Datasheet

The oscillator frequency is then:
( )
OSC
CD
1
f
t t
=
+
Reference Output
REF is a 5V reference output that can source 20mA.
Bypass REF to AGND with a 0.1µF capacitor.
Current Limit
The MAX16809 includes a fast current-limit comparator
to terminate the ON cycle during an overload or a fault
condition. The current-sense resistor, R
CS
, connected
between the source of the external MOSFET and
AGND, sets the current limit. The CS input has a volt-
age trip level (V
CS
) of 0.3V. Use the following equation
to calculate R
CS
:
CS
CS
PP
V
R
I
−
=
I
P-P
is the peak current that flows through the MOSFET.
When the voltage produced by this current (through the
current-sense resistor) exceeds the current-limit com-
parator threshold, the MOSFET driver (OUT) turns the
switch off within 60ns. In most cases, a small RC filter is
required to filter out the leading-edge spike on the sense
waveform. Set the time constant of the RC filter at 50ns.
Buck-Boost (SEPIC) Operation
Figure 2 shows a buck-boost application circuit using
the MAX16809 in a stand-alone mode of operation.
SEPIC topology is necessary when the total forward
voltage of the LEDs in a string is such that V
OUT
can be
below or above V
IN
.
Figure 2. Buck-Boost (SEPIC) Operation
MAX16809
OUT0
FB
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
OUT7
OUT8
OUT9
OUT10
OUT11
OUT12
OUT13
OUT14
OUT15
EXTERNAL
DIM INPUT
EXTERNAL
CLOCK INPUT
SET
LE
DIN
PGND
V
CC
V+
OE
DOUT
CLK
REF
RTCT
C
REF
C
IN
R
SET
R
CS
C
1
C
C2
C
C1
OUT CS AGND COMP
R
C1
R2
R1
C
OUT
C
BYP
R
T
C
T
3V TO 5.5V
V
IN
V
OUT
Q1
D
L1
L2
www.maximintegrated.com
Maxim Integrated │ 14
MAX16809 Integrated 16-Channel LED Driver with
Switch-Mode Boost and SEPIC Controller