MAX16814_15 Datasheet, PDF (12/25 Pages) Maxim Integrated Products – Integrated, 4-Channel, High-Brightness LED Driver with High-Voltage DC-DC Controller

MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Detailed Description
The MAX16814 high-efficiency HB LED driver
integrates all the necessary features to implement a
high-performance backlight driver to power LEDs in
small to medium-sized displays for automotive as well
as general applications. The device provides load-dump
voltage protection up to 40V in automotive applications.
The MAX16814 incorporates two major blocks: a DC-DC
controller with peak current-mode control to implement
a boost, coupled-inductor boost-buck, or a SEPIC-type
switched-mode power supply and a 4-channel LED
driver with 20mA to 150mA constant current-sink capa-
bility per channel. Figure 1 is the simplified functional
diagram and Figure 2 shows the circuit used for typical
operating characteristics.
The MAX16814 features a constant-frequency peak
current-mode control with programmable slope
compensation to control the duty cycle of the PWM
controller. The high-current FET driver can provide up
to 2A of current to the external n-channel MOSFET.
The DC-DC converter implemented using the controller
generates the required supply voltage for the LED
strings from a wide input supply range. Connect LED
strings from the DC-DC converter output to the 4-channel
constant current-sink drivers that control the current
through the LED strings. A single resistor connected
from the SETI input to ground adjusts the forward current
through all four LED strings.
The MAX16814 features adaptive voltage control that
adjusts the converter output voltage depending on the
forward voltage of the LED strings. This feature mini-
mizes the voltage drop across the constant current-sink
drivers and reduces power dissipation in the device.
A logic input (EN) shuts down the device when pulled
low. The device includes an internal 5V LDO capable of
powering additional external circuitry.
All the versions of the MAX16814 include PWM dimming.
The MAX16814A_ and the MAX16814U_ versions, in par-
ticular, provide very wide (5000:1) PWM dimming range
where a dimming pulse as narrow as 1µs is possible at
a 200Hz dimming frequency. This is made possible by
a unique feature that detects short PWM dimming input
pulses and adjusts the converter feedback accordingly.
Advanced features include detection and string-
disconnect for open-LED strings, partial or fully shorted
strings, and unused strings. Overvoltage protection
clamps the converter output voltage to the programmed
OVP threshold in the event of an open-LED condi-
tion. Shorted LED string detection and overvoltage
protection thresholds are programmable using RSDT
and OVP inputs, respectively. An open-drain FLT signal
asserts to indicate open-LED, shorted-LED, and over-
temperature conditions. Disable individual current-sink
channels by connecting the corresponding OUT_ to
LEDGND. In this case, FLT does not assert indicating
an open-LED condition for the disabled channel. The
device also features an overtemperature protection that
shuts down the controller if the die temperature exceeds
+165NC.
Current-Mode DC-DC Controller
The peak current-mode controller allows boost, coupled-
inductor buck-boost, or SEPIC-type converters to gener-
ate the required bias voltage for the LED strings. The
switching frequency can be programmed over the 200kHz
to 2MHz range using a resistor connected from RT to
SGND. Programmable slope compensation is available
to compensate for subharmonic oscillations that occur at
above 50% duty cycles in continuous-conduction mode.
The external MOSFET is turned on at the beginning of
every switching cycle. The inductor current ramps up
linearly until it is turned off at the peak current level set by
the feedback loop. The peak inductor current is sensed
from the voltage across the current-sense resistor (RCS)
connected from the source of the external MOSFET to
PGND. The MAX16814 features leading-edge blanking to
suppress the external MOSFET switching noise. A PWM
comparator compares the current-sense voltage plus the
slope-compensation signal with the output of the transcon-
ductance error amplifier. The controller turns off the exter-
nal MOSFET when the voltage at CS exceeds the error
amplifier’s output voltage. This process repeats every
switching cycle to achieve peak current-mode control.
Error Amplifier
The internal error amplifier compares an internal feed-
back (FB) with an internal reference (REF) and regulates
its output to adjust the inductor current. An internal mini-
mum string detector measures the minimum current-sink
voltage with respect to SGND out of the four constant-
current-sink channels. During normal operation, this
minimum OUT_ voltage is regulated to 1V through
feedback. The error amplifier takes 1V as the REF
and the minimum OUT_ voltage as the FB input. The
amplified error at the COMP output controls the inductor
peak current to regulate the minimum OUT_ voltage at
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