A6263KLJTR-T Datasheet A6263KLJTR-T | P4-P6

Protected LED Array Driver

A6263

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Input Supply

Operating Input Voltage Range

6 – 50 V

Quiescent Current I

INQ

LAx pins connected to VIN – – 10 mA

Startup Time

VIN > 7 V to I

LA1

< –5 mA, R

REF

= 125 Ω – 20 – µs

Current Regulation

Reference Voltage V

IREF

0.7 mA < I

REF

< 8.8 mA 1.15 1.2 1.25 V

Reference Current Ratio G

6 V < V

< 40 V – 12.5 – A /A

Current Accuracy

ILAx

–10 mA > I

LAx

> –100 mA –5 ±4 5 %

Current Matching

IMLAx

–20 mA > I

LAx

> –100 mA, V

LAx

match to

within 1 V

– 5 10 %

Output Current I

LAx

REF

= 8 mA –105 –100 –95 mA

Maximum Output Current I

LAxmax

REF

= 9.2 mA – – –110 mA

Minimum Drop-out Voltage V

– V

LAx

, I

LAx

= –100 mA – – 800 mV

– V

LAx

, I

LAx

= –40 mA – – 660 mV

Protection

Short Detect Voltage V

SCD

Measured at LAx 1.2 – 1.8 V

Short Circuit Source Current I

SCS

Short present from LAx to GND –2 –0.8 –0.5 mA

Short Release Voltage V

SCR

Measured at LAx – – 1.9 V

Short Release Voltage Hysteresis V

SChys

SCR

– V

SCD

200 – 500 mV

Thermal Monitor Activation Temperature T

with I

SEN

= 90% 95 115 130 °C

Thermal Monitor Slope dI

SEN

/dT

SEN

= 50% –3.5 –2.5 –1.5 %/°C

Thermal Monitor Low Current

Temperature

at I

SEN

= 25% 120 135 150 °C

Overtemperature Shutdown T

Temperature increasing – 170 – °C

Overtemperature Hysteresis T

Jhys

Recovery = T

– T

Jhys

– 15 – °C

For input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.

Function is correct but parameters are not guaranteed outside the general limits (7 to 40 V).

Ensured by design and characterization, not production tested.

ILAx

= 100 × [( | I

LAx

| × R

REF

/ 15 ) –1], with I

LAx

in mA and R

REF

in kΩ.

IMLA

= 100 × max ( | I

LAx

– I

LA(AV)

| ) / I

LA(AV)

, where I

LA(AV)

is the average current of all active outputs.

ELECTRICAL CHARACTERISTICS

Valid at T

= 25°C, V

= 7 to 40 V; indicates specifications valid across the full operating

temperature range with T

= T

= –40°C to 125°C and typical specifications at T

= 25°C; unless otherwise specified

Characteristics Symbol Test Conditions Min. Typ. Max. Unit

Protected LED Array Driver

A6263

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Functional Description

The A6263 is a linear current regulator that is designed to pro-

vide drive current and protection for parallel strings of series-

connected high brightness LEDs. It provides up to 4 matched pro-

grammable current outputs at up to 100 mA, with low minimum

dropoutvoltagesbelowthemainsupplyvoltage.For12Vpower

net applications, optimum performance is achieved when driving

4 strings of 1 to 3 LEDs, at current up to 100 mA per string.

Current regulation is maintained and the LEDs protected during a

short-to-ground at any point in the LED string. A short-to-ground

on any regulator output terminal disables that offending string

only. Similarly, in the case of an open output pin or an open-LED

fault, all other LED strings remain in regulation. Individual out-

putscanbedisabledbyconnectingtheoutputtoVIN.Multiple

outputs can be connected in parallel to drive higher current LED

strings.

Integrated thermal management reduces the regulated current

level at high internal junction temperatures to limit power dis-

sipation. This thermal threshold is programmable and can be

disabled if necessary.

Pin Functions

VIN Supply to the control circuit and current regulators. A small

value ceramic bypass capacitor, typically 100 nF, should be con-

nected from close to this pin to the GND pin.

GND Ground reference connection. Should be connected directly

to the ground plane of the circuit board.

IREF1.2VreferencetosetLEDcurrent.Connectresistor,R

REF

to GND to set reference current and thereby LED current.

THTH Sets the thermal monitor threshold, T

JM

, where the output

current starts to reduce with increasing temperature. Connecting

THTH directly to GND will disable the thermal monitor function.

