PAC5253 datasheet(49/68 Pages) ACTIVE-SEMI

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PAC5253

Power Application Controller

15.3. Functional Description

The PAC clock control system covers a wide range of applications.

15.3.1. Free Running Clock (FRCLK)

The free running clock (FRCLK) is generated from one of the 4 clock sources: ring oscillator, trimmed RC oscillator,

crystal driver or external clock input. The FRCLK is used for the real-time clock (RTC), watchdog timer (WDT), input to

the PLL, or FCLK source to clock the system in low power and sleep mode.

15.3.2. Fast Clock (FCLK)

The fast clock (FCLK) is generated from the PLL or supplied by the FRCLK directly. The FCLK supplies the watchdog

timer (WDT), ADC, wake-up interrupt controller (WIC), SysTick timer, ARM Cortex-M0 peripheral high speed clock

(HCLK) and low speed clock (LSCLK).

15.3.3. High-Speed Clock (HCLK)

The high-speed clock (HCLK) is derived from the FCLK with a /1, /2, /4 or /8 divider. It supplies the peripheral AHB/APB

bus, Timers A to D, dead-time controllers, SPI interface, I2C interface, UART interface, EMUX interface, SOC bridge

interface and memory subsystem, and can go as high as 50MHz.

15.3.4. Auxiliary Clock (ACLK)

The auxiliary clock (ACLK) is derived from FCLK with a /1, /2, to /128 divider, and supplies the timer and dead -time

blocks. It can be clocked faster or slower than HCLK and can go as high as 100MHz.

15.3.5. Clock Gating

The clock tree supports clock gating in deep-sleep mode for the timer block, ADC, SPI interface, I2C interface, UART

interface, memory subsystem and the ARM Cortex-M0 itself.

15.3.6. Ring Oscillator (ROSC)

The integrated ring oscillator provides 4 different clocks with 7.5MHz, 9.6MHz, 13.8MHz, and 25.7MHz settings. After

reset, the clock tree always defaults to this clock input with the lowest frequency setting.

15.3.7. Trimmed 4MHz RC Oscillator

The 1% trimmed 4MHz RC oscillator provides an accurate clock suitable for many applications. It is also used to derive the

clock for the Multi-Mode Power Manager.

15.3.8. Internal Slow RC Oscillator

An internal 32kHz RC oscillator is used during start up to provide an initial clock to analog circuitry. It is not used as a

clock input to the clock tree.

15.3.9. Crystal Oscillator Driver

The optional crystal oscillator driver can drive crystals from 2MHz to 10MHz to provide a highly accurate and stable clock

into the system.

15.3.10. External Clock Input

The clock tree can be supplied with an external clock up to 10MHz.

15.3.11. PLL

The integrated PLL input clock is supplied by the FRCLK with an input frequency range of 1MHz to 25MHz. The PLL

output frequency is adjustable from 3.5MHz to 100MHz.

- 49 -

Rev 1.10‒January 28, 2016

PAC5253 Datasheet(PDF) 49 Page - Active-Semi, Inc