
LPC2478
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 NXP B.V. 2011. All rights reserved.
Product data sheet
Rev. 3 — 12 September 2011 
47 of 93
NXP Semiconductors
LPC2478
Single-chip 16-bit/32-bit microcontroller
7.26.4
Power control
The LPC2478 supports a variety of power control features. There are four special modes 
of processor power reduction: Idle mode, Sleep mode, Power down-mode and Deep 
power-down mode. The CPU clock rate may also be controlled as needed by changing 
clock sources, reconfiguring PLL values, and/or altering the CPU clock divider value. This 
allows a trade-off of power versus processing speed based on application requirements. 
In addition, Peripheral power control allows shutting down the clocks to individual on-chip 
peripherals, allowing fine tuning of power consumption by eliminating all dynamic power 
use in any peripherals that are not required for the application. Each of the peripherals 
has its own clock divider which provides even better power control.
The LPC2478 also implements a separate power domain in order to allow turning off 
power to the bulk of the device while maintaining operation of the RTC and a small SRAM, 
referred to as the Battery RAM.
7.26.4.1
Idle mode
In Idle mode, execution of instructions is suspended until either a Reset or interrupt 
occurs. Peripheral functions continue operation during Idle mode and may generate 
interrupts to cause the processor to resume execution. Idle mode eliminates dynamic 
power used by the processor itself, memory systems and related controllers, and internal 
buses.
7.26.4.2
Sleep mode
In Sleep mode, the oscillator is shut down and the chip receives no internal clocks. The 
processor state and registers, peripheral registers, and internal SRAM values are 
preserved throughout Sleep mode and the logic levels of chip pins remain static. The 
output of the IRC is disabled but the IRC is not powered down for a fast wake-up later. The 
32 kHz RTC oscillator is not stopped because the RTC interrupts may be used as the 
wake-up source. The PLL is automatically turned off and disconnected. The CCLK and 
USB clock dividers automatically get reset to zero.
The Sleep mode can be terminated and normal operation resumed by either a Reset or 
certain specific interrupts that are able to function without clocks. Since all dynamic 
operation of the chip is suspended, Sleep mode reduces chip power consumption to a 
very low value. The flash memory is left on in Sleep mode, allowing a very quick wake-up.
On the wake-up from Sleep mode, if the IRC was used before entering Sleep mode, the 
code execution and peripherals activities will resume after 4 cycles expire. If the main 
external oscillator was used, the code execution will resume when 4096 cycles expire.
The customers need to reconfigure the PLL and clock dividers accordingly.
7.26.4.3
Power-down mode
Power-down mode does everything that Sleep mode does, but also turns off the IRC 
oscillator and the flash memory. This saves more power, but requires waiting for 
resumption of flash operation before execution of code or data access in the flash memory 
can be accomplished.
On the wake-up from Power-down mode, if the IRC was used before entering 
Power-down mode, it will take IRC 60
 
s to start-up. After this 4 IRC cycles will expire 
before the code execution can then be resumed if the code was running from SRAM. In