 10). Current consumption in Clock mode is typically 200
µA when no load is applied at the XO8 clock output pin. If a capacitive load is
applied at the XO8 output, then current consumption in Clock mode will increase.
Start-up time when switching between Clock mode and Transmit mode is extremely
fast, typically 30µs.
X1 13.567MHz
VDD
Clock
Output
VDD
R1
xtal ¹
R2
2
REXT
3
XO8
VDD ⁴
C1
C2
nRF902
8
VSS
7 _ant1
6 _ant2
5
FSK
Matching Network/
Antenna
Data
Input
Figure 10. FSK transmitter in Clock mode
XO8 Clock Output Pin Capacitance
The frequency of the clock signal is 1/8th of the crystal frequency i.e. a crystal
frequency of 13.567 MHz will result in an output clock frequency of 1.695 MHz. The
XO8 output signal will be present in Transmit mode and Clock mode. In Power Down
mode the XO8 signal will be a logic “0”.
The capacitive load at the XO8 pin will affect current consumption in Clock mode. If
the pin is left open the current consumption will typically be 200uA. Adding a
capacitive load, such as microcontroller load [C_ML] to the XO8 pin will result in an
increase in the current consumption, the increase ∆I is given as:
∆I = f_XO8 ⋅VDD⋅ C_ML
Example
With a capacitive load of C_ML = 5pF, using VDD=3.0 V and a 13.567 MHz crystal,
the current increase ∆I becomes :
∆I = f_XO8 ⋅VDD⋅ C_ML = ((13 .567 MHz) / 8) ⋅ 3.0 V ⋅ 5 pF = 25 uA.
The typical current consumption will increase to 225uA when adding C_ML=5 pF.
Nordic VLSI ASA
Revision: 1.0
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Page 9 of 13
April 2000