UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
47 of 362
NXP Semiconductors
UM10208
Chapter 6: LPC2800 DC-DC converter
3.3 Switching from battery power to USB power
shows the timing of the DC-DC Converter when powered by a battery supply,
and USB power is cycled. Note that timing and voltage levels are not to scale.
The figure shows the DC-DC running (due to a prior START) from battery power. USB
power is then applied, causing the DC-DC converters to be turned off, while power is
switched to use the output of the LDO regulators. USB power is always used preferentially
if it is available. When USB power is disconnected, a STOP is generated and the device
goes to the off state.
Fig 13. Internal DC-DC(2) USB powered (no battery present)
(internal
reset_n)
DCDC_V
DDO(1V8),
DCDC_V
DDO(3V3)
DCDC_V
USB
Supply_OK
STOP
~1ms
DCDC_V
BAT