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:

where:

LED (

Ω).

For example, to operate a 2.2V red LED at 14mA from a

Ω.

Driving Load Currents Higher than 50mA

The MAX7313 can be used to drive loads drawing more

than 50mA, like relays and high-current white LEDs, by

paralleling outputs. Use at least one output per 50mA of

load current; for example, a 5V 330mW relay draws

66mA and needs two paralleled outputs to drive it.

Ensure that the paralleled outputs chosen are controlled

by the same blink phase register, i.e., select outputs

from the P0 through P7 range, or the P8 through P15

range. This way, the paralleled outputs are turned on

and off together. Do not use output O16 as part of a

load-sharing design. O16 cannot be switched at the

same time as any of the other outputs because it is con-

trolled by a different register.

The MAX7313 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 (Figure 18). The

peak current through the diode is the inductive load’s

operating current.

Power-Supply Considerations

The MAX7313 operates with a power-supply voltage of

2V to 3.6V. Bypass the power supply to GND with at

least 0.047µF as close to the device as possible.

For the QFN version, connect the underside exposed

pad to GND.

16-Port I/O Expander with LED Intensity

Control, Interrupt, and Hot-Insertion Protection

24

______________________________________________________________________________________

Figure 18. Diode-Protected Switching Inductive Load

MAX7313

P8

P10

P0

P1

P2

P3

P4

P5

P6

P7

V+

2V TO 3.6V

µC

SDA

SCL

SDA

I/O

AD0

P11

P12

P13

P14

P15

SCL

P9

GND

AD2

AD1

0.047

µF

INT/O16

BAS16

5V