JN5148/001,531 NXP Semiconductors, JN5148/001,531 Datasheet - Page 20

• Manufacturer Part Number: JN5148/001,531
• Description: Microcontrollers (MCU) 32bit RISC 2.4GHz
• Manufacturer: NXP Semiconductors

Specifications of JN5148/001,531

• Core: RISC
• Operating Supply Voltage: 2 V to 3.6 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN-56
• Minimum Operating Temperature: - 40 C
• Lead Free Status / Rohs Status: Details

5.2 32kHz System Clock
The 32kHz system clock is used for timing the length of a sleep period (see section 21 Power Management and
Sleep Modes) and also to generate the system clock used internally during reset. The clock can be selected from
one of three sources through the application software:
Upon a chip reset or power-up the JN5148 defaults to using the internal 32kHz RC Oscillator. If another clock source
is selected then it will remain in use for all 32kHz timing until a chip reset is performed.
5.2.1 32kHz RC Oscillator
The internal 32kHz RC oscillator requires no external components. The internal timing components of the oscillator
have a wide tolerance due to manufacturing process variation and so the oscillator runs nominally at 32kHz ±30%. To
make this useful as a timing source for accurate wakeup from sleep, a frequency calibration factor derived from the
more accurate 16MHz clock may be applied. The calibration factor is derived through software, details can be found
in section 11.3.1. For detailed electrical specifications, see section 22.3.11.
5.2.2 32kHz Crystal Oscillator
In order to obtain more accurate sleep periods, the JN5148 contains the necessary on-chip components to build a
32kHz oscillator with the addition of an external 32.768kHz crystal and two tuning capacitors. The crystal should be
connected between 32KXTALIN and 32KXTALOUT (DIO9 and DIO10), with two equal capacitors to ground, one on
each pin. Due to the small size of the capacitors, it is important to keep the traces to the external components as
short as possible.
The electrical specification of the oscillator can be found in section 22.3.12. The oscillator cell is flexible and can
operate with a range of commonly available 32.768kHz crystals with load capacitances from 6 to 12.5pF. However,
the maximum ESR of the crystal and the supply current are both functions of the actual crystal used, see appendix
B.1 for more details.
5.2.3 32kHz External Clock
An externally supplied 32kHz reference clock on the 32KIN input (DIO9) may be provided to the JN5148. This would
allow the 32kHz system clock to be sourced from a very stable external oscillator module, allowing more accurate
sleep cycle timings compared to the internal RC oscillator. (See section 22.2.3 I/O Characteristics, DIO9 is a 3V
tolerant input)
20
•
•
•
32kHz RC Oscillator
32kHz Crystal Oscillator
32kHz External Clock
32KXTALIN
Figure 10: 32kHz crystal oscillator connections
JN-DS-JN5148-001 1v6
32KXTALOUT
JN5148
© NXP Laboratories UK 2010