Datasheet
Applications Information
Hot Insertion
I/O ports P0–P15, interrupt output INT/O16, RST input,
BLINK input, and serial interface SDA, SCL, AD0 remain
high impedance with up to 6V asserted on them when
the MAX7314 is powered down (V+ = 0V). The MAX7314
can therefore be used in hot-swap applications.
Output Level Translation
The open-drain output architecture allows the ports to
level translate the outputs to higher or lower voltages
than the MAX7314 supply. An external pullup resistor
can be used on any output to convert the high-imped-
ance logic-high condition to a positive voltage level.
The resistor can be connected to any voltage up to
5.5V. For interfacing CMOS inputs, a pullup resistor
value of 220kΩ is a good starting point. Use a lower
resistance to improve noise immunity, in applications
where power consumption is less critical, or where a
faster rise time is needed for a given capacitive load.
Driving LED Loads
When driving LEDs, a resistor in series with the LED
must be used to limit the LED current to no more than
50mA. Choose the resistor value according to the fol-
lowing formula:
R
LED
= (V
SUPPLY
- V
LED
- V
OL
) / I
LED
where:
R
LED
is the resistance of the resistor in series with the
LED (Ω).
V
SUPPLY
is the supply voltage used to drive the LED (V).
V
LED
is the forward voltage of the LED (V).
V
OL
is the output low voltage of the MAX7314 when
sinking I
LED
(V).
I
LED
is the desired operating current of the LED (A).
For example, to operate a 2.2V red LED at 14mA from a
5V supply, R
LED
= (5 - 2.2 - 0.25) / 0.014 = 182Ω.
MAX7314
18-Port GPIO with LED Intensity Control,
Interrupt, and Hot-Insertion Protection
______________________________________________________________________________________ 19
Table 12. PWM Intensity Settings (Blink Enabled)
EXAMPLES OF LED BLINK BEHAVIOR
(LED IS ON WHEN OUTPUT IS LOW)
PWM DUTY CYCLE
OUTPUT BLINK
PHASE X
REGISTER BIT = 0
PWM DUTY CYCLE
OUTPUT BLINK
PHASE X
REGISTER = 1
OUTPUT
(OR
GLOBAL)
INTENSITY
SETTING
LOW
TIME
HIGH
TIME
LOW
TIME
HIGH
TIME
BLINK PHASE 0
REGISTER BIT = 0
BLINK PHASE 1
REGISTER BIT = 1
BLINK PHASE 0
REGISTER BIT = 1
BLINK PHASE 1
REGISTER BIT = 0
0x0 1/16 15/16 15/16 1/16
0x1 2/16 14/16 14/16 2/16
0x2 3/16 13/16 13/16 3/16
0x3 4/16 12/16 12/16 4/16
0x4 5/16 11/16 11/16 5/16
0x5 6/16 10/16 10/16 6/16
0x6 7/16 9/16 9/16 7/16
P hase 0: LE D on at l ow i ntensi ty
P hase 1: LE D on at hi g h i ntensi ty
P hase 0: LE D on at hi g h i ntensi ty
P hase 1: LE D on at l ow i ntensi ty
0x7 8/16 8/16 8/16 8/16 Output is half intensity during both blink phases
0x8 9/16 7/16 7/16 9/16
0x9 10/16 6/16 6/16 10/16
0xA 11/16 5/16 5/16 11/16
0xB 12/16 4/16 4/16 12/16
0xC 13/16 3/16 3/16 13/16
0xD 14/16 2/16 2/16 14/16
0xE 15/16 1/16 1/16 15/16
P hase 0: LE D on at hi g h i ntensi ty
P hase 1: LE D on at l ow i ntensi ty
P hase 0: LE D on at l ow i ntensi ty
P hase 1: LE D on at hi g h i ntensi ty
0xF Static low Static low
Static high
impedance
Static high
impedance
Phase 0: LED on continuously
Phase 1: LED off continuously
Phase 0: LED off continuously
Phase 1: LED on continuously