A6262KLYTR-T - Allegro MicroSystems Europe Ltd.

Description

The A6262 is a linear, programmable current regulator providing

up to 100 mA from each of four outputs to drive arrays of high

brightness LEDs. The regulated LED current from each output,

accurate to 5%, is set by a single reference resistor. Current

matching in each string is better than 10% without the use of

ballast resistors. Driving LEDs with constant current ensures

safe operation with maximum possible light output.

Output control is provided by an enable input, giving direct

control for PWM applications, and by a debounced switch

input, proving an on/off toggle action.

Optimum performance is achieved driving 1 to 3 LEDs in

each string: up to 4 strings at 100 mA each. Outputs can be

connected in parallel or left unused as required.

Short detection is provided to protect the LEDs and the A6262

during a short-to-ground at any LED output pin. The output

will automatically resume the regulated current when the short

is removed.

A temperature monitor is included to reduce the LED drive

current if the chip temperature exceeds an adjustable thermal

threshold.

The device packages are a 10-pin MSOP (suffix LY), and

a 16-pin TSSOP (LP), both with exposed pad for enhanced

thermal dissipation. They are lead (Pb) free, with 100% matte

tin leadframe plating.

A6262-DS, Rev. 6

Features and Benefits

 AEC Q-100 qualified

 Total LED drive current up to 400 mA

 Current shared equally up to 100 mA by 4 strings

 6 to 50 V supply

 Low dropout voltage

 LED output short-to-ground and thermal protection

 On/off toggle switch input

 Enable input for PWM control

 Current slew rate limit during PWM

 Current set by reference resistor

 Automotive temperature range

Applications:

Typical Application Diagram

A6262

Automotive LED Array Driver

 Dome light, map light, space lighting, mood lighting

A6262

–

LA1

VIN

Automotive

12 V power net

PWM dimming

input from LCU

LA2

LA3

LA4

On/Off

100 mA

IREF

THTH

GND

PAD

Packages

Not to scale

10-pin MSOP with

exposed thermal pad

(suffix LY)

16-pin TSSOP with

exposed thermal pad

(suffix LP)

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Absolute Maximum Ratings1

Characteristic Symbol Notes Rating Unit

Load Supply Voltage VIN –0.3 to 50 V

Pin EN –0.3 to 50 V

Pins LA[1:4] –0.3 to 50 V

Pins IREF, THTH, SW –0.3 to 6.5 V

Ambient Operating Temperature

Range2TAK temperature range –40 to 125 °C

Maximum Continuous Junction

Temperature TJ(max) 150 °C

Transient Junction Temperature TtJ

Over temperature event not exceeding 10 s, lifetime duration

not exceeding 10 h, guaranteed by design characterization 175 °C

Storage Temperature Range Tstg –55 to 150 °C

1With respect to GND.

2Limited by power dissipation.

Selection Guide

Part Number Ambient Operating

Temperature, TA (°C) Packing Package

A6262KLPTR-T

–40 to 125 4000 pieces per 13-in. reel

16-pin TSSOP with exposed thermal pad,

4.4 × 5 mm case

A6262KLYTR-T 10-pin MSOP with exposed thermal pad,

3 × 3 mm case

Thermal Characteristics*may require derating at maximum conditions, see application information

Characteristic Symbol Test Conditions* Value Unit

Package Thermal Resistance

(Junction to Ambient) RJA

LP package

On 4-layer PCB based on JEDEC standard 34 ºC/W

On 2-layer PCB with 3.8 in.2 of copper area each side 43 ºC/W

LY package

On 4-layer PCB based on JEDEC standard 48 ºC/W

On 2-layer PCB with 2.5 in.2 of copper area each side 48 ºC/W

Package Thermal Resistance

(Junction to Pad) RJP 2 ºC/W

*To be verified by characterization. Additional thermal information available on the Allegro™ website.

