MAX16808 Maxim Integrated Products, MAX16808 Datasheet - Page 15

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

where t
Farads (F).
The oscillator frequency is then:
REF is a 5V reference output that can source 20mA.
Bypass REF to AGND with a 0.1µF capacitor.
The MAX16807/MAX16808 include a fast current-limit
comparator to terminate the on cycle during an over-
load or a fault condition. The current-sense resistor,
R
MOSFET and AGND, sets the current limit. The CS
input has a voltage trip level (V
lowing equation to calculate R
Figure 2. Buck-Boost (SEPIC) Configuration
CS
, connected between the source of the external
D
is in seconds, R
3V TO 5.5V
Switch-Mode Boost and SEPIC Controller
CLOCK INPUT
______________________________________________________________________________________
f
OSC
EXTERNAL
DIM INPUT
R
EXTERNAL
V
SET
IN
C
BYP
C
IN
Integrated 8-Channel LED Drivers with
=
(
t
T
C
CS
V
V+
PGND
DIN
LE
CLK
DOUT
OE
SET
in ohms (Ω), and C
OUT CS AGND
CC
+
1
CS
L1
C
:
REF
Reference Output
t
) of 0.3V. Use the fol-
D
REF
)
Current Limit
MAX16807
MAX16808
Q
R
R
CS
T
COMP
C1
C
L2
T
C
RTCT
C1
C
C2
D
OUT0
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
OUT7
T
R
C
C1
FB
OUT
in
I
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.
Figure 2 shows a buck-boost application circuit using
the MAX16807/MAX16808 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
R1
R2
P-P
OUT
V
OUT
is the peak current that flows through the MOSFET.
can be below or above V
Buck-Boost (SEPIC) Operation
R
CS
=
I
V
P P
CS
−
IN
.
LEDs
15