CPC5903

12

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R02

For the bidirectional buffer, it is necessary to configure

the IOB bus to be compatible with the CPC5903’s

lower logic low input threshold:

As discussed earlier, this lower input threshold

requirement is to ensure the CPC5903 can drive a

devices on the bus, but will not accept it’s own logic

low output. This prevents latching of the CPC5903.

Additionally, this implies there can be no more than

one limited drive (Side B) CPC5903 interface on the

IOB bus, and that all other devices on the bus must

Because the CPC5903 Side A inputs are compatible

with this requirement, any number of CPC5903 Side A

devices may be connected to the Side B bus.

For all modes, the minimum required voltage drop

which gives the calculation for the minimum value of

the pull-up resistor as:

the non-CPC5903 bus drivers.

For Standard-mode designs, with output drivers rated

at 3mA and a maximum supply voltage of 3.6V, the

minimum value of the pull-up resistor is:

The minimal standard value 1% resistor with a

100ppm/

C temperature coefficient that will not go

below the calculated minimum due to tolerance and

temperature is 1k

.

In Fast-mode designs with 6mA capable output drivers

and a supply voltage maximum of 5.5V, the minimum

Fast-mode pull-up resistor value is calculated to be:

For a Fast-mode design with high capacitive bus

loading, a 768

, 1%, 100ppm/C resistor would

suffice. When the bus does not have a heavy

capacitive load, a larger value pull-up resistor can be

used thereby reducing overall power consumption.