Datasheet

LPC4350_30_20_10 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 4.2 — 18 August 2014 137 of 155
NXP Semiconductors
LPC4350/30/20/10
32-bit ARM Cortex-M4/M0 microcontroller
On the LPC4350/30/20/10, USBn_VBUS pins are 5 V tolerant only when VDDIO is
applied and at operating voltage level. Therefore, if the USBn_VBUS function is
connected to the USB connector and the device is self-powered, the USBn_VBUS pins
must be protected for situations when VDDIO = 0 V.
If VDDIO is always at operating level while VBUS = 5 V, the USBn_VBUS pin can be
connected directly to the VBUS pin on the USB connector.
For systems where VDDIO can be 0 V and VBUS is directly applied to the USBn_VBUS
pins, precautions must be taken to reduce the voltage to below 3.6 V, which is the
maximum allowable voltage on the USBn_VBUS pins in this case.
One method is to use a voltage divider to connect the USBn_VBUS pins to VBUS on the
USB connector. The voltage divider ratio should be such that the USB_VBUS pin will be
greater than 0.7VDDIO to indicate a logic HIGH while below the 3.6 V allowable maximum
voltage.
For the following operating conditions
VBUS
max
= 5.25 V
VDDIO = 3.6 V,
the voltage divider should provide a reduction of 3.6 V/5.25 V or ~0.686 V.
For bus-powered devices, a regulator powered by USB can provide 3.3 V to VDDIO
whenever bus power is present and ensure that power to the USBn_VBUS pins is always
present when the 5 V VBUS signal is applied. See Figure 48
.
Remark: Applying 5 V to the USBn_VBUS pins for a short time while the regulator ramps
up might compromise the long-term reliability of the part but does not affect its function.
Fig 47. USB interface on a self-powered device where USBn_VBUS = 5 V
LPC43xx
VDDIO
USB-B
connector
USBn_VBUS
VBUS
USB
R2
R3
aaa-013458