MAX16831ATJ/V+ Datasheet MAX16831ATJ+, MAX16831ATJ+T, MAX16831ATJ/V+ | P10-P12

MAX16831

High-Voltage, High-Power LED Driver with

Analog and PWM Dimming Control

Maxim Integrated

The MAX16831 features a differential high-side level

shifter to drive an external n-channel MOSFET for dim-

ming. Wide contrast “pulsed” dimming (1000:1) is pos-

sible by applying either a low-frequency PWM input

signal or a DC voltage to the dimming input (DIM).

Protection features include peak current limiting,

HICCUP mode current limiting, output overvoltage pro-

tection, short-circuit protection, and thermal shutdown.

The HICCUP current-limit circuitry reduces the power

delivered to the load during severe fault conditions.

Nonlatching overvoltage protection limits the voltage on

the external switching MOSFET (Q

) under open-circuit

conditions in the LED string. During continuous opera-

tion at high input voltages, the power dissipation of the

MAX16831 could exceed the maximum rating and an

internal thermal shutdown circuitry safely turns off the

MAX16831 when the device junction temperature

exceeds +165°C. When the junction temperature drops

below the hysteresis temperature, the MAX16831 auto-

matically re-initiates startup.

Undervoltage Lockout/Enable

The MAX16831 features a dual-purpose adjustable

UVLO input and enable function. Connect UVEN to V

through a resistive voltage-divider to set the undervolt-

age lockout (UVLO) threshold. The MAX16831 is

enabled when the UVEN exceeds the 1.244V (typ)

threshold. Drive UVEN to ground to disable the output.

Setting the UVLO Threshold

The MAX16831 features a programmable UVLO thresh-

old. Connect UVEN directly to V

to select the default

6.0V (max) UVLO threshold. Connect UVEN to V

through a resistive voltage-divider to select a UVLO

threshold (Figure 1). Calculate resistor values as follows:

where R

UV1

+ R

UV2

≤ 270kΩ, V

UVEN

is the 1.244V (typ)

threshold voltage, and V

UVLO

is the desired UVLO

threshold in volts at V

(Figure 1).

The capacitor, C

UVEN

, is required to prevent chattering

at the UVLO threshold due to line impedance drops

during power-up and dimming. If the undervoltage set-

ting is very close to the required minimum operating

voltage, then there can be jumps in the voltage at V

during dimming, which may cause the MAX16831 to

turn on and off when the dimming signal transitions

from low to high. The capacitor, C

UVEN

, should be

large enough to limit the ripple on UVEN to less than

the 100mV (min) UVEN hysteresis so that the device

does not turn off under these circumstances.

Soft-Start

The MAX16831 includes a factory-set 4ms (typ) soft-

start delay that allows the load current to ramp up in a

controlled manner, minimizing output overshoot. Soft-

start begins once the device is enabled and V

exceeds the UVLO threshold. Soft-start circuitry slowly

increases the internal soft-start voltage, V

, resulting

in a controlled rise of the load current. Signals applied

to DIM are ignored until the soft-start duration is com-

plete and a successive delay of 200µs has elapsed.

Internal Regulators

The MAX16831 includes a fixed 5V voltage regulator

REG1, a 7V voltage regulator REG2, and an internal 8V

regulator CLMP. REG1 and REG2 power up when V

exceeds the UVLO threshold. REG1 supplies power to

internal circuitry and remains on during PWM dimming.

It is capable of driving external loads up to 2mA.

REG2 is capable of delivering up to 20mA of current.

Connect REG2 to DRI to generate the supply voltage

for the primary switching MOSFET driver, DRV.

CLMP is powered by HI and supplies power to the cur-

rent-sense amplifier (CSA). CSA is enabled when

CLMP

goes 2.5V above V

and is disabled when

CLMP

- V

) falls below 2.28V. The CLMP regulator

also provides power to the dimming MOSFET control

circuitry. CLMP is the output of the CLMP regulator. Do

not use CLMP to power external circuitry. Bypass

CLMP to LO with a 0.1µF ceramic capacitor. A larger

capacitor will result in overshoots of the load current.