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

LA1

VIN

VBAT

Current

Regulators

GND

PAD

Tem p

Comp

Tem p

Monitor

Slew

Limit

Current

Reference

Control

Logic

LA2

LA3

LA4

IREF

RREF

RTH

THTH

Deglitch

Functional Block Diagram

Pin-out Diagrams

LP Package

LY Package

THTH

IREF

GND

LA1

LA2

VIN

LA4

LA3

PAD

THTH

IREF

GND

LA1

LA2

VIN

LA4

LA3

PAD

Terminal List Table

Name

Number

FunctionLP LY

EN 13 9 Enable

SW 14 10 Switch input

GND 5 3 Ground reference

IREF 4 2 Current reference

LA1 6 4 LED anode (+) connection 1

LA2 7 5 LED anode (+) connection 2

LA3 10 6 LED anode (+) connection 3

LA4 11 7 LED anode (+) connection 4

NC 1,2,8,

9,15,16 n.a. No connection; connect to GND

PAD – – Exposed thermal pad

THTH 3 1 Thermal threshold

VIN 12 8 Supply

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Supply and Reference

VIN Functional Operating Range26 – 50 V

VIN Quiescent Current IINQ LA[1:4] connected to VIN – – 10 mA

VIN Sleep Current IINS EN = GND, VIN = 16 V – – 15 A

Startup Time tON VIN > 7 V to ILA1 < –5 mA, RREF = 125 51530 s

Current Regulation

Reference Voltage VIREF 0.7 mA < IREF < 8.8 mA 1.15 1.2 1.25 V

Reference Current Ratio GH

ILAx / IREF – 12.5 – –

Current Accuracy3EILAx –10 mA > ILAx > –100 mA –5 ±4 5 %

Current Matching4EIMLAx

–20 mA > ILAx > –100 mA,

VLAx match to within 1 V – 5 10 %

Output Current, High Level ILAx

EN = high – GH ×

IREF

––

IREF = 8 mA, EN = high –105 –100 –95 mA

Maximum Output Current ILAxmax IREF = 9.2 mA, EN = high – – –110 mA

Minimum Drop-out Voltage VDO

VIN – VLAx , ILAx = –100 mA – – 800 mV

VIN – VLAx , ILAx = –40 mA – – 660 mV

Current Slew Time Current rising or falling between 10% and 90% 50 80 110 s

Logic Inputs EN and SW

Input Low Voltage VIL – – 0.8 V

Input High Voltage VIH 2–– V

Input Hysteresis (EN pin) VIhys 150 350 – mV

Pull-Down Resistor (EN pin) RPD –50– k

Pull-Up Current (SW pin) IPU – 100 – A

SW Input Debounce Time tSW 10–50ms

Protection

Short Detect Voltage VSCD Measured at LAx 1.2 – 1.8 V

Short Circuit Source Current ISCS Short present LAx to GND –2 –0.8 –0.5 mA

Short Release Voltage VSCR Measured at LAx – – 1.9 V

Short Release Voltage Hysteresis VSChys VSCR – VSCD 200 – 500 mV

Thermal Monitor Activation Temperature TJM TJ with ISEN = 90%, THTH open 95 115 130 °C

Thermal Monitor Slope dISEN/dTJISEN = 50%, THTH open –3.5 –2.5 –1.5 %/°C

Thermal Monitor Low Current

Temperature TJL TJ at ISEN = 25%, THTH open 120 135 150 °C

Overtemperature Shutdown TJF Temperature increasing – 170 – °C

Overtemperature Hysteresis TJhys Recovery = TJF – TJhys –15– °C

1For input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.

2Function is correct but parameters are not guaranteed outside the general limits (7 to 40 V).

3When EN = high, EILAx = 100 × [( | ILAx | × RREF / 15 ) –1], with ILAx in mA and RREF in k.

4EIMLA = 100 × [ max ( | ILAx– ILA(AV) | ) / ILA(AV) ] , where ILA(AV) is the average current of all active outputs.

ELECTRICAL CHARACTERISTICS1 Valid at TJ = –40°C to 150°C, VIN = 7 to 40 ; unless otherwise noted

Characteristics Symbol Test Conditions Min. Typ. Max. Unit

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Functional Description

The A6262 is a linear current regulator that is designed to pro-

vide drive current and protection for parallel strings of series-

connected high brightness LEDs in automotive applications. It

provides up to four matched programmable 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.

The A6262 is specifically designed for use in internal illumina-

tion applications where the LED activity is controlled by a PWM

signal, by a logic signal, or by a push-to-make, ground-connected

switch.

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 will disable that output until the

short is removed. Open load on any output will be ignored.

Integrated thermal management reduces the regulated current

level at high internal junction temperatures to limit power dis-

sipation.

