LPC MicrocontrollersのトピックRe: LPC4370 / Is it possible to apply a specified voltage to the USB pin when the device power is off?

LPC4370 / Is it possible to apply a specified voltage to the USB pin when the device power is off?

yasushihasegawa — Mon, 16 Jan 2017 09:51:12 GMT

Dear All,

Our device is implemented with LPC 4370.
There is a question about the case where our device is not powered on and voltage is supplied from the target host side via the USB cable.

[Background]
(1) Our device is a USB device, not a host.
(2) Our device is "self-powered device", not "bus-powered device".
(3) The other USB host device and our device are connected by a USB cable, and a voltage within the specified range is supplied to the USB cable from the USB Host device.

[conditions]
(1) The device power supply is OFF, and the following pins of LPC4370 are not powered.

VDD (IO)
VDD (REG) (3 V 3)
VDDA (3 V 3)
USB0_VDDA3V_DRIVER
USB 0 _ VDDA 3 V 3
Vprog (pf)

(2)Voltage is applied to our device from the other host's side via the USB cable under the above conditions.

[Question]
Is there a problem in applying a voltage within the specified range to the following USB pins of LPC 4370?
In other words, will internal latch-up and malfunctions not occur?

Pin name / specified range
USB0_VBUS / min 0[V], max 3.6[V]
USB0_DP / min 0[V], max 3.6[V]
USB0_DM / min 0[V], max 3.6[V]
USB0_ID / min 0[V], max 3.6[V]

Best Regards,
Yasushi

Re: LPC4370 / Is it possible to apply a specified voltage to the USB pin when the device power is off?

soledad — Wed, 25 Jan 2017 00:42:01 GMT

Hi,

The data sheet provides absolute max rates for a scenario similar to yours (Vddio=0v) as it is specified in table 10.

so you shouldn't have issues if you are careful with voltage spikes when restoring the supply to the device.

Have a great day,
Sol

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Re: LPC4370 / Is it possible to apply a specified voltage to the USB pin when the device power is off?

yasushihasegawa — Fri, 27 Jan 2017 12:42:48 GMT

Dear Soledad,

Thank you for your support.
I satisfy with your answer and advice.

Best Regards,
Yasushi Hasegawa