MAX16809_09 Datasheet, PDF (14/20 Pages) Maxim Integrated Products – Integrated 16-Channel LED Driver with Switch-Mode Boost and SEPIC Controller

Integrated 16-Channel LED Driver with
Switch-Mode Boost and SEPIC Controller
The oscillator frequency is then:
f_OSC
=
(t_C
1
+
t_D)
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:
R_CS
=
V_CS
I_P−P
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.
VIN
L1
C1
D
Q1 L2
COUT
RCS
CC2
CC1
RC1
CIN
3V TO 5.5V
CBYP
EXTERNAL
CLOCK INPUT
EXTERNAL
DIM INPUT
RSET
OUT CS AGND COMP
VCC
FB
V+
OUT0
OUT1
PGND
OUT2
OUT3
MAX16809
OUT4
DIN
OUT5
LE
OUT6
OUT7
CLK
OUT8
DOUT
OUT9
OE
OUT10
OUT11
OUT12
OUT13
OUT14
SET
REF
OUT15
RTCT
RT
CREF
CT
VOUT
R1
R2
Figure 2. Buck-Boost (SEPIC) Operation
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