MAX7322 Maxim, MAX7322 Datasheet - Page 14

• Manufacturer Part Number: MAX7322
• Description: The MAX7322 2-wire serial-interfaced peripheral features four push-pull outputs and four input ports with selectable internal pullups
• Manufacturer: Maxim

I
4 Push-Pull Outputs and 4 Inputs
Each of the four output ports O0, O1, O6, and O7 has
protection diodes to V+ and to GND
port output is driven to a voltage lower than GND, the
appropriate protection diode clamps the output to a
diode drop above V+ or below GND. When the
MAX7322 is powered down (V+ = 0), each output port
appears as a diode clamp to GND (Figure 9).
Each of the four input ports I2–I5 has a protection diode
to GND (Figure 10). When a port input is driven to a
voltage lower than GND, the protection diode will
clamp the input to a diode drop below GND.
Each of the four inputs ports I2–I5 also has a 40kΩ (typ)
pullup resistor that can be enabled or disabled. When a
port is driven to a voltage higher than V+, the body
diode of the pullup enable switch conducts and the
40kΩ pullup resistor is enabled. When the MAX7322 is
powered down (V+ = 0), each input port appears as a
40kΩ pullup resistor in series with a diode connected to
zero. Input ports are protected to +6V under any of
these circumstances (Figure 10).
When driving LEDs from one of the four output ports
O0, O1, O6, or O7, a resistor must be connected in
series with the LED to limit the LED current to no more
than 20mA. Connect the LED cathode to the MAX7322
port, and the LED anode to V+ through the series cur-
rent-limiting resistor, R
light the LED. Choose the resistor value according to
the following formula:
where:
R
LED (Ω).
V
LED (V).
V
V
sinking I
I
For example, to operate a 2.2V red LED at 10mA from a
+5V supply:
The MAX7322 can be used to drive loads, such as
relays, that draw more than 20mA by paralleling out-
puts. Use at least one output per 20mA of load current;
for example, a 5V 330mW relay draws 66mA, and
14
LED
LED
LED
OL
SUPPLY
2
Driving Load Currents Higher than 20mA
C Port Expander with
______________________________________________________________________________________
is the desired operating current of the LED (A).
is the output low voltage of the MAX7322 when
is the forward voltage of the LED (V).
is the resistance of the resistor in series with the
LED
R
R
is the supply voltage used to drive the
LED
LED
(V).
= (5 - 2.2 - 0.07) / 0.010 = 270Ω
= (V
SUPPLY
LED
. Set the port output low to
- V
LED
Driving LED Loads
- V
Port Structures
OL
(Figure 9). When a
) / I
LED
therefore, requires all four paralleled outputs. Any com-
bination of outputs can be used as part of a load-shar-
ing design, because any combination of ports can be
set or cleared at the same time by writing to the
MAX7322. Do not exceed a total sink current of 100mA
for the device.
The MAX7322 must be protected from the negative
voltage transient generated when switching off induc-
tive loads (such as relays), by connecting a reverse-
biased diode across the inductive load. Choose the
peak current for the diode to be greater than the induc-
tive load’s operating current.
The MAX7322 operates with a supply voltage of
+1.71V to +5.5V over the -40°C to +125°C temperature
range. Bypass the supply to GND with a ceramic
capacitor of at least 0.047µF as close to the device as
possible. For the TQFN version, additionally connect
the exposed pad to GND.
Figure 9. MAX7322 Push-Pull Output Port Structure
Figure 10. MAX7322 Input Port Structure
PULLUP
ENABLE
INPUT
OUTPUT
MAX7322
V+
Power-Supply Considerations
V+
V+
40kΩ
V+
MAX7322
PORTS
O0, O1, O6, O7
PORTS
I2–I5