MAX6946CAWE+T Datasheet MAX6946ATE+, MAX6947ATE+, MAX6947ATE+T | P13-P15

Shutdown Mode

In shutdown mode, all ports configured as constant-

current outputs (output register set to a value between

0x02 and 0xFE) are switched off, and these outputs go

high impedance as if their registers were set to value

0xFF. Ports configured as logic inputs or outputs (out-

put registers set to value 0x00 or 0x01) are unaffected

(Table 4). This means that any ports used for GPIOs

are still fully operational in shutdown mode, and port

inputs can be read and output ports can be toggled at

any time using the serial interface. Use the MAX6946/

MAX6947 for a mix of logic inputs, logic outputs, and

PWM LED drivers, and only the LED drivers turn off

automatically in shutdown.

Put the MAX6946/MAX6947 into shutdown mode by

clearing the run bit (bit D0) in the configuration register

(0x10) (Table 2). Exit shutdown by setting the run bit high

through the serial interface or by using the Reset Run

option (see the Reset Run Option section). Configure

and control the MAX6946/MAX6947 normally through the

serial interface in shutdown mode. All registers are

accessible in shutdown mode, and shutdown mode

does not change any register values.

Changing a port from static logic-low (0x00) or static

logic-high (0x01) to a constant-current value

(0x02–0xFE) in shutdown mode turns that output off

(logic-high or high impedance) like any other constant-

current outputs in shutdown. The new constant-current

output starts just like any other constant-current outputs

when exiting shutdown.

Changing a port from a constant-current value

(0x02–0xFE) to static logic-low (0x00) or static logic-

high (0x01) in shutdown causes that output to set to the

value as a GPIO output. The new GPIO output is unaf-

fected just like any other GPIO output when exiting

shutdown.

Ramp-Up and Ramp-Down Controls

The MAX6946/MAX6947 provide controls that allow the

output currents to ramp down into shutdown (ramp-

down), and ramp up again out of shutdown (ramp-up)

(Figures 4 and 5). Ramp-down comprises a programma-

ble hold-off delay that also maintains the outputs at full

current for a time before the programmed fade-off time.

After the hold-off delay, the output currents ramp down.

MAX6946/MAX6947

10-Port, Constant-Current LED Driver and

I/O Expander with PWM Intensity Control

______________________________________________________________________________________ 13

EXIT SHUTDOWN COMMAND

FULL CURRENT/

HALF CURRENT

1s 2s1/4s 1/2s

1/8s

1/16s

ZERO TO 4s CURRENT RAMP-UP AFTER CS RUN

Figure 4. Ramp-Up Behavior

ZERO TO 4s HOLD-OFF DELAY BEFORE FADE-OFF

ZERO TO 4s CURRENT FADE-OFF AFTER HOLD-OFF DELAY

1s 2s 4s 1s 2s

1/8s

1/16s

1/8s

1/16s

ZERO TO 8s CURRENT RAMP-DOWN

4s1/4s 1/2s 1/4s 1/2s

FULL CURRENT/

HALF CURRENT

Figure 5. Ramp-Down, Hold-Off, and Fade-Off Behavior

MAX6946/MAX6947

The ramp-down register sets the hold-off and fade-off

times and allows disabling of hold-off and fade-off (zero

delay), if desired (Table 8). The ramp-up register sets

the ramp-up time and allows disabling of ramp-up (zero

delay), if desired (Table 9). The configuration register

contains three status bits that identify the condition of

the MAX6946/MAX6947, hold-off, fade-off, or ramp-up

(Table 2). The configuration register also enables or dis-

ables ramp-up. One write command to the configuration

(using hold-off and fade-off settings in the fade register)

and one read command to the configuration register can

determine whether the Reset Run is enabled for restart,

and whether the MAX6946/MAX6947 will use ramp-up

on restart.

10-Port, Constant-Current LED Driver and

I/O Expander with PWM Intensity Control

14 ______________________________________________________________________________________

20mA

15mA

10mA

5mA

0mA

CURRENT

FADE-UP

FULL

CURRENT

7/8

CURRENT

6/8

CURRENT

5/8

CURRENT

4/8

CURRENT

3/8

CURRENT

2/8

CURRENT

1/8

CURRENT

ZERO

CURRENT

17.5mA

12.5mA

7.5mA

2.5mA

PORT CURRENT = HALF

FADE-OFF

PORT CURRENT = FULL

Figure 6. Output Fade DAC (Global Current = 0x07)

Table 8. Ramp-Down Register Format (0X11)

DESCRIPTION

D7 D6 D5 D4 D3 D2 D1

Instant going into shutdown after hold-off delay X X X X X 0 0 0

1/16s ramp-down from full current before shutdown after hold-off delay X X X X X 0 0 1

1/8s ramp-down from full current before shutdown after hold-off delay X X X X X 0 1 0

1/4s ramp-down from full current before shutdown after hold-off delay X X X X X 0 1 1

1/2s ramp-down from full current before shutdown after hold-off delay X X X X X 1 0 0

