WIRELESS CONNECTIVITY & SENSORS
Evaluation board user manual
Beware of IO level incompatibility. The host must obey the values stated in the module’s man-
ual. Especially the IO level restrictions must be implemented by a host system (i.e. using a
level shifter to use the allowed IO levels).
3.5.5 LFXO crystal
For higher LFCLK accuracy (better than ±250 ppm) a low frequency crystal oscillator of 32.768 kHz
(LFXO) shall be used. A crystal, 3.2 ×1.6 mm package, for example
, can be placed
on the evaluation board to position Q1. The needed load capacitance can be reached with ca-
pacitors C9 and C10, 0402 package.
nRF52840 pin P0.00/XL1 and P0.01/XL12 are connected to module pad LED_1 and LED_2
respectively. If a LFXO is mounted to the EV board the JP2.7-8 and JP2.9-10 jumpers shall
not be connected, therefore the LED_1 and LED_2 function is no longer available.
Figure 8: LFXO mounting
The input capacitance of the pad LED_1 and LED_2 are 4 pF. The values of C9 and C10 can
be calculated as follows.
The load capacitance of LFXO is given by
C
l
=
C
9
l
∗
C
10
l
C
9
l
+
C
10
l
(1)
If
C
9
l
=
C
10
l
= C, then
C
l
=
C
2
(2)
whereas,
C
9 =
C
−
C
XL
1
−
C
P CB
(3)
C
10 =
C
−
C
XL
2
−
C
P CB
(4)
C
l
= Load capacitance of LFXO crystal.
C
XL
1
= Input capacitance of Pad LED_1 (4 pF)
C
XL
2
= Input capacitance of Pad LED_2 (4 pF)
Thyone-I, Proteus-III(-SPI), Setebos-I
20
Version 1.5, May 2023