LT3965/LT3965-1
16
39651fa
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APPLICATIONS INFORMATION
1) All Channel Mode (ACMODE) Command
The ACMODE write command (see Figure 6) is used to set
the ACMREG register bits (see Table 1) to control the eight
channel switches together. The command is two bytes
long. The first byte is the ACMODE device write address
and the second byte is the data byte to be written to the
ACMREG register.
The ACMODE read command (see Figure 7) is used to read
back the ACMREG register bits and to get the LED and
overheat fault conditions. The command is four bytes long.
The first byte is the ACMODE device read address followed
by three data bytes read respectively from the ACMREG
register, the OLFREG register and the SLFREG register.
The LT3965/LT3965-1 ACMODE device address is
010A
4
A
3
A
2
A
1
followed by an eighth bit which is a data
direction bit (R/W)—a 0 indicates a write transmission
(the master writes to the addressed LT3965/LT3965-1),
a 1 indicates a read transmission (the master reads from
the addressed LT3965/LT3965-1). A
4
A
3
A
2
A
1
is an input
logic value from the programmable address select pins
ADDR4, ADDR3, ADDR2 and ADDR1.
ACMODE Write Command Latency
The ACMODE write command can
be conveniently used
for
quick status control of the eight channel LEDs. Each
ACMODE write command is two bytes long and takes
about 47µs to transmit if 400kHz SCL clock is chosen.
The command latency between the STOP condition and
channel switching on (LED turning off) is about 0.3µs,
and the command latency between the STOP condition
and channel switching off (LED turning on) is about 1µs.
Therefore, the minimum time from initiating to executing
an ACMODE write command is about 48µs if 400kHz SCL
clock is used.
ACMODE Write Command and Simultaneous Channel
Switching
The ACMODE write command can control all 8 channels
to switch together. It is possible to switch all LEDs from
on/off to off/on simultaneously using a single ACMODE
write command. A fast LED driver can respond well to a
sudden output voltage change caused by simultaneous
channel switching. An LED driver with slower response
may trigger false faults due to large transients in the
string current. When working with a slow LED driver, you
should avoid sending an ACMODE write command which
can cause simultaneous channel switching. Instead you
can use multiple ACMODE write commands, and each of
them makes one channel switch at
a time.
2) Single Channel Mode (SCMODE) Command
The SCMODE write command is used for setting the ad
-
dressed channel SCMREG register bits to control the channel
switch and to set the channel LED fault detecting thresholds.
The SCMODE write command has two formats: short for
-
mat (see Figure 8) and long format (see Figure 9). Both the
formats configure the channel SCMREG register. Choosing
the short format or the long format depends on which bits
of the channel SCMREG register you want to configure.
The SCMODE write command short format can program
the channel open LED threshold by setting V
OTH
[1:0]
(B[13:12]) and change the channel switch mode by set-
ting MC
[1:0] (
B[9:8]). The SCMODE write command long
format can program the channel shorted LED threshold
by setting V
STH
[1:0] (B[11:10]) and change the channel
switch mode by setting MC[1:0] (B[9:8]) and set a new
dimming value by updating DV[7:0] (B[7:0]) in the channel
SCMREG register.
START STOP
SLAVE
ACK
CHANNEL
ADDRESS
SHORT
FORMAT
SLAVE
ACK
1
1 0 1 A
4
A
3
SCMODE DEVICE ADDRESS DATA TO SCMREG
A
2
A
1
0(W)
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9
3965 F08
1 0 0SA SA0
SDA
SCL
0 CA
3
CA
2
CA
1
B[13]B[12] B[9] B[8]
Figure 8. LT3965/LT3965-1 I
2
C Serial Port SCMODE Write Short Format Protocol
