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Product data sheet Rev. 1 — 19 February 2014 84 of 99

NXP Semiconductors

LPC15xx

32-bit ARM Cortex-M3 microcontroller

14. Application information

14.1 Suggested USB interface solutions

The USB device can be connected to the USB as self-powered device (see Figure 44) or

bus-powered device (see Figure 45

On the LPC15xx, the PIO0_3/USB_VBUS pin is 5 V tolerant only when V

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

= 0 V.

If V

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

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

to indicate a logic HIGH while below the 3.6 V allowable maximum

voltage.

For the following operating conditions

VBUS

max

= 5.25 V

= 3.6 V,

the voltage divider should provide a reduction of 3.6 V/5.25 V or ~0.686 V.

For a bus-powered device, the VBUS signal does not need to be connected to the

USB_VBUS pin (see Figure 45

). The USB_CONNECT function can additionally be

enabled internally by setting the DCON bit in the DEVCMDSTAT register to prevent the

USB from timing out when there is a significant delay between power-up and handling

USB traffic. External circuitry is not required for the USB_CONNECT functionality.

Fig 44. USB interface on a self-powered device where USB_VBUS = 5 V

LPC1xxx

1.5 kΩ

aaa-010820

USB-B

connector

USB_DP

USB_DM

USB_VBUS

= 33 Ω

USB

USB_CONNECT