Datasheet

LPC15XX All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
Product data sheet Rev. 1 — 19 February 2014 85 of 99
NXP Semiconductors
LPC15xx
32-bit ARM Cortex-M3 microcontroller
Remark: When a bus-powered circuit as shown in Figure 45 is used or, for a self-powered
device, when the VBUS pin is not connected, configure the PIO0_3/USB_VBUS pin for
GPIO (PIO0_3) in the IOCON block. This ties the VBUS signal HIGH internally.
14.1.1 USB Low-speed operation
The USB device controller can be used in low-speed mode supporting 1.5 Mbit/s data
exchange with a USB host controller.
Remark: To operate in low-speed mode, change the board connections as follows:
1. Connect USB_DP to the D- pin of the connector.
2. Connect USB_DM to the D+ pin of the connector.
External 10  resistors are recommended in low-speed mode to reduce over-shoots and
accommodate for 5 m cable length required for USB-IF testing.
14.2 XTAL input and crystal oscillator component selection
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 45. USB interface on a bus-powered device
REGULATOR
VBUS
LPC1xxx
V
DD
R1
1.5 kΩ
aaa-010821
USB-B
connector
USB_DP
USB_DM
V
SS
R
S
= 33 Ω
R
S
= 33 Ω
USB
USB_CONNECT