MAX7325ATG Maxim Integrated, MAX7325ATG Datasheet - Page 15

• Manufacturer Part Number: MAX7325ATG
• Description: Interface - I/O Expanders
• Manufacturer: Maxim Integrated
• Series: MAX7325r

Specifications of MAX7325ATG

• Maximum Operating Frequency: 400 KHz
• Operating Supply Voltage: 1.71 V to 5.5 V
• Operating Temperature Range: - 40 C to + 125 C
• Package / Case: TQFN-24 EP
• Power Dissipation: 761.9 mW

diodes to V+ and GND continue to appear as a diode
clamp from each output to GND (Figure 10).
Each of the I/O ports P0–P7 has a protection diode to
GND (Figure 11). When a port is driven to a voltage
lower than GND, the protection diode clamps the port
to a diode drop below GND.
Each of the I/O ports P0–P7 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+, the
body diode of the pullup enable switch conducts and
the 40kΩ pullup resistor is enabled. When the
MAX7325 is powered down (V+ = 0V), each I/O port
appears as a 40kΩ resistor in series with a diode con-
nected to 0V. Input ports are protected to +6V under
any of these circumstances (Figure 11).
When driving LEDs from one of the outputs, a resistor
must be fitted in series with the LED to limit the LED
current to no more than 20mA. Connect the LED cath-
ode to the MAX7325 port, and the LED anode to V+
through the series current-limiting resistor, R
the port output low to illuminate the LED. Choose the
resistor value according to the following formula:
where:
R
LED (Ω).
V
(V).
Figure 10. MAX7325 Push-Pull Output Port Structure
Maxim Integrated
LED
SUPPLY
is the resistance of the resistor in series with the
OUTPUT
R
is the supply voltage used to drive the LED
LED
MAX7325
= (V
SUPPLY
GND
V+
- V
LED
V+
GND
I
Driving LED Loads
2
- V
C Port Expander with 8 Push-Pull
OL
) / I
O8–O15
LED
LED
. Set
V
V
sinking I
I
For example, to operate a 2.2V red LED at 10mA from a
+5V supply:
The MAX7325 can be used to drive loads, such as relays
that draw more than 20mA, by paralleling outputs. Use at
least one output per 20mA of load current; for example, a
5V 330mW relay draws 66mA, and therefore, requires
four paralleled outputs. Any combination of outputs can
be used as part of a load-sharing design because any
combination of ports can be set or cleared at the same
time by writing to the MAX7325. Do not exceed a total
sink current of 100mA for the device.
The MAX7325 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 inductive load’s operating current.
The MAX7325 operates with a supply voltage of +1.71V
to +5.5V. Bypass the supply to GND with a ceramic
capacitor of at least 0.047µF as close as possible to the
device. For the TQFN version, additionally connect the
exposed pad to GND.
Figure 11. MAX7325 Open-Drain I/O Port Structure
LED
LED
OL
and 8 Open-Drain I/Os
Driving Load Currents Higher than 20mA
is the desired operating current of the LED (A).
is the output low voltage of the MAX7325 when
OUTPUT
PULLUP
ENABLE
is the forward voltage of the LED (V).
INPUT
LED
R
LED
(V).
= (5 - 2.2 - 0.1) / 0.01 = 270Ω
V+
Power-Supply Considerations
V+
40kΩ
MAX7325
MAX7325
P0–P7
15