MAX7324 Maxim, MAX7324 Datasheet - Page 15

• Manufacturer Part Number: MAX7324
• Description: The MAX7324 2-wire serial-interfaced peripheral features 16 I/O ports that are divided into eight push-pull outputs and eight inputs
• Manufacturer: Maxim

SDA, SCL, AD0, AD2, RST, INT, and I0–I7 are overvolt-
age protected to +6V. This allows the MAX7324 to
operate from a lower supply voltage, such as +3.3V,
while the I
ports are driven from a higher logic level, such as +5V.
The MAX7324 can operate from a higher supply volt-
age, such as +3V, while the I
of the input ports I0–I7 are driven from a lower logic
level, such as +2.5V. For V+ < 1.8V, apply a minimum
voltage of 0.8 x V+ to assert a logic-high on any input.
For V+ ≥ 1.8V, apply a voltage of 0.7 x V+ to assert a
logic-high. For example, a MAX7324 operating from a
+5V supply may not recognize a +3.3V nominal logic
high. One solution for input level translation is to drive
the MAX7324 inputs from open-drain outputs. Use a
pullup resistor to V+ or a higher supply to ensure a high
logic voltage greater than 0.7 x V+.
RST, SCL, SDA, AD0, and AD2 remain high impedance
with up to +6V asserted on them when the MAX7324 is
powered down (V+ = 0). The MAX7324 can therefore
be used in hot-swap applications.
Figure 11. MAX7324 Output Port Structure
I
2
C Port Expander with Eight Push-Pull Outputs
Port Output Signal Level Translation
OUTPUT
2
MAX7324
Port Input and I
C interface and/or any of the eight input
Translation from Higher or Lower
Applications Information
______________________________________________________________________________________
GND
V+
2
V+
C interface and/or some
GND
2
C Interface Level
Logic Voltages
O8–O15
Each of the eight output ports has protection diodes to
V+ and GND. When a port output is driven to a voltage
higher than V+ or lower than GND, the appropriate pro-
tection diode clamps the output to a diode drop above
V+ or below GND. When the MAX7324 is powered
down (V+ = 0), every output port's protection diodes to
V+ and GND continue to appear as a diode clamp from
each output to GND (Figure 11).
Each of the input ports I0–I7 has a protection diode to
GND (Figure 12). When a port input is driven to a volt-
age lower than GND, the protection diode clamps the
voltage to a diode drop below GND.
Each of the eight input ports I0–I7 also has a 40kΩ (typ)
pullup resistor that can be enabled or disabled. When a
port input is driven to a voltage higher than V+
body diode of the pullup enable switch conducts and
the 40kΩ pullup resistor is enabled. When the
MAX7324 is powered down (V+ = 0), every input port
appears as a 40kΩ resistor in series with a diode con-
nected to ground. Input ports are protected to +6V
under any of these circumstances.
When driving LEDs from one of the eight output ports,
O8–O15, a resistor must be fitted in series with the LED to
limit the LED current to no more than 20mA. Connect the
LED cathode to the MAX7324 port, and the LED anode
to V+ through the series current-limiting resistor, R
Figure 12. MAX7324 Input Port Structure
INPUT
ENABLE
PULLUP
and Eight Inputs
V+
V+
40kΩ
MAX7324
Driving LED Loads
I0–I7
,
LED
the
15
.