UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
42 of 362
1.
Overview
The LPC288x includes an on-chip power system which allows the device to be powered
by a standard single cell battery (AA or AAA for example), as well as from a USB port or
other power source.
The LPC288x needs two supply voltages, 3.3V and 1.8V, for various internal functions.
When power is available from a higher voltage source such as USB, two internal Low
Dropout regulators (LDO regulators) reduce the incoming voltage to those needed by the
LPC288x. When only a low voltage battery supply is available, two DC-DC converters
boost the voltage up to the needed levels. Switching between the two modes is supported.
For example, a handheld, battery powered device can be plugged into a USB port and
use that power while connected in order to save battery life. For the sake of brevity, the
entire power regulation system is referred to as the DC-DC converter.
UM10208
Chapter 6: DC-to-DC converter
Rev. 02 — 1 June 2007
User manual
Fig 9.
Block diagram of the DC-DC converter
DC-DC
Converter 1
DC-DC Controller
DCDC_V
BAT
LDO1
Linear Regulator 1
vin
vout
LDO2
Linear Regulator 1
vin
vout
DCDC_V
USB
5V
DCDC_V
DDO(3v3)
DCDC_V
DDO(1v8)
Local
Power
Low Voltage
Bandgap
Ring Osc.
vref
DC-DC Converter
Control Registers
3
3
12 MHz
(from crystal)
internal
reset
clock
control
power-on
reset
START
STOP
0.9V <
1.2V
< 1.6V
DC-DC
Converter 2
control to
DC-DC 2
control to
DC-DC 1
USB present