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 negative supply.

EN Logic input to enable LED current output. This provides a

direct on/off action and can be used for direct PWM control. The

EN input overrides the SW input when EN is high. When EN

transitions from high to low, SW input logic is reset to off.

SW Logic input to toggle LED current output on and off. A

single push-to-make switch between SW and GND will provide

push-to-make/push-to-break, on/off toggle action. The SW input

is debounced by typically 30 ms and is internally pulled to typi-

cally 3 V, with approximately 100 A.

IREF 1.2 V reference to set current reference. Connect resistor,

RREF

, to GND to set reference current.

THTH Sets the thermal monitor threshold, TJM

, 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 a matching linear current regu-

lator between the VIN pin and each of the LAx outputs. The basic

equation that determines the nominal output current at each LAx

pin is:

Given EN = high,

ILAx =RREF

(1)

where ILAx is in mA and RREF is in k; K is 15.

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

mal monitor circuit.

Conversely the reference resistors may be calculated from:

ILAx

RREF

(2)

where ILAx is in mA and RREF is in k.

For example, where the required current is 90 mA for all four

channels the resistor value will be:

RREF 167 

It is important to note that because the A6262 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 A6262 may be configured to use fewer than the maximum

quantity of LED strings: by connecting outputs together for

higher currents, by leaving the outputs open, or by connecting the

output directly to VIN to disable the regulator for that output.

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Sleep Mode

When EN is held low the A6262 will be in shutdown mode and

all sections will be in a low power sleep mode. The input current

will be typically less than 10 A. This means that the complete

circuit, including LEDs, may remain connected to the power sup-

ply under all conditions.

Safety Features

The circuit includes several features to ensure safe operation and

to protect the LEDs and the A6262:

• 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.

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

perature rises.

• Thermal shutdown completely disables the outputs under ex-

treme overtemperature conditions.

Short Circuit Detection A short to ground on any LED

cathode (figure 1A) will not result in a short fault condition. The

current through the remaining LEDs will remain in regulation and

the LEDs will be protected. Due to the difference in the voltage

drop across the LEDs, as a result of the short, the current match-

ing in the A6262 may exceed the specified limits.

Any LAx output that is pulled below the short detect voltage (fig-

ure 1B) will disable the regulator on that output. A small current

will be sourced from the disabled output to monitor the short and

detect when it is removed. When the voltage at LAx rises above

the short detect voltage, the regulator will be re-enabled.

A shorted LED (figure 1C) will not result in a short fault condi-

tion. The current through the remaining LEDs will remain in

regulation and the LEDs will be protected. Due to the difference

in the voltage drop across the LEDs, as a result of the short, the

current matching in the A6262 may exceed the specified limits.

A short between LEDs in different strings (figure 1D) will not

result in a short fault condition. The current through the remain-

ing LEDs will remain in regulation and the LEDs will be pro-

tected. The current will be summed and shared by the affected

strings. Current matching in the strings will then depend on the

LED forward voltage differences.

Temperature Monitor A temperature monitor function,

included in the A6262, reduces the LED current as the silicon

junction temperature of the A6262 increases (see figure 2). By

mounting the A6262 on the same thermal substrate as the LEDs,

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

A6262

VIN

GND

LA2

LA1

LA3

LA4

A6262

VIN

GND

LA2

LA1

LA3

LA4

A6262

VIN

GND

LA2

LA1

LA3

LA4

A6262

VIN

GND

LA2

LA1

LA3

LA4

A. Any LED cathode short to ground.

Current remains regulated in

non-shorted LEDs. Matching may be

affected.

B. Any LAx output short to ground.

Shorted output is disabled. Other

outputs remain active.

C. Current remains regulated.

Matching may be affected.

Only the shorted LED is inactive.

D. Short between LEDs in different

strings. Current remains regulated.

Current is summed and shared by

affected strings. Intensity match

dependent on voltage binning.

Figure 1. Short circuit conditions.

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

As the junction temperature of the A6262 increases, the regulated

current level is reduced, reducing the dissipated power in the

A6262 and in the LEDs. The current is reduced from the 100%

level at typically 4% per degree Celsius until the point at which

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

. Above

this temperature the current will continue to reduce at a lower

rate until the temperature reaches the overtemperature shutdown

threshold temperature, TJF.

