Datasheet

LPC11U1X All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 2.2 — 11 March 2014 53 of 72
NXP Semiconductors
LPC11U1x
32-bit ARM Cortex-M0 microcontroller
For a bus-powered device, the VBUS signal does not need to be connected to the
USB_VBUS pin (see Figure 27
). The USB_CONNECT function can additionally be
connected as shown in Figure 26
to prevent the USB from timing out when there is a
significant delay between power-up and handling USB traffic.
Remark: When a bus-powered circuit as shown in Figure 27 is used, configure the
PIO0_3/USB_VBUS pin for GPIO (PIO0_3) in the IOCON block to ensure that the
USB_CONNECT
signal can still be controlled by software. For details on the soft-connect
feature, see the LPC11U1x user manual (Ref. 1
).
Remark: When a self-powered circuit is used without connecting VBUS, configure the
PIO0_3/USB_VBUS pin for GPIO (PIO0_3) and provide software that can detect the host
presence through some other mechanism before enabling USB_CONNECT
and the
soft-connect feature. Enabling the soft-connect without host presence will lead to USB
compliance failure.
11.2 XTAL input
The input voltage to the on-chip oscillators is limited to 1.8 V. If the oscillator is driven by a
clock in slave mode, it is recommended that the input be coupled through a capacitor with
C
i
= 100 pF. To limit the input voltage to the specified range, choose an additional
capacitor to ground C
g
which attenuates the input voltage by a factor C
i
/(C
i
+ C
g
). In slave
mode, a minimum of 200 mV(RMS) is needed.
Fig 27. USB interface on a bus-powered device
LPC1xxx
V
DD
R1
1.5 kΩ
aaa-010179
USB-B
connector
USB_DP
USB_DM
V
SS
R
S
= 33 Ω
R
S
= 33 Ω
REGULATOR
VBUS