Rainbow Electronics MAX8759 - Manual (Page 20)

MAX8759
values. POR occurs when V CC rises above 1.75V (typ).
The UVLO occurs when V
CC
is below 4.2V (typ). The
MAX8759 disables both high-side and low-side switch
drivers below the UVLO threshold.
Low-Power Shutdown
The MAX8759 is placed into shutdown by clearing bit 0
of the device control register (0x01).When the
MAX8759 is shut down, all functions of the IC are
turned off except the 5.35V linear regulator. In shut-
down, the linear regulator output voltage drops to 4.5V
and the supply current is 6µA (typ). While in shutdown,
the fault latch is reset. The device can be reenabled by
setting bit 0 of the device control register to 1.
Ambient-Light-Sensor Supply Pin (VALS)
The MAX8759 provides the supply voltage of the ALS
through the VALS pin. VALS is internally connected to
the 5.35V linear regulator output through a p-channel
MOSFET. The p-channel MOSFET is turned on when the
MAX8759 is enabled and turned off when the part is dis-
abled. Bypass VALS to ground with a minimum 0.lµF
ceramic capacitor. Place the capacitor as close to the
ALS supply input as possible.
SMBus Interface (SDA, SCL)
The MAX8759 supports an SMBus-compatible 2-wire
digital interface. SDA is the bidirectional data line and
SCL is the clock line of the 2-wire interface correspond-
ing respectively to SMBDATA and SMBCLK lines of the
SMBus. SDA and SCL have Schmidt-triggered inputs
that can accommodate slow edges; however, the rising
and falling edges should still be faster than 1µs and
300ns, respectively. The MAX8759 uses the write-byte
and read-byte protocols (Figure 8). The SMBus proto-
cols are documented in System Management Bus
Specification
V1.08 and are available at
http://www.sbs-forum.org/.
The MAX8759 is a slave-only device and responds to
the 7-bit address 0b0101100. The read and write com-
mands can be distinguished by adding ONE more bit
(R/
W bit) to the end of the 7-bit slave address, with one
indicating read and zero indicating write. The MAX8759
has seven registers: a brightness control register
(0x00), a device control register (0x01), a fault/status
register (0x02), an identification register (0x03), an ALS
status register (0x04), an ALS low-limit register (0x05),
Low-Cost, SMBus, CCFL Backlight Controller
20 ______________________________________________________________________________________
1b
ACK
1b 7 BITS
ADDRESS ACK
1b
WR
8 BITS
DATA
1b
ACK
—
P
8 BITS —
S COMMAND
WRITE-BYTE FORMAT
RECEIVE-BYTE FORMAT
SLAVE ADDRESS DATA BYTE: DATA GOES INTO THE
REGISTER SET BY THE COMMAND BYTE
1b
ACK
1b 7 BITS
ADDRESS ACK
1b
WR
—
S
1b
ACK
8 BITS
DATA
7 BITS
ADDRESS
1b
RD
1b 8 BITS —
///
—
P S COMMAND
SLAVE ADDRESS
SLAVE ADDRESS COMMAND BYTE: SENDS COM-
MAND WITH NO DATA; USUALLY
USED FOR ONE-SHOT COMMAND
COMMAND BYTE: SELECTS
WHICH REGISTER YOU ARE
READING FROM SLAVE ADDRESS: REPEATED
DUE TO CHANGE IN DATA-
FLOW DIRECTION DATA BYTE: READS FROM THE
REGISTER SET BY THE COMMAND
BYTE
1b
ACK
7 BITS
ADDRESS
1b
RD
8 BITS
DATA
1b
///
—
P
—
S
DATA BYTE: READS DATA FROM THE
REGISTER COMMANDED BY THE
LAST READ-BYTE OR WRITE-BYTE
TRANSMISSION; ALSO USED FOR
SMBus ALERT RESPONSE RETURN
ADDRESS
S = START CONDITION SHADED = SLAVE TRANSMISSION WR = WRITE = 0
P = STOP CONDITION ACK = ACKNOWLEDGED = 0 RD = READ = 1
/// = NOT ACKNOWLEDGED = 1
1b
ACK
7 BITS
ADDRESS
1b
WR
8 BITS
COMMAND
1b
ACK
—
P
—
S
SEND-BYTE FORMAT
READ-BYTE FORMAT
Figure 8. SMBus Protocols
COMMAND BYTE: SELECTS
WHICH REGISTER YOU ARE
WRITING TO