where:

LED (

Ω).

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

Ω.

Driving Load Currents Higher than 50mA

The MAX7315 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. This way, the paralleled

outputs are turned on and off together. Do not use out-

put O8 as part of a load-sharing design. O8 cannot be

switched at the same time as any of the other outputs

because it is controlled by a different register.

The MAX7315 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 MAX7315 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.

Chip Information

TRANSISTOR COUNT: 17,611

PROCESS: BiCMOS

8-Port I/O Expander with LED Intensity

Control, Interrupt, and Hot-Insertion Protection

20

______________________________________________________________________________________

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 BIT = 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

Phase 0: LED on at low intensity

Phase 1: LED on at high intensity

Phase 0: LED on at high intensity

Phase 1: LED on at low intensity

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

Phase 0: LED on at high intensity

Phase 1: LED on at low intensity

Phase 0: LED on at low intensity

Phase 1: LED on at high intensity

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