CAT9557 Datasheet, PDF (8/17 Pages) ON Semiconductor – 8-Bit I2C-Bus and SMBus I/O Port

CAT9557
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_DD. The value of the pull−up resistor, R_P,
can be calculated based on minimum and maximum values
from Figures 7 and 8 (see Note 13).
RESET Input
A reset can be accomplished by holding the RESET pin
LOW for a minimum of tw(rst). The CAT9557 registers and
SMBus/I²C−bus state machine will be held in their default
state until the RESET input is once again HIGH. This input
requires a pull−up resistor to V_DD if no active connection is
used.
A0, A1, A2: Device Address Inputs
These inputs are used for extended addressing capability.
The A0, A1, A2 pins should be hardwired to V_DD or V_SS.
When hardwired, up to eight CAT9557s 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/O₀ to I/O₇: Input / Output Ports
Any of these pins may be configured as input or output.
The simplified schematic of I/O₀ is shown in Figure 3 and
the simplified schematic of I/O₁ to I/O₇ is shown in Figure 4.
When an I/O is configured as an input, the output transistor
Q2 from I/O₀ or the output transistors Q1 and Q2 from any
of the I/O₁ to I/O₇ are off for that particular I/O. If the I/O
pin is configured as an output, the open drain output stage of
I/O₀ or the push−pull output stage of I/O₁ to I/O₇ 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 between the pin and either V_DD or V_SS.
2.5
I_OL = 3 mA @ V_OLmax
2.0
1.5
1.0
0.5
0
2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6
V_DD, SUPPLY VOLTAGE (V)
Figure 7. Minimum R_P Value vs. Supply
Voltage
8
Fast Mode I²C Bus / tr max − 300 ns
7
6
5
4
3
2
1
0
0 50 100 150 200 250 300 350 400 450
C_BUS, BUS CAPACITANCE (pF)
Figure 8. Maximum R_P Value vs. Bus
Capacitance
13. According to the Fast Mode I²C bus specification, for bus capacitance up to 200 pF, the pull up device can be a resistor. For bus loads between
200 pF and 400 pF, the pull−up device can be a current source (I_max = 3 mA) or a switched resistor circuit.
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