MAX7315 Ver la hoja de datos (PDF) - Maxim Integrated

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MAX7315

8-Port I/O Expander with LED Intensity Control, Interrupt, and Hot-Insertion Protection

Maxim Integrated 

8-Port I/O Expander with LED Intensity

Control, Interrupt, and Hot-Insertion Protection

where:

RLED is the resistance of the resistor in series with the

LED (Ω).

VSUPPLY is the supply voltage used to drive the LED (V).

VLED is the forward voltage of the LED (V).

VOL is the output low voltage of the MAX7315 when

sinking ILED (V).

ILED is the desired operating current of the LED (A).

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

5V supply, RLED = (5 - 2.2 - 0.25) / 0.014 = 182Ω.

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

Table 12. PWM Intensity Settings (Blink Enabled)

OUTPUT

(OR

GLOBAL)

INTENSITY

SETTING

0x0

0x1

0x2

0x3

0x4

0x5

0x6

0x7

0x8

0x9

0xA

0xB

0xC

0xD

0xE

0xF

PWM DUTY CYCLE

OUTPUT BLINK

PHASE X

REGISTER BIT = 0

PWM DUTY CYCLE

OUTPUT BLINK

PHASE X

REGISTER BIT = 1

EXAMPLES OF LED BLINK BEHAVIOR

(LED IS ON WHEN OUTPUT IS LOW)

BLINK PHASE 0

REGISTER BIT = 0

BLINK PHASE 0

REGISTER BIT = 1

LOW

TIME

1/16

2/16

3/16

4/16

5/16

6/16

7/16

8/16

9/16

10/16

11/16

12/16

13/16

14/16

15/16

Static low

HIGH

TIME

LOW

TIME

HIGH

TIME

BLINK PHASE 1

REGISTER BIT = 1

BLINK PHASE 1

REGISTER BIT = 0

15/16

15/16

1/16

14/16

14/16

2/16

13/16

12/16

11/16

13/16

12/16

11/16

3/16

Phase 0: LED on at low intensity Phase 0: LED on at high intensity

4/16

Phase 1: LED on at high intensity Phase 1: LED on at low intensity

5/16

10/16

10/16

6/16

9/16

9/16

7/16

8/16

8/16

8/16

Output is half intensity during both blink phases

7/16

7/16

9/16

6/16

6/16

10/16

5/16

5/16

11/16

Phase 0: LED on at high intensity Phase 0: LED on at low intensity

4/16

4/16

12/16

Phase 1: LED on at low intensity Phase 1: LED on at high intensity

3/16

3/16

13/16

2/16

2/16

14/16

1/16

1/16

15/16

Static high Static high Phase 0: LED on continuously Phase 0: LED off continuously

Static low

impedance impedance Phase 1: LED off continuously Phase 1: LED on continuously

20 ______________________________________________________________________________________

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