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, TJM, and

is specified, in the characteristics table, at the 90% current level.

TJM will increase as the voltage at the THTH pin, VTHTH , is

reduced and is defined as approximately:

0.0039

TJM (°C)

1.46 –VTHTH

(3)

A resistor connected between THTH and GND will reduce VTHTII

and increase TJM. A resistor connected between THTH and a refer-

ence supply greater than 1 V will increase VTHTH and reduce TJM.

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, RTH, to GND or with a pull-up resis-

tor, RTH

, to 3 V and to 5 V.

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

perature limit, TJF

, 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.

Note that it is possible for the A6262 to transition rapidly

between thermal shutdown and normal operation. This can hap-

pen if the thermal mass attached to the exposed thermal pad is

small and TJM is increased to close to the shutdown temperature.

The period of oscillation will depend on TJM

, the dissipated

power, the thermal mass of any heatsink present, and the ambient

temperature.

100

TJM

TJL

TJF

70 90 110

Junction Temperature, TJ (°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

VTHTH

70 80 90 110100

Thermal Monitor Activation Temperature, TJM (°C)

RTH (k)

VTHTH (V)

130120 150140

RTH pull-up

to 5 V

RTH pull-up

to 3 V

RTH pull-down

to GND

Figure 3. TJM versus a pull-up or pull-down resistor, RTH, and VTHTH.

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Application Information

Power Dissipation

The most critical design considerations when using a linear regu-

lator such as the A6262 are the power produced internally as heat

and the rate at which that heat can be dissipated.

There are three sources of power dissipation in the A6262:

• The quiescent power to run the control circuits

• The power in the reference circuit

• The power due to the regulator voltage drop

The elements relating to these dissipation sources are illustrated

in figure 4.

Quiescent Power The quiescent power is the product of the

quiescent current, IINQ

, and the supply voltage, VIN , and is not

related to the regulated current. The quiescent power, PQ, is there-

fore defined as:

PQ = VIN × IINQ (4)

Reference Power The reference circuit draws the reference

current from the supply and passes it through the reference resis-

tor to ground. The reference current is 8% of the output current

on any one active output. The reference circuit power is the prod-

uct of the reference current and the difference between the supply

voltage and the reference voltage, typically 1.2 V. The reference

power, PREF , is therefore defined as:

PREF =RREF

(VIN – VREF) × VREF

(5)

Regulator Power In most application circuits the largest dis-

sipation will be produced by the output current regulators. The

power dissipated in each current regulator is simply the product

of the output current and the voltage drop across the regulator.

The total current regulator dissipation is the sum of the dissipa-

tion in each output regulator. The regulator power for each output

is defined as:

PREGx =(VIN – VLEDx ) × ILEDx

(6)

where x is 1, 2, 3, or 4.

Note that the voltage drop across the regulator, VREG , is always

greater than the specified minimum drop-out voltage, VDO

. The

output current is regulated by making this voltage large enough

to provide the voltage drop from the supply voltage to the total

forward voltage of all LEDs in series, VLED .

The total power dissipated in the A6262 is the sum of the quies-

cent power, the reference power, and the power in each of the our

regulators:

PDIS =PQ + PREF

+ PREGA + PREGB + PREGC + PREGD

(7)

The power that is dissipated in each string of LEDs is:

PLEDx =VLEDx × ILEDx

(8)

where x is A, B, C, or D, and VLEDx is the voltage across all

LEDs in the string.

Figure 4. Internal power dissipation sources.

A6262

LAx

ILAx

IINQ

IREF

VIN

GND

IREF

RREF

VREF

VLED

VREG

VIN

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

From these equations (and as illustrated in figure 5) it can be seen

that, if the power in the A6262 is not limited, then it will increase

as the supply voltage increases but the power in the LEDs will

remain constant.

Dissipation Limits

There are two features limiting the power that can be dissipated

by the A6262: thermal shutdown and thermal foldback.

Thermal Shutdown If the thermal foldback feature is disabled

by connecting the THTH pin to GND, or if the thermal resistance

from the A6262 to the ambient environment is high, then the

silicon temperature will rise to the thermal shutdown threshold

and the current will be disabled. After the current is disabled the

power dissipated will drop and the temperature will fall. When

the temperature falls by the hysteresis of the thermal shutdown

circuit