Datasheet

LPC178X_7X All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 5 — 9 September 2014 66 of 122
NXP Semiconductors
LPC178x/7x
32-bit ARM Cortex-M3 microcontroller
The first option assumes that power consumption is not a concern and the design ties the
V
DD(3V3)
and V
DD(REG)(3V3)
pins together. This approach requires only one 3.3 V power
supply for both pads, the CPU, and peripherals. While this solution is simple, it does not
support powering down the I/O pad ring “on the fly” while keeping the CPU and
peripherals alive.
The second option uses two power supplies; a 3.3 V supply for the I/O pads (V
DD(3V3)
) and
a dedicated 3.3 V supply for the CPU (V
DD(REG)(3V3)
). Having the on-chip voltage regulator
powered independently from the I/O pad ring enables shutting down of the I/O pad power
supply “on the fly” while the CPU and peripherals stay active.
The VBAT pin supplies power only to the RTC domain. The RTC operates at very low
power, which can be supplied by an external battery. The device core power
(V
DD(REG)(3V3)
) is used to operate the RTC whenever V
DD(REG)(3V3)
is present. There is no
power drain from the RTC battery when V
DD(REG)(3V3)
is at nominal levels and
V
DD(REG)(3V3)
> V
BAT
.
Fig 8. Power distribution
REAL-TIME CLOCK
BACKUP REGISTERS
REGULATOR
32 kHz
OSCILLATOR
POWER
SELECTOR
ULTRA-LOW
POWER
REGULATOR
RTC POWER DOMAIN
MAIN POWER DOMAIN
002aaf530
RTCX1
VBAT
(typical 3.0 V)
V
DD(REG)(3V3)
(typical 3.3 V)
RTCX2
V
DD(3V3)
V
SS
to memories,
peripherals,
oscillators,
PLLs
to core
to I/O pads
ADC
DAC
ADC POWER DOMAIN
V
DDA
VREFP
V
SSA
LPC178x/7x