Wide Brightness Range

CCFL Backlight Controllers

24

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Status Register

[STATUS1–STATUS0] (POR = 0b11)

The status register returns information on fault condi-

tions. If a lamp is not connected to the secondary of the

transformer, the MAX1739 will detect that the lamp cur-

rent has not exceeded the CSAV detection threshold

and after 2 seconds will clear the STATUS1 bit (see

Lamp-Out Detection). The STATUS1 bit is latched; i.e.,

it will remain 0 even if the lamp-out condition goes

away. When STATUS1 = 0, the lamp is forced off. STA-

TUS0 reports 1 as long as no overcurrent conditions

are detected. If an overcurrent condition is detected in

any given DPWM period, STATUS0 is cleared for the

duration of the following DPWM period. If an overcur-

rent condition is not detected in any given DPWM peri-

od, STATUS0 is set for the duration of the following dig-

ital DPWM period. Forcing the CCFL lamp off by

entering shutdown, writing to the mode register, or by

toggling SH/SUS sets STATUS1.

ID Registers

The ID registers return information on the manufacturer,

the chip ID, and the chip revision number. The

MAX1739 is the first-generation advanced CCFL con-

troller, and its ChipRev is 0x00. Reading from the MfgID

register returns 0x4D, which is the ASCII code for “M”

(for Maxim); the ChipID register returns 0x96. Writing to

these registers has no effect.

BIT

NAME

POR

STATE

DESCRIPTION

2

SHMD2

0

SHMD2 = 1 forces the lamp off and sets STATUS1. SHMD2 = 0 allows the lamp to operate, though it

may still be shut down by the SH/SUS pin (depending on the state of SHMD1 and SHMD0).

1

SHMD1

0

When SH /SUS = 0, this bit has no effect. SH/SUS = 1 and SHMD1 = 1 forces the lamp off and sets

STATUS1. SH /SUS = 1 and SHMD1 = 0 allow the lamp to operate, though it may still be shut down

by the SHMD2 bit.

0

SHMD0

1

When SH /SUS = 1, this bit has no effect. SH /SUS = 0 and SHMD0 = 1 forces the lamp off and sets

STATUS1. SH /SUS = 0 and SHMD0 = 0 allows the lamp to operate, though it may still be shut down

by the SHMD2 bit.

Table 7. SHMD Register Bit Descriptions

SH/SUS

SHMD2

SHMD1

SHMD0

OPERATING MODE

0

0

X

0

Operate

0

0

X

1

Shutdown, STATUS1 set

1

0

0

X

Operate

1

0

1

X

Shutdown, STATUS1 set

X

1

X

X

Shutdown, STATUS1 set

Table 8.

SH/SUS and SHMD Register Truth Table

BIT

NAME

POR

STATE

DESCRIPTION

1

STATUS1

1

STATUS1 = 0 means that a lamp-out condition has been detected. The STATUS1 bit stays clear

even after the lamp-out condition has gone away. The only way to set STATUS1 is to shut off the

lamp by programming the mode register or by toggling SH/SUS.

0

STATUS0

1

STATUS0 = 0 means that an overcurrent condition was detected during the previous digital PWM

period. STATUS0 = 1 means that no overcurrent condition was detected during the previous digital

PWM period.

Table 9. Status Register Bit Descriptions (Read Only/Writes Have No Effect)

X = Don’t care