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 52 of 72
NXP Semiconductors
LPC11U1x
32-bit ARM Cortex-M0 microcontroller
11. Application information
11.1 Suggested USB interface solutions
The USB device can be connected to the USB as self-powered device (see Figure 26) or
bus-powered device (see Figure 27
).
On the LPC11U1x, the PIO0_3/USB_VBUS pin is 5 V tolerant only when V
DD
is applied
and at operating voltage level. Therefore, if the USB_VBUS function is connected to the
USB connector and the device is self-powered, the USB_VBUS pin must be protected for
situations when V
DD
= 0 V.
If V
DD
is always greater than 0 V while VBUS = 5 V, the USB_VBUS pin can be connected
directly to the VBUS pin on the USB connector.
For systems where V
DD
can be 0 V and VBUS is directly applied to the VBUS pin,
precautions must be taken to reduce the voltage to below 3.6 V, which is the maximum
allowable voltage on the USB_VBUS pin in this case.
One method is to use a voltage divider to connect the USB_VBUS pin to the VBUS on the
USB connector. The voltage divider ratio should be such that the USB_VBUS pin will be
greater than 0.7V
DD
to indicate a logic HIGH while below the 3.6 V allowable maximum
voltage.
For the following operating conditions
VBUS
max
= 5.25 V
V
DD
= 3.6 V,
the voltage divider should provide a reduction of 3.6 V/5.25 V or ~0.686 V.
Fig 26. USB interface on a self-powered device where USB_VBUS = 5 V
LPC1xxx
USB-B
connector
USB_DP
USB_CONNECT
soft-connect switch
USB_DM
USB_VBUS
V
SS
V
DD
R1
1.5 kΩ
R
S
= 33 Ω
aaa-010178
R
S
= 33 Ω
R2
R3