MAX16814ATP+ Maxim Integrated Products, MAX16814ATP+ Datasheet - Page 15

• Manufacturer Part Number: MAX16814ATP+
• Description: LED Drivers Integrated 4-Channel High-Brightness LED
• Manufacturer: Maxim Integrated Products

Specifications of MAX16814ATP+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

flag output (FLT) goes low when an open-LED string is
detected, a shorted LED string is detected, and during
thermal shutdown. FLT is cleared when the fault condi-
tion is removed during thermal shutdown and shorted
LEDs. FLT is latched low for an open-LED condition
and can be reset by cycling power or toggling the EN
pin. The thermal shutdown threshold is +165NC and has
15NC hysteresis.
On power-up, the MAX16814 detects and disconnects
any unused current-sink channels before entering soft-
start. Disable the unused current-sink channels by
connecting the corresponding OUT_ to LEDGND. This
avoids asserting the FLT output for the unused chan-
nels. After soft-start, the MAX16814 detects open LED
and disconnects any strings with an open LED from the
internal minimum OUT_ voltage detector. This keeps the
DC-DC converter output voltage within safe limits and
maintains high efficiency. During normal operation, the
DC-DC converter output regulation loop uses the mini-
mum OUT_ voltage as the feedback input. If any LED
string is open, the voltage at the opened OUT_ goes
to V
increases to the overvoltage protection threshold set by
the voltage-divider network connected between the con-
verter output, OVP input, SGND. The overvoltage protec-
tion threshold at the DC-DC converter output (V
determined using the following formula:
where 1.23V (typ) is the OVP threshold. Select R1 and
R2 such that the voltage at OUT_ does not exceed the
absolute maximum rating. As soon as the DC-DC con-
verter output reaches the overvoltage protection thresh-
old, the PWM controller is switched off setting NDRV
low. Any current-sink output with V
disconnected from the minimum voltage detector.
Connect the OUT_ of all channels without LED connec-
tions to LEDGND before power-up to avoid OVP trigger-
ing at startup. When an open-LED overvoltage condition
occurs, FLT is latched low.
V
Open-LED Management and Overvoltage Protection
OVP
LEDGND
=
1.23
Integrated, 4-Channel, High-Brightness LED
. The DC-DC converter output voltage then
×



1
Driver with High-Voltage DC-DC Controller
+
______________________________________________________________________________________
R2
R1



(see the Typical Operating Circuit)
OUT_
< 300mV (typ) is
OVP
) is
The MAX16814 checks for shorted LEDs at each rising
edge of DIM. An LED short is detected at OUT_ if the
following condition is met:
where V
minimum current-sink voltage, and V
grammable LED short detection threshold set at the
RSDT input. Adjust V
tive network connected at the V
and SGND.
Once a short is detected on any of the strings, the LED
strings with the short are disconnected and the FLT out-
put flag asserts until the device detects that the shorts
are removed on any of the following rising edges of DIM.
Connect RSDT directly to V
short detection.
Three different converter topologies are possible with
the DC-DC controller in the MAX16814, which has the
ground-referenced outputs necessary to use the con-
stant current-sink drivers. If the LED string forward volt-
age is always more than the input supply voltage range,
use the boost converter topology. If the LED string for-
ward voltage falls within the supply voltage range, use
the boost-buck converter topology. Boost-buck topology
is implemented using either a conventional SEPIC con-
figuration or a coupled-inductor boost-buck configura-
tion. The latter is basically a flyback converter with 1:1
turns ratio. 1:1 coupled inductors are available with tight
coupling suitable for this application. Figure 6 shows
the coupled-inductor boost-buck configuration. It is also
possible to implement a single inductor boost-buck con-
verter using the MAX15054 high-side FET driver.
The boost converter topology provides the highest
efficiency among the above mentioned topologies. The
coupled-inductor boost-buck topology has the advan-
tage of not using a coupling capacitor over the SEPIC
configuration. Also, the feedback loop compensation for
SEPIC becomes complex if the coupling capacitor is not
large enough. A coupled-inductor boost-buck is not suit-
able for cases where the coupled-inductor windings are
not tightly coupled. Considerable leakage inductance
requires additional snubber components and degrades
the efficiency.
OUT_
V
OUT_
is the voltage at OUT_, V
Applications Information
> V
RSDT
MINSTR
using a voltage-divider resis-
CC
+ 3 x V
CC
to always disable LED
Short LED Detection
DC-DC Converter
output, RSDT input,
RSDT
RSDT
MINSTR
is the pro-
is the
15