MAX16809 Datasheet, PDF (15/23 Pages) Maxim Integrated Products – Integrated 16-Channel LED Drivers with Switch-Mode Boost and SEPIC Controller

Integrated 16-Channel LED Drivers with
Switch-Mode Boost and SEPIC Controller
The oscillator frequency is then:
f_OSC
=
1
(^tC ⁺
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/MAX16810 include a fast current-limit
comparator to terminate the ON cycle during an over-
load 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 voltage trip level (V_CS) of 0.3V. Use the fol-
lowing 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/MAX16810 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
MAX16810
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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