MAX16838B Datasheet, PDF (12/21 Pages) Maxim Integrated Products – Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller

MAX16838B
Integrated, 2-Channel, High-Brightness LED Driver
with High-Voltage Boost and SEPIC Controller
Detailed Description
The MAX16838B 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 pro-
tection up to 40V in automotive applications. The device
incorporates a DC-DC controller with peak current-mode
control to implement a boost, coupled-inductor boost-
buck, or SEPIC-type switched-mode power supply and
a 2-channel LED driver with 20mA to 150mA constant-
current-sink capability per channel. The MAX16838B can
be combined with the MAX15054 to achieve boost-buck
topology without a coupled inductor (see Figure 5).
The device features a constant-frequency peak current-
mode control with internal slope compensation to control
the duty cycle of the PWM controller. The DC-DC con-
verter 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 2-chan-
nel constant current sinks that control the current through
the LED strings. A single resistor connected from ISET to
ground sets the forward current through both LED strings.
The device features adaptive LED voltage control that
adjusts the converter output voltage depending on the
forward voltage of the LED strings. This feature minimiz-
es the voltage drops across the constant-current sinks
and reduces power dissipation in the device. The device
provides a very wide PWM dimming range where a
dimming pulse as narrow as 500ns is possible at a 200Hz
dimming frequency.
A logic input (EN) shuts down the device when pulled low.
The device includes an internal 5V LDO to power up the
internal circuitry and drive the internal switching MOSFET.
The device includes output overvoltage protection that
limits the converter output voltage to the programmed
OV threshold in the event of an open-LED condition. The
device also features an overtemperature protection that
shuts down the controller if the die temperature exceeds
+165°C. In addition, the MAX16838B has a shorted-LED
string detection and an open-drain FLT signal to indicate
open-LED, shorted-LED, and overtemperature conditions.
Features
Additional features of the MAX16838B include:
●● Integrated, 2-Channel, 20mA to 150mA Linear LED
Current Sinks
●● Boost or SEPIC Power Topologies for Maximum
Flexibility
●● Adaptive Voltage Optimization to Minimize Power
Dissipation in Linear Current Sinks
●● 4.75V to 40V or 5V ±10% Input Operating Voltage
Range
●● 10,000:1 PWM Dimming at 200Hz
●● Open-Drain Fault-Indicator Output
●● LED Open/Short Detection and Protection
●● Output Overvoltage and Overtemperature Protection
●● Programmable LED Current Foldback at Lower Input
Voltages
●● 200kHz to 2MHz Resistor-Programmable Switching
Frequency with External Synchronization
●● Current-Mode Control Switching Stage with Internal
Slope Compensation
●● Enable Input
●● Thermally Enhanced 20-Pin TSSOP (4.4mm) and
TQFN (4mm x 4mm) Packages
Current-Mode DC-DC Controller
The device uses current-mode control to provide the
required supply voltage for the LED strings. The internal
MOSFET is turned on at the beginning of every switch-
ing 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 sensedfrom the voltage
across the current-sense resistor (R_CS) connected from
the source of the internal MOSFET to PGND. A PWM
comparator compares the current-sense voltage plus the
internal slope-compensation signal with the output of the
transconductance error amplifier. The controller turns off
the internal 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 feedback
(FB) signal with an internal reference voltage (V_REF) and
regulates its output to adjust the inductor current. An
internal minimum string detector measures the minimum
LED string cathode voltage with respect to SGND. During
normal operation, this minimum V_{OUT_} voltage is regulated
to 1V through feedback. The resulting DC-DC converter
output voltage is 1V above the maximum required total
LED voltage.
The converter stops switching when LED strings are
turned off during PWM dimming. The error amplifier
is disconnected from the COMP output to retain the
compensation capacitor charge. This allows the
converter to settle to a steady-state level immediately
when the LED strings are turned on again. This unique
feature provides fast dimming response without having to
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