User's Manual

BL652
Datasheet
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BL652 On-chip 32.768 kHz RC Oscillator
(±250 ppm) LFRC
Optional External Higher Accuracy (±20 ppm)
32.768 kHz Crystal-based Oscillator XO
Calibration
Calibration required regularly (default eight
seconds interval)
Calibration takes 16-17 ms; with DCDC used,
the total charge of a calibration event is 7.4 uC.
The average current consumed by the
calibration depends on the calibration interval
and can be calculated using the following
formula:
CAL_charge/CAL_interval
The lowest calibration interval (0.25 seconds)
provides an average current of (DCDC
enabled):
7.4uC / 0.25s = 29.6uA
To get the 250 ppm accuracy, the BLE stack
specification states that a calibration interval
of eight seconds is enough. This gives an
average current of:
7.4uC / 8s = 0.93 uA
Added to the LFRC run current and Standby
Doze (IDLE) base current shown above results
in a total average current of:
LFRC + CAL = 1.8 + 0.93 = 2.7uA
Not applicable
Total
2.7 uA
1.45 uA
Summary
 Low current consumption
 Accuracy 250 ppm
 Lowest current consumption
 Needs external crystal
 High accuracy (depends on the crystal, usually
20 ppm)
Table 27: Optional external 32.768 kHz crystal specification
Optional external 32.768kHz crystal
Min
Typ
Max
Crystal Frequency
-
32.768 kHz
-
Frequency tolerance requirement of BLE stack
-
-
±250 ppm
Load Capacitance
-
-
12.5 pF
Shunt Capacitance
-
-
2 pF
Equivalent series resistance
-
-
100 kOhm