Rainbow-electronics MAX6964 Manual do Utilizador descarregar pdf (Página 16)

Driving Load Currents Higher than 50mA

The MAX6964 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 6V 330mW relay draws 55mA

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 O0

through O7 range, or the O8 through O15 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 controlled by a different register.

The MAX6964 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 19). The

peak current through the diode is the inductive load’s

operating current.

Power-Supply Considerations

The MAX6964 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.

MAX6964

17-Output LED Driver/GPO

with Intensity Control

16 ______________________________________________________________________________________

Table 9. PWM Intensity Settings (Blink Disabled)

PWM DUTY CYCLE

OUTPUT BLINK PHASE 0

PWM DUTY CYCLE

OUTPUT BLINK PHASE 0

OUTPUT

(OR

GLOBAL)

INTENSITY

SETTING

LOW TIME HIGH TIME

LED BEHAVIOR WHEN

OUTPUT BLINK PHASE 0

(LED IS ON WHEN

OUTPUT IS LOW)

LOW TIME HIGH TIME

LED BEHAVIOR WHEN

OUTPUT BLINK PHASE 0

(LED IS ON WHEN

OUTPUT IS LOW)

0x0 1/16 15/16 Lowest PWM intensity 15/16 1/16 Highest PWM intensity

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

0x7 8/16 8/16 8/16 8/16

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

 Increasing PWM intensity

2/16 14/16

Increasing PWM intensity 

0xE 15/16 1/16 Highest PWM intensity 1/16 15/16 Lowest PWM intensity

0xF

Static low Static low

Full intensity, no PWM

(LED on continuously)

Static high

impedance

Static high

impedance

LED off continuously

Figure 19. Diode-Protected Switching Inductive Load

MAX6964

O10

V+

2V TO 3.6V

µC

SDA

SCL

BLINK

SDA

I/O

AD0

O11

O12

O13

O14

O15

SCL

I/O

GND

0.047µF

RST

MMTBT4148

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 22 23

17-Output LED Driver/GPO 1

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