MAX16807_09 Datasheet, PDF (15/19 Pages) Maxim Integrated Products – Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller

Integrated 8-Channel LED Driver with
Switch-Mode Boost and SEPIC Controller
LED Driver
4-Wire Interface
The MAX16807 also operates in a stand-alone mode
(see the Typical Operating Circuits). For use with a
microcontroller, the MAX16807 features a 4-wire serial
interface using DIN, CLK, LE, OE inputs and DOUT as
a data output. This interface is used to write the LED
channels’ data to the MAX16807. The serial-interface
data word length is 8 bits, D0–D7. See Figure 3.
The functions of the five interface pins are as follows:
DIN is the serial-data input, and must be stable when it
is sampled on the rising edge of CLK. Data is shifted in
MSB first. This means that data bit D7 is clocked in first,
followed by 7 more data bits, finishing with the LSB, D0.
CLK is the serial-clock input that shifts data at DIN into
the MAX16807’s 8-bit shift register on its rising edge.
LE is the latch enable input of the MAX16807 that trans-
fers data from the 8-bit shift register to its 8-bit output
latch (transparent latch). The data is latched on the
falling edge of LE (Figure 4). The fourth input (OE) pro-
vides output-enable control of the output drivers. When
OE is driven high, the outputs (OUT0–OUT7) are forced
to high impedance without altering the contents of the
output latches. Driving OE low enables the outputs to
follow the state of the output latches. OE is indepen-
dent of the operation of the serial interface operation.
Data can be shifted into the serial-interface shift regis-
ter and latched, regardless of the state of OE. DOUT is
the serial-data output that shifts data out from the
MAX16807’s 8-bit shift register on the rising edge of
CLK. Data at DIN propagates through the shift register
and appears at DOUT eight clock cycles later. Table 1
shows the 4-wire serial-interface truth table.
Selecting External Component
R_SET to Set LED Output Current
The MAX16807 uses an external resistor, R_SET, to set
the LED current for outputs OUT0–OUT7. The minimum
allowed value of R_SET is 330Ω, which sets the output
currents to 55mA. The maximum allowed value of R_SET
is 5kΩ (I_{OUT_} = 3.6mA) and maximum allowed capaci-
tance at SET is 100pF.
Use the following formula to set the output current:
R_SET
=
18,000
I_OUT _
where I_{OUT_} is the desired output current in milliamps
and the value for R_SET is in ohms.
Overtemperature Cutoff
The MAX16807 contains an internal temperature sensor
that turns off all outputs when the die temperature
exceeds +165°C. The outputs are enabled again when
the die temperature drops below +140°C. Register con-
tents are not affected, so when a driver is overdissipat-
ing, the external symptom is the load LEDs cycling on
and off as the driver repeatedly overheats and cools,
alternately turning itself off and then back on again.
Table 1. 4-Wire Serial-Interface Truth Table
SERIAL
DATA
CLOCK
INPUT
SHIFT REGISTER
CONTENTS
LOAD
INPUT
INPUT
DIN ^{CLK D0 D1 D2 … Dn-1 Dn LE}
LATCH CONTENTS
D0 D1 D2 … Dn-1 Dn
BLANKING
INPUT
OE
OUTPUT CONTENTS
CURRENT AT OUT_
D0 D1 D2 … Dn-1 Dn
H
H R0 R1 … Rn-2 Rn-1
L
L R0 R1 … Rn-2 Rn-1
X
R0 R1 R2 … Rn-1 Rn
X X X… X X
L R0 R1 R2 … Rn-1 Rn
P0 P1 P2 … Pn-1 Pn
H P0 P1 P2 … Pn-1 Pn
L
P0 P1 P2 … Pn-1 Pn
X X X… X X
H
L L L… L L
L = Low Logic Level
H = High Logic Level
X = Don’t Care
P = Present State (Shift Register)
R = Previous State (Latched)
______________________________________________________________________________________ 15