MAX16809
Integrated 16-Channel LED Driver with
Switch-Mode Boost and SEPIC Controller
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Detailed Description
The MAX16809 LED driver includes an internal switch-
mode controller that can be used as a boost or buck-
boost (SEPIC) converter to generate the voltage
necessary to drive the multiple strings of LEDs. This
device incorporates an integrated low-side driver, a
programmable oscillator (20kHz to 1MHz), an error
amplifier, a low-voltage (300mV) current sense for high-
er efficiency, and a 5V reference to power up external
circuitry (see Figures 1a and 1b).
The MAX16809 LED driver includes a 4-wire serial
interface and a current-mode PWM controller to gener-
ate the necessary voltage for driving 16 open-drain,
constant-current-sinking output ports. The driver uses
current-sensing feedback circuitry (not simple current
mirrors) to ensure very small current variations over the
full allowed range of output voltage (see the
Typical
Operating Characteristics
). The 4-wire serial interface
comprises a 16-bit shift register and a 16-bit transpar-
ent latch. The shift register is written through a clock
input, CLK, and a data input, DIN, and the data propa-
gates to a data output, DOUT. The data output allows
multiple drivers to be cascaded and operated together.
The contents of the 16-bit shift register are loaded into
the transparent latch through a latch-enable input, LE.
The latch is transparent to the shift register outputs
when high and latches the current state on the falling
edge of LE. Each driver output is an open-drain, con-
stant-current sink that should be connected to the
Pin Description
PIN NAME FUNCTION
1, 31, 32,
36, 38
N.C. No Connection. Not internally connected. Leave unconnected.
2 FB Error-Amplifier Inverting Input
3 COMP Error-Amplifier Output
4–11 OUT8–OUT15 LED Driver Outputs. OUT8–OUT15 are open-drain, constant-current-sinking outputs rated for 36V.
12 OE
Active-Low, Output Enable Input. Drive OE low to PGND to enable the OUT0–OUT15. Drive OE
high to disable OUT0–OUT15.
13 DOUT
Serial-Data Output. Data is clocked out of the 16-bit internal shift register to DOUT on CLK’s
rising edge.
14 SET LED Current Setting. Connect R
SET
from SET to PGND to set the LED current.
15 V+ LED Driver Positive Supply Voltage. Bypass V+ to PGND with a 0.1μF ceramic capacitor.
16, 17 PGND Power Ground
18 DIN Serial-Data Input. Data is loaded into the internal 16-bit shift register on CLK’s rising edge.
19 CLK Serial-Clock Input
20 LE
Latch-Enable Input. Data is loaded transparently from the internal shift register(s) to the output
latch(es) while LE is high. Data is latched into the output latch(es) on LE’s falling edge, and
retained while LE is low.
21–28 OUT0–OUT7 LED Driver Outputs. OUT0–OUT7 are open-drain, constant-current-sinking outputs rated for 36V.
29 RTCT
PWM Controller Timing Resistor/Capacitor Connection. A resistor R
T
from RTCT to REF and a
capacitor C
T
from RTCT to AGND set the oscillator frequency.
30 CS PWM Controller Current-Sense Input
33 AGND Analog Ground
34 OUT MOSFET Driver Output OUT. Connects to the gate of the external n-channel MOSFET.
35 V
CC
Power-Supply Input. Bypass V
CC
to AGND with a 0.1μF ceramic capacitor or a parallel
combination of a 0.1μF and a higher value ceramic capacitor.
37 REF 5V Reference Output. Bypass REF to AGND with a 0.1μF ceramic capacitor.
—EP
Exposed Paddle. Connect to the ground plane for improved power dissipation. Do not use as the
only ground connection.
