Data Sheet

BMD-345 - Data sheet
UBX-19039908 - R07 Electrical specifications Page 15 of 36
The BMD-345 also supports ETM and ITM trace. The trace data from the ETM and the ITM is sent to
an external debugger via a 4-bit wide parallel trace port. In addition to parallel trace, the TPIU supports
serial trace via the Serial Wire Output (SWO) trace protocol.
3.7 Clocks
The BMD-345 requires two clocks, a high frequency clock and a low frequency clock. The high
frequency clock is provided on-module by a high-accuracy 32 MHz crystal as required by the
nRF52840 for radio operation.
The low frequency clock can be provided internally by an RC oscillator or synthesized from the fast
clock, or externally by a 32.768 kHz crystal. An external crystal provides the lowest power
consumption and greatest accuracy. Using the internal RC oscillator with calibration provides
acceptable performance for Bluetooth low energy applications at a reduced cost and slight increase
in power consumption.
3.7.1 32.768 kHz crystal (LFXO)
Symbol
Parameter
Typ.
Max.
Unit
F
NOM_LFXO
Crystal frequency
32.768
-
kHz
F
TOL_LFXO_BLE
Frequency tolerance, Bluetooth low energy
applications
1
-
±500
ppm
f
TOL_LFXO_ANT
Frequency Tolerance, ANT applications
2
-
±50
ppm
C
L_LFXO
Load Capacitance
-
12.5
pF
C
0_LFXO
Shunt Capacitance
-
2
pF
R
S_LFXO
Equivalent series resistance
-
100
kΩ
C
pin
Input Capacitance on XL1 & XL2 pads
4
-
pF
Table 10: 32.768 kHz crystal (LFXO)
3.7.2 32.768 kHz clock source comparison
Symbol
Parameter
Min.
Typ.
Max.
Unit
I
LFXO
Current for 32.768 kHz Crystal Oscillator
-
0.23
-
µA
I
LFRC
Current for 32.768 kHz RC Oscillator
-
0.7
1
µA
I
LFSYNT
Current for 32.768 kHz Synthesized Oscillator
-
100
-
µA
f
TOL_LFXO_BLE
Frequency Tolerance, 32.768 kHz Crystal Oscillator (Bluetooth low
energy Stack)
3
-
-
±500
ppm
f
TOL_LFXO_ANT
Frequency Tolerance, 32.768 kHz Crystal Oscillator (ANT Stack)
4
-
-
±50
ppm
f
TOL_LFRC
Frequency Tolerance, 32.768 kHz RC Oscillator
-
-
±5
%
f
TOL_CAL_LFRC
Frequency tolerance, 32.768 kHz RC after calibration
-
-
±500
ppm
f
TOL_LFSYNT
Frequency Tolerance, 32.768 kHz Synthesized Oscillator
-
-
±48
ppm
Table 11: 32.768 kHz clock source comparison
1
f
TOL_LFXO_BLE
and f
TOL_LFXO_ANT
are the maximum allowed for Bluetooth low energy and ANT applications. Actual tolerance
depends on the crystal used.
2
The ANT protocol requires the use of an external crystal.