LA[1:4] Current source connected to the anode of the first LED

ineachstring.ConnectdirectlytoVINtodisabletherespective

output. In this document “LAx” indicates any one of the outputs.

LED Current Level

The LED current is controlled by 4 matching linear current regu-

lators,betweentheVINpinandeachoftheLAxoutputs.The

basic equation that determines the nominal output current at each

LAx pin is:

LAx

REF

(1)

where I

LAx

isinmAandR

REF

isinkΩ.

The output current may be reduced from the set level by the ther-

mal monitor circuit.

Conversely the reference resistors may be calculated from:

LAx

REF

(2)

where I

LAx

isinmAandR

REF

isinkΩ.

For example, where the required current is 90 mA for both chan-

nels the resistor value will be:

= =

REF

0.167 kΩ

These equations completely define the output currents with

respect to the setting resistors. However, for further reference, a

more detailed description of the internal reference current calcu-

lations is included below.

It is important to note that because the A6263 is a linear regu-

lator, the maximum regulated current is limited by the power

dissipation and the thermal management in the application. All

current calculations assume adequate heatsinking for the dissi-

pated power. Thermal management is at least as important as the

electrical design in all applications. In high current high ambient

temperature applications the thermal management is the most

important aspect of the systems design. The application section

below provides further detail on thermal management and the

associated limitations.

Operation with Fewer LED Strings or Higher Currents

The A6263 may be configured to use fewer than all four LED

strings, either by connecting outputs together for higher currents,

orbyconnectingtheoutputdirectlytoVINtodisabletheregula-

tor for that output. It is also acceptable, though not recommended,

to leave an unused LAx pin floating.

Protected LED Array Driver

A6263

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Safety Features

The A6263 includes several features to ensure safe operation and

to protect the LEDs and the IC:

•ThecurrentregulatorsbetweenVINandeachLAxoutputpro-

vide a natural current limit due to the regulation.

• Each LAx output includes a short-to-ground detector that will

disable the output to limit the dissipation.

• An open circuit on any output will disable the affected string

only.

• The thermal monitor reduces the regulated current as the tem-

perature rises above a programmable thermal threshold.

• Thermal shutdown completely disables the outputs under ex-

treme overtemperature conditions.

Temperature Monitor

A temperature monitor function reduces the LED current as the

silicon junction temperature of the IC increases (see figure 2). By

mounting the A6263 on the same thermal substrate as the LEDs,

this feature can also be used to limit the dissipation of the LEDs.

As the junction temperature of the A6263 increases, the regulated

current level is reduced, reducing the dissipated power in the

A6263 and in the LEDs. The current is reduced from the 100%

level at typically 2.5% per degree Celsius until the point at which

the current drops to 25% of the full value, defined at T

. Above

this temperature the current will continue to reduce at a lower

rate until the temperature reaches the overtemperature shutdown

threshold temperature, T

The temperature at which the current reduction begins can be

adjustedbychangingthevoltageontheTHTHpin.WhenTHTH

is left open the temperature at which the current reduction begins

is defined as the thermal monitor activation temperature, T

and is specified, in the Electrical Characteristics table, at the 90%

current level.

JM

willincreaseasthevoltageattheTHTHpin,V

THTH

, is

reduced and is defined as approximately:

0.0039

(°C)

1.46 –V

THTH

(3)

AresistorconnectedbetweenTHTHandGNDwillreduceV

THTH

and increase T

. A resistor connected between THTH and a refer-

encesupplygreaterthan1VwillincreaseV

THTH

and reduce T

Figure 3 shows how the nominal value of the thermal monitor

activation temperature varies with the voltage at THTH and with

eitherapull-downresistor,R

, to GND or with a pull-up resis-

tor,R

,to3Vandto5V.

In extreme cases, if the chip temperature exceeds the overtem-

perature limit, T

, all regulators will be disabled. The tempera-

ture will continue to be monitored and the regulators re-activated

when the temperature drops below the threshold provided by the

specified hysteresis.

100

70 90 110

Junction Temperature, T

(°C)

Relative Sense Current (%)

130 150 170

Figure 2. Temperature monitor current reduction

250

200

150

100

1.3

1.2

1.1

1.0

0.9

0.8

THTH

70 80 90 110100

Thermal Monitor Activation Temperature, T

(°C)

(kΩ)

THTH

(V)

130120 150140

pull-up

to 5 V

pull-up

to 3 V

pull-down

to GND

Figure 3. T

versus a pull-up or pull-down resistor, R

, and V

THTH

P1-P3 P4-P6 P7-P9 P10-P11

A6263KLJTR-T

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