CAT9555_08 Datasheet, PDF (7/17 Pages) Catalyst Semiconductor – 16-bit I2C and SMBus I/O Port with Interrupt

CAT9555
PIN DESCRIPTION
SCL: Serial Clock
The serial clock input clocks all data transferred into or
out of the device. The SCL line requires a pull-up resistor
if it is driven by an open drain output.
SDA: Serial Data/Address
The bidirectional serial data/address pin is used to
transfer all data into and out of the device. The SDA pin
is an open drain output and can be wire-ORed with other
open drain or open collector outputs. A pull-up resistor
must be connected from SDA line to V_CC. The value of
the pull-up resistor, Rp, can be calculated based on
minimum and maximum values from Figure 2 and Figure
3 (see Note).
A0, A1, A2: Device Address Inputs
These inputs are used for extended addressing capabil-
ity. The A0, A1, A2 pins should be hardwired to V_CC or
V_SS. When hardwired, up to eight CAT9555s may be
addressed on a single bus system. The levels on these
inputs are compared with corresponding bits, A2, A1,
A0, from the slave address byte.
I/O 0.0 to I/O 0.7, I/O 1.0 to I/O 1.7: Input / Output Ports
Any of these pins may be configured as input or output.
The simplified schematic of I/Os is shown in Figure 4.
When an I/O is configured as an input, the Q1 and Q2
output transistors are off creating a high impedance
input with a weak pull-up resistor (typical 100 kohm). If
the I/O pin is configured as an output, the push-pull
output stage is enabled. Care should be taken if an
external voltage is applied to an I/O pin configured as an
output due to the low impedance paths that exist be-
tween the pin and either V_CC or V_SS.
2.5
2
1.5
1
0.5
0
2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6
VCC (V)
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
50 100 150 200 250 300 350 400
CBUS (pF)
Figure 2. Minimum Rp as a Function of Supply
Voltage (I_OL = 3mA @ V_{OL max})
Figure 3. Maximum Rp Value versus Bus
Capacitance (Fast Mode I²C Bus / t_{r max} = 300ns)
Note: According to the Fast Mode I²C bus specification, for bus capacitance up to 200pF, the pull up device
can be a resistor. For bus loads between 200pF and 400pF, the pull-up device can be a current source
(Imax = 3mA) or a switched resistor circuit.
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
7
Doc. No. MD-9003, Rev. G