1s ramp-down from full current before shutdown after hold-off delay X X X X X 1 0 1

2s ramp-down from full current before shutdown after hold-off delay X X X X X 1 1 0

4s ramp-down from full current before shutdown after hold-off delay X X X X X 1 1 1

Zero hold-off delay before fade-off going into shutdown X X 0 0 0 X X X

1/16s hold-off delay before fade-off going into shutdown X X 0 0 1 X X X

1/8s hold-off delay before fade-off going into shutdown X X 0 1 0 X X X

1/4s hold-off delay before fade-off going into shutdown X X 0 1 1 X X X

1/2s hold-off delay before fade-off going into shutdown X X 1 0 0 X X X

1s hold-off delay before fade-off going into shutdown X X 1 0 1 X X X

2s hold-off delay before fade-off going into shutdown X X 1 1 0 X X X

4s hold-off delay before fade-off going into shutdown X X 1 1 1 X X X

Ramp-up and ramp-down use the PWM clock for tim-

ing. When using the external oscillator make sure the

oscillator runs until the end of the sequence. The inter-

nal oscillator always runs during a fade sequence, even

if none of the ports use PWM.

The ramp-up and ramp-down circuit operates a 3-bit

DAC. The DAC adjusts the internal current reference

used to set the constant-current outputs in a similar

manner to the global-current register (Table 5). The

MAX6946/MAX6947 scale the master current reference

so all output constant-current and PWM settings adjust

at the same ratio with respect to each other. This

means the LEDs always fade at the same rate even if

with different intensity settings.

The maximum port output current set by the global-cur-

rent register (Table 5) also sets the point during ramp-

down that the current starts falling, and the point during

ramp-up that the current stops rising. Figure 7 shows

the ramp waveforms that occur with different global-

current register settings.

Reset Run Option

The MAX6946/MAX6947 feature a Reset Run option so

that simply taking the RST input high brings the driver

out of shutdown in addition to its normal function of

enabling the MAX6946/MAX6947s’ I

C interface. This

provides an alternative method of bringing the driver

out of shutdown to writing to the configuration register

through the serial interface. The Reset Run timing uses

the PWM clock, either the internal nominal 32kHz oscil-

lator or a user-provided clock fed into the OSC input

(MAX6946 only).

After enabling the Reset Run option, the MAX6946/

MAX6947 use the rising edge on RST, followed by no

C interface activity to the MAX6946/MAX6947 for 128

to 129 periods of the PWM clock to trigger the Reset

Run option. If this timeout period elapses without the

MAX6946/MAX6947 acknowledging an I

C transaction,

the run bit (D0) in the configuration register sets, bring-

ing the driver out of shutdown and activating any pro-

grammed ramp-up. If RST pulses high for less than this

timeout period to trigger a Reset Run, the MAX6946/

MAX6947 ignore the pulse, and the MAX6946/MAX6947

continue to wait for a suitable trigger.

Cancel the Reset Run trigger by transmitting an I

communication to the MAX6946/MAX6947 before the

timeout period elapses. The trigger cancels when the

MAX6946/MAX6947 acknowledge the I

C transaction

MAX6946/MAX6947

10-Port, Constant-Current LED Driver and

I/O Expander with PWM Intensity Control

______________________________________________________________________________________ 15

20mA

15mA

10mA

5mA

0mA

CURRENT

FULL

CURRENT

7/8

CURRENT

6/8

CURRENT

5/8

CURRENT

4/8

CURRENT

3/8

CURRENT

2/8

CURRENT

1/8

CURRENT

ZERO

CURRENT

17.5mA

12.5mA

7.5mA

2.5mA

RAMP-UP

RAMP-DOWN

GLOBAL CURRENT = 0x07

GLOBAL CURRENT = 0x06

GLOBAL CURRENT = 0x05

GLOBAL CURRENT = 0x04

GLOBAL CURRENT = 0x03

GLOBAL CURRENT = 0x02

GLOBAL CURRENT = 0x01

GLOBAL CURRENT = 0x00

Figure 7. Global Current Modifies Fade Behavior

Table 9. Ramp-Up Register Format (0x12)

DESCRIPTION

D7 D6 D5 D4 D3 D2 D1 D0

Instant full current coming out from shutdown X X X X X 0 0 0

1/16s ramp-up to full current coming out from shutdown X X X X X 0 0 1

1/8s ramp-up to full current coming out from shutdown X X X X X 0 1 0

1/4s ramp-up to full current coming out from shutdown X X X X X 0 1 1

1/2s ramp-up to full current coming out from shutdown X X X X X 1 0 0

1s ramp-up to full current coming out from shutdown X X X X X 1 0 1

2s ramp-up to full current coming out from shutdown X X X X X 1 1 0

4s ramp-up to full current coming out from shutdown X X X X X 1 1 1

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24

MAX6946CAWE+T

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LED Lighting Drivers 10-Port Constant Current LED Driver

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MAX6946CAWE+T

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