ISL78171 Datasheet, PDF (19/29 Pages) Intersil Corporation – 6-Channel, 50mA Automotive LED Driver with Ultra-high Dimming Ratio and Phase Shift Control

ISL78171
SMBus/I²C Communications
The ISL78171 can be controlled by SMBus/I²C for PWM or DC
dimming. Except when both the SDA and SCL input pins are tied
to ground, the LEDs are off by default and the user must use the
SMBus/I²C interface to turn them on. When both SDA and SCL are
instead shorted to ground, the LEDs turn on by default when the IC is
turned on, and the customer can use the ISL78171 without having
to control the SMBus/I²C interface. The switching frequency is fixed
at 600kHz if SMBus/I²C is not used.
Write Byte
The Write Byte protocol is only three bytes long. The first byte
starts with the slave address followed by the “command code,”
which translates to the “register index” being written. The third
byte contains the data byte that must be written into the register
selected by the “command code”. A shaded label is used on
cycles during which the slaved backlight controller “owns” or
“drives” the Data line. All other cycles are driven by the “host
master.”
Read Byte
Figure 32 shows that the four byte long Read Byte protocol starts
out with the slave address followed by the “command code”,
which translates to the “register index.” Subsequently, the bus
direction turns around with the re-broadcast of the slave address
with bit 0 indicating a read (“R”) cycle. The fourth byte contains
the data being returned by the backlight controller. That byte
value in the data byte reflects the value of the register being
queried at the “command code” index. Note the bus directions,
which are highlighted by the shaded label that is used on cycles
during which the slaved backlight controller “owns” or “drives”
the Data line. All other cycles are driven by the “host master.”
Slave Device Address
The slave address contains 7 MSB plus one LSB as R/W bit, but
these 8 bits are usually called Slave Address bytes. Figure 33
shows that the high nibble of the Slave Address byte is 0x5 or
0101b to denote the “backlight controller class.” Bit 3 in the
lower nibble of the Slave Address byte is 1. Bit 0 is always the
R/W bit, as specified by the SMBus/I²C protocol. Note: In this
document, the device address will always be expressed as a full
8-bit address instead of the shorter 7-bit address typically used in
other backlight controller specifications to avoid confusion.
Therefore, if the device is in the write mode where bit 0 is 0, the
slave address byte is 0x58 or 01011000b. If the device is in the
read mode where bit 0 is 1, the slave address byte is 0x59 or
01011001b.
SMBus/I²C Register Definitions
The backlight controller registers are Byte wide and accessible
via the SMBus/I²C Read/Write Byte protocols. Their bit
assignments are provided in the following sections with reserved
bits containing a default value of “0”.
MSB
LSB
0
1
0
1
1
0
0 R/W
DEVICE
IDENTIFIER
DEVICE
ADDRESS
FIGURE 33. SLAVE ADDRESS BYTE DEFINITION
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June 15, 2015