MAX16808 Maxim Integrated Products, MAX16808 Datasheet - Page 11

• Manufacturer Part Number: MAX16808
• Description: (MAX16807 / MAX16808) Integrated 8-Channel LED Drivers
• Manufacturer: Maxim Integrated Products

The MAX16807/MAX16808 LED drivers include an
internal switch-mode controller that can be used as
boost or buck-boost (SEPIC) converters to generate the
voltage necessary to drive the multiple strings of LEDs.
These devices incorporate an integrated low-side dri-
ver, a programmable oscillator (20kHz to 1MHz), an
error amplifier, a low-voltage (300mV) current sense for
higher efficiency, and a 5V reference to power up
external circuitry (see Figures 1a, 1b, and 1c).
The MAX16807/MAX16808 LED drivers include a 4-wire
serial interface and a current-mode PWM controller to
generate the necessary voltage for driving eight open-
drain, constant-current-sinking output ports. The drivers
1, 13, 28
15, 16
20–23
PIN
6–9
10
11
12
14
17
18
19
24
25
26
27
—
2
3
4
5
OUT4–OUT7
OUT0–OUT3
Switch-Mode Boost and SEPIC Controller
NAME
AGND
COMP
DOUT
PGND
RTCT
OUT
N.C.
CLK
______________________________________________________________________________________
V
REF
SET
DIN
OE
V+
CS
LE
FB
EP
CC
Detailed Description
Integrated 8-Channel LED Drivers with
No Connection. Not internally connected. Leave unconnected.
Analog Ground
MOSFET Driver Output OUT. Connects to the gate of the external n-channel MOSFET.
Power-Supply Input. Bypass V
of a 0.1µF and a higher value ceramic capacitor.
5V Reference Output. Bypass REF to AGND with a 0.1µF ceramic capacitor.
LED Driver Outputs. OUT4–OUT7 are open-drain, constant-current-sinking outputs rated for 36V.
Active-Low Output Enable Input. Drive OE low to PGND to enable the OUT0–OUT7. Drive OE high to
disable OUT0–OUT7.
Serial-Data Output. Data is clocked out of the 8-bit internal shift register to DOUT on CLK’s rising
edge.
LED Current Setting. Connect R
LED Driver Positive Supply Voltage. Bypass V+ to PGND with a 0.1µF ceramic capacitor.
Power Ground
Serial-Data Input
Serial-Clock Input
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.
LED Driver Outputs. OUT0–OUT3 are open-drain, constant-current-sinking outputs rated for 36V.
Error-Amplifier Output
Error-Amplifier Inverting Input
PWM Controller Current-Sense Input
PWM Controller Timing Resistor/Capacitor Connection. A resistor R
capacitor C
Exposed Paddle. Connect to the ground plane for improved power dissipation. Do not use as the
only ground connection for the part.
T
from RTCT to AGND set the oscillator frequency.
CC
SET
to AGND with a 0.1µF ceramic capacitor or a parallel combination
from SET to PGND to set the LED current.
use current-sensing feedback circuitry (not simple cur-
rent 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 an 8-bit shift register and an 8-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 8-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 cath-
FUNCTION
T
from RTCT to REF and a
Pin Description
11