UV UV

UVEN

UVLO UVEN

=×

⎛

⎝

⎜

⎞

⎠

⎟

MAX16831

UVEN

QGND

UV2

UV1

UVEN

Figure 1. Setting the UVLO Threshold

MAX16831

High-Voltage, High-Power LED Driver with

Analog and PWM Dimming Control

Maxim Integrated

Reference Voltage Output

The MAX16831 includes a 5% accurate 3V (typ)

buffered reference output, REF. REF is a push-pull out-

put capable of sourcing/sinking 100µA of current and

can drive a maximum load capacitance of 100pF.

Connect REF to DIM through a resistive voltage-divider

to supply an analog signal for dimming. See the

Dimming Input (DIM)

section.

Dimming MOSFET Driver (DDR)

The MAX16831 requires an external n-channel

MOSFET for PWM dimming. Connect the MOSFET to

the output of the DDR dimming driver, DGT, for normal

operation. V

DGT

swings between V

and V

CLMP

. The

DDR dimming driver is capable of sinking or sourcing

up to 20mA of current. The average current required to

drive the dimming MOSFET (I

DRIVE_DIM

) depends on

the MOSFET’s total gate charge (Q

G_DIM

) and the dim-

ming frequency of the converter, f

DIM

. Use the follow-

ing equation to calculate the average gate drive current

for the n-channel dimming FET.

DRIVE_DIM

= Q

G_DIM

x f

DIM

n-Channel MOSFET Switch Driver (DRV)

The MAX16831 drives an external n-channel MOSFET.

Use an external supply or connect REG2 to DRI to

power the MOSFET driver. The driver output, V

DRV

swings between ground and V

DRI

. Ensure that V

DRI

remains below the absolute maximum V

rating of the

external MOSFET. DRV is capable of sinking 2.5A or

sourcing 1.4A of peak current, allowing the MAX16831

to switch MOSFETs in high-power applications. The

average current sourced to drive the external MOSFET

depends on the total gate charge (Q

) and operating

frequency of the converter, f

. The power dissipation

in the MAX16831 is a function of the average output

drive current (I

DRIVE

). Use the following equations to

calculate the power dissipation in the gate driver sec-

tion of the MAX16831 due to I

DRIVE

= Q

x f

= (I

DRIVE

+ I

) x V

DRI

where V

DRI

is the supply voltage to the gate driver and

is the operating supply current. I

DRIVE

should not

exceed 20mA.

Dimming Input (DIM)

The dimming input, DIM, functions with either analog or

PWM control signals. Once the internal pulse detector

detects three successive edges of a PWM signal with a

frequency between 80Hz and 2kHz, the MAX16831 syn-

chronizes to the external signal and pulse-width-modu-

lates the LED current at the external DIM input frequency

with the same duty cycle as the DIM input. If an analog

control signal is applied to DIM, the MAX16831 com-

pares the DC input to an internally generated 200Hz

ramp to pulse-width-modulate the LED current (f

DIM

200Hz). The output current duty cycle is linearly

adjustable from 0 to 100% (0.2V < V

DIM

< 2.8V).

Use the following formula to calculate the voltage, V

DIM

necessary for a given output-current duty cycle, D:

DIM

= (D x 2.6) + 0.2V

where V

DIM

is the voltage applied to DIM in volts.

Connect DIM to REF through a resistive voltage-divider

to apply a DC DIM control signal (Figure 2). Use the

required dimming input voltage, V

DIM

, calculated

above and select appropriate resistor values using the

following equation:

= R

x V

DIM

/ (V

REF

- V

DIM

)

where V

REF

is the 3V reference output voltage and

30kΩ≤R

+ R

≤ 150kΩ.

For proper operation at startup or after toggling ENABLE,

the controller needs three clock edges or an analog volt-

age greater than 0.3V on the DIM input.

Oscillator, Clock, and Synchronization

The MAX16831 is capable of stand-alone operation or

synchronizing to an external clock, and driving external

devices in SYNC mode. For stand-alone operation, pro-

gram the switching frequency by connecting a single

external resistor, R

, between RTSYNC and ground.

Select the switching frequency, f

, from 125kHz to

600kHz and calculate R

using the following formula:

where the switching frequency is in kHz and RT is in kΩ.

The MAX16831 is also capable of synchronizing to an

external clock signal ranging from 125kHz to 600kHz.

kHz

=×

500

25 Ω

MAX16831

REF

AGND

DIM

Figure 2. Creating a DIM Input Signal from REF

MAX16831

High-Voltage, High-Power LED Driver with

Analog and PWM Dimming Control

Maxim Integrated

Connect the clock signal to the RTSYNC input. The

MAX16831 synchronizes to the external clock signal

after the detection of five successive clock edges at

RTSYNC.

A buffered clock output, CLKOUT, is capable of driving

the RTSYNC input of an external PWM controller for

multichannel applications. CLKOUT is capable of dri-

ving capacitive loads up to 500pF.

Multichannel Configuration

The MAX16831 is capable of multichannel operation.

Connect CLKOUT to the SYNC input of an external

device to use the MAX16831 as a master clock signal.

Connect an external clock signal to RTSYNC to config-

ure the MAX16831 as a slave. To setup two or more

MAX16831 devices in a daisy-chain/peer-to-peer con-

figuration, drive the RTSYNC input of one MAX16831

with the CLKOUT buffer of another (Figure 3).

ILIM and HICCUP Comparator

SENSE

sets the peak current through the inductor for

switching. The differential voltage across R

SENSE

compared to the 200mV voltage trip limit of the current-

limit comparator, ILIM. Set the current limit 20% higher

than the peak switch current at the rated output power

and minimum voltage. Use the following equation to

calculate R

SENSE

= V

SENSE

/ (1.2 x I

PEAK

)

where V

SENSE

is the 200mV differential voltage

between SNS+ and SNS- and I

PEAK

is the peak induc-

tor current at full load and minimum input voltage.

When the voltage drop across R

SENSE

exceeds the

ILIM threshold, the MOSFET driver (DRV) terminates

the on-cycle and turns the switch off, reducing the cur-

rent through the inductor. The FET is turned back on at

the beginning of the next switching cycle.

When the voltage across R

SENSE

exceeds the 300mV

(typ) HICCUP threshold, the HIC comparator terminates

the on-cycle of the device, turning the switching

MOSFET off. Following a startup delay of 4ms (typ), the

MAX16831 re-initiates soft-start. The device will contin-

ue to operate in HICCUP mode until the overcurrent

condition is removed.

A built-in 40ns leading-edge blanking circuit of the cur-

rent-sense signal prevents these comparators from pre-

maturely terminating the on-cycle of the external

switching MOSFET (Q

). In some cases, this blanking

time may not be adequate and an additional RC filter

may be required to prevent spurious turn-off.

Load Current Sense

The load-sense resistor, R

, monitors the current

through the LEDs. The internal floating current-sense

amplifier, CSA, measures the differential voltage across

, and generates a voltage proportional to the LED

current through R

at CS. This voltage on CS is

referred to AGND. The closed loop regulates the LED

current to a value, I

LED

, given by the following equation:

LED

= 0.107V / R

Slope Compensation

The MAX16831 uses an internal ramp generator for

slope compensation. The internal ramp signal is reset

to zero at the beginning of each cycle and has a peak-

to-peak voltage of 120mV per switching cycle. Use an

external resistor, R

, to set the switching frequency,

, and calculate the slope of the compensating ramp,

SLOPE

, using the following equation:

SLOPE

= 120 x f

[mV/s]

where f

is the switching frequency in Hz. When the

MAX16831 is synchronized to an external clock, the

slope compensation ramp has a slope of 15mV/µs.

Internal Voltage-Error Amplifier (EAMP)

The MAX16831 includes a built-in voltage amplifier,

with tri-state output, which can be used to close the

feedback loop. The buffered output current-sense sig-

nal appears at CS, which is connected to the inverting

input, FB, of the error amplifier through resistor R

. The

noninverting input is connected to an internally trimmed

current reference.

The output of the error amplifier is controlled by the sig-

nal applied to DIM. When DIM is high, the output of the

amplifier is connected to COMP. The amplifier output is

open when DIM is low. This enables the integrating

MAX16831

RTSYNC

CLKOUT

RTSYNC

CLKOUT

MASTER/PEER

SLAVE/PEER

Figure 3. Master-Slave/Peer-Peer Clock Configuration

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P19

MAX16831ATJ/V+

Mfr. #:

Buy MAX16831ATJ/V+

Manufacturer:

Maxim Integrated

Description:

LED Lighting Drivers w/Analog & PWM Dimming Control

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MAX16831ATJ/V+

MAX16831ATJ/V+

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