Detailed description, Pin description (continued) – Rainbow Electronics MAX16831 User Manual

Page 9

MAX16831

High-Voltage, High-Power LED Driver with

Analog and PWM Dimming Control

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Detailed Description

The MAX16831 is a current-mode PWM LED driver
used for driving HBLEDs. By using two current regula-
tion loops, 5% output current accuracy is achieved.
One current regulation loop controls the external
switching MOSFET peak current through a sense resis-
tor, R

SENSE

, from SNS+ to SNS-, while the other current

regulation loop controls the average LED string current
through the sense resistor R

in series with the LEDs.

The wide operating supply range of (6.0V/5.5V
ON/OFF) up to 76V makes the MAX16831 ideal in auto-
motive applications.

The MAX16831 features a programmable undervoltage
lockout (UVEN) that ensures predictable operation dur-
ing brownout conditions. The input UVEN circuit moni-
tors the supply voltage, V

, and turns the driver off

when V

drops below the UVLO threshold. Connect

UVEN to V

to use the 5.7V (typ) default UVLO thresh-

old. The MAX16831 includes a cycle-by-cycle current
limit that turns off the gate drive to the external switch-
ing MOSFET (Q

) during an overcurrent condition. The

MAX16831 features a programmable oscillator that sim-
plifies and optimizes the design of external magnetics.

The MAX16831 includes three internal voltage regula-
tors, REG1, REG2, and CLMP, and a 3V buffered refer-
ence output, REF. Connect REG2 to the driver supply,
DRI, to power the switching MOSFET driver.

The MAX16831 is capable of synchronizing with an
external clock or operating in stand-alone mode. A sin-
gle resistor, R

, can be used to adjust the switching fre-

quency from 125kHz to 600kHz for stand-alone
operation. To synchronize the device with an external
clock, apply a clock signal directly to the RTSYNC
input. A buffered clock output, CLKOUT, is available to
configure the MAX16831 in multichannel applications.

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Pin Description (continued)

PIN

NAME

FUNCTION

QGND

Analog Ground. Ensure a low-impedance connection between QGND and AGND.

DGT

Dimming Gate Driver Output. Connect DGT to the gate of an external n-channel MOSFET for
dimming. DGT is powered by the internal regulator, CLMP, and is referenced to LO.

Low-Voltage Input. LO is the return point for the LED current. When using the MAX16831 in a buck-
boost configuration, connect LO to V

. When using the device in a boost configuration only,

connect LO to SGND. Connect LO to the junction of the inductor and LED current-sense resistor,
R

, when using a buck configuration.

CS+

Noninverting Current-Sense Amplifier Input. Connect CS+ to the positive side of an external sense
resistor, R

, connected in series with the load (LEDs).

CS-

Inverting Current-Sense Amplifier Input. Connect CS- to the negative side of an external sense
resistor, R

, connected in series with the load (LEDs).

CLMP

Internal CLMP Regulator Output. CLMP supplies an 8V (typ) output when V

≥ 9V. If V

is lower than

9V, V

CLMP

is one diode drop below V

. The CLMP regulator powers the current-sense amplifier and

provides the high reference for the dimming driver. V

CLMP

must be at least 2.5V higher than V

enable the current-sense amplifier and dimming MOSFET driver. Bypass CLMP to LO with a 0.1µF
ceramic capacitor.

High-Voltage Input. HI is referred to LO. HI supplies power to the current-sense amplifier and
dimming MOSFET gate driver through the CLMP regulator.

REG2

Internal Regulator Output. REG2 is an internal voltage regulator that generates a 7V output and
supplies power to internal circuitry. Connect REG2 to DRI to power the switching MOSFET driver
during normal operation. Bypass REG2 to AGND with a 10µF ceramic capacitor.

Supply Voltage Input

I.C.

Internally Connected. Must be connected directly to QGND.

—

Exposed Pad. Connect EP to AGND. EP also functions as a heatsink to maximize thermal dissipation.
Do not use as a ground connection.