[Ovmsdev] OVMS CAN-USB Call for Assistance
s2000 at sounds.wa.com
Thu Sep 5 04:01:01 HKT 2013
The MCP2551 requires a minimum Vdd of 4.5V to ensure ISO-11898
specifications, but USB Vbus is only guaranteed to be 4.01V under
certain conditions like at the end of a bus-powered hub.
There are small 5V boost regulators that work with minimal passives,
some even with just capacitors and no inductors, but it will add to
the size and cost.
Maybe the SN65HVD233 is a better choice. It only tolerates 36V
spikes, not 42V, but I have no idea how likely either of those high
voltages are on a CAN bus in real vehicles.
The SN65HVD233 will tolerate 7V on Vcc, but 3.6V is the maximum
recommended. I almost suggested that it should run directly from USB
Vbus, but that is perhaps not wise. I'm sure the 3.3V LDO will handle
the load of the CPU and CAN transceiver.
On Sep 4, 2013, at 06:49, Mark Webb-Johnson wrote:
> I'm used to the mcp2551, but it is a 5V device. The pic32mx795 has
> both CAN port pins 5V tolerant, and levels for tx seem sufficient
> for mcp2551 to rx. The 5V is not too much of an issue, as we have
> that from USB, but it would be good to be just 3.3V.
> Anyone know of a 3.3V equivalent to the mcp2551? SN65HVD233? Or,
> just stay with mcp2551?
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