MAX16833 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 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
compensation prevents subharmonic oscillations for
duty cycles exceeding 50% when the inductor is operat-
ing in continuous conduction mode. Most of the power
for the internal control circuitry inside the MAX16833/
MAX16833B 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 floating
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 MAX16833/MAX16833B provide ana-
log 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 MAX16833/MAX16833B 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 resis-
tor in the MAX16833. In the MAX16833B, 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 MAX16833/MAX16833B enter
hiccup mode with automatic recovery from short circuit.
UVLO
The MAX16833/MAX16833B feature undervoltage lock-
out (UVLO) using the positive power-supply input (IN).
The MAX16833/MAX16833B are enabled when VIN
exceeds the 4.6V (typ) threshold and are disabled 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 MAX16833/MAX16833B require an external p-chan-
nel 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 discharging 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 com-
pletely turn on the p-channel dimming MOSFET.
n-Channel MOSFET Switch Driver (NDRV)
The MAX16833/MAX16833B drive an external n-channel
switching MOSFET. NDRV swings between VCC and
PGND. NDRV can sink/source 3A of peak current, allow-
ing the MAX16833/MAX16833B to switch MOSFETs in
high-power applications. The average current demand-
ed from the supply to drive the external MOSFET
depends on the total gate charge (QG) and the operat-
ing 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 MAX16833/MAX16833B 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 discon-
nected 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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