MAX16807AUI datasheet(15/21 Pages) MAXIM

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Integrated 8-Channel LED Drivers with

Switch-Mode Boost and SEPIC Controller

______________________________________________________________________________________

where tD is in seconds, RT in ohms (Ω), and CT in

Farads (F).

The oscillator frequency is then:

Reference Output

REF is a 5V reference output that can source 20mA.

Bypass REF to AGND with a 0.1µF capacitor.

Current Limit

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,

RCS, connected between the source of the external

MOSFET and AGND, sets the current limit. The CS

input has a voltage trip level (VCS) of 0.3V. Use the fol-

lowing equation to calculate RCS:

IP-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 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

VOUT can be below or above VIN.

−

OSC

()

MAX16807

MAX16808

OUT0

OUT1

OUT2

OUT3

OUT4

OUT5

OUT6

OUT7

EXTERNAL

DIM INPUT

EXTERNAL

CLOCK INPUT

SET

DIN

PGND

VCC

V+

DOUT

CLK

REF

RTCT

CREF

CBYP

RSET

RCS

CC2

CC1

OUT CS AGND

COMP

RC1

C N

3V TO 5 5V

V N

VOUT

LEDs

COUT

Figure 2. Buck-Boost (SEPIC) Configuration

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