MAX16833_11 Datasheet, PDF (11/22 Pages) Maxim Integrated Products – High-Voltage HB LED Drivers with Integrated High-Side Current Sense

High-Voltage HB LED Drivers with
Integrated High-Side Current Sense
Detailed Description
The MAX16833/MAX16833B/MAX16833C/MAX16833D/
MAX16833E are peak current-mode-controlled LED
drivers for boost, buck-boost, SEPIC, flyback, and high-
side buck topologies. A low-side gate driver capable
of sinking and sourcing 3A can drive a power MOSFET
in the 100kHz to 1MHz frequency range. Constant-
frequency peak current-mode control is used to control
the duty cycle of the PWM controller that drives the
power MOSFET. Externally programmable slope com-
pensation prevents subharmonic oscillations for duty
cycles exceeding 50% when the inductor is operating
in continuous conduction mode. Most of the power for
the internal control circuitry inside the ICs is provided
from an internal 5V regulator. The gate drive for the low-
side switching MOSFET is provided by a separate VCC
regulator. A dimming driver designed to drive an external
p-channel in series with the LED string provides wide-
range dimming control. This dimming driver is powered
by a separate unconnected reference -7V regulator. This
feature provides extremely fast PWM current switching to
the LEDs with no transient overvoltage or undervoltage
conditions. In addition to PWM dimming, the ICs provide
analog dimming using a DC input at the ICTRL input.
A single resistor from RT/SYNC to ground sets the
switching frequency from 100kHz to 1MHz, while an
external clock signal capacitively coupled to RT/SYNC
allows the ICs to synchronize to an external clock. The
switching frequency can be dithered for spread-spectrum
applications by connecting the LFRAMP output to RT/SYNC
through an external resistor in the MAX16833/MAX16833C/
MAX16833E. In the MAX16833B/MAX16833D, the LFRAMP
output is replaced by a REF output, which provides a
regulated 1.64V, 2% accurate reference that can be
used with a resistive divider from REF to ICTRL to set the
LED current. The maximum current from the REF output
cannot exceed 80FA.
Additional features include a fault-indicator output (FLT)
for short, overvoltage, or overtemperature conditions
and an overvoltage-protection (OVP) sense input for
overvoltage protection. In case of LED string short, for
a buck-boost configuration, the short-circuit current is
equal to the programmed LED current. In the case of
boost configuration, the ICs enter hiccup mode with
automatic recovery from short circuit.
UVLO
The ICs feature undervoltage lockout (UVLO) using the
positive power-supply input (IN). The ICs are enabled
when VIN exceeds the 4.6V (typ) threshold and are dis-
abled when VIN drops below the 4.35V (typ) threshold.
The UVLO is internally fixed and cannot be adjusted.
There is a startup delay of 1024 clock cycles on power-
up after the UVLO threshold is crossed. There is a 3.3Fs
delay on power-down on the falling edge of the UVLO.
Dimming MOSFET Driver (DIMOUT)
The ICs require an external p-channel MOSFET for PWM
dimming. For normal operation, connect the gate of the
MOSFET to the output of the dimming driver (DIMOUT).
The dimming driver can sink up to 25mA or source up
to 50mA of peak current for fast charging and discharg-
ing of the p-MOSFET gate. When the PWMDIM signal is
high, this driver pulls the p-MOSFET gate to 7V below
the ISENSE+ pin to completely turn on the p-channel
dimming MOSFET.
n-Channel MOSFET Switch Driver (NDRV)
The ICs drive an external n-channel switching MOSFET.
NDRV swings between VCC and PGND. NDRV can sink/
source 3A of peak current, allowing the ICs to switch
MOSFETs in high-power applications. The average cur-
rent demanded from the supply to drive the external
MOSFET depends on the total gate charge (QG) and
the operating frequency of the converter, fSW. Use the
following equation to calculate the driver supply current
INDRV required for the switching MOSFET:
INDRV = QG x fSW
Pulse-Dimming Input (PWMDIM)
The ICs offer a dimming input (PWMDIM) for pulse-width
modulating the output current. PWM dimming can be
achieved by driving PWMDIM with a pulsating voltage
source. When the voltage at PWMDIM is greater than
1.23V, the PWM dimming p-channel MOSFET turns on
and the gate drive to the n-channel switching MOSFET is
also enabled. When the voltage on PWMDIM drops 70mV
below 1.23V, the PWM dimming MOSFET turns off and
the n-channel switching MOSFET is also turned off. The
COMP capacitor is also disconnected from the internal
transconductance amplifier when PWMDIM is low. When
left unconnected, a weak internal pullup resistor sets this
input to logic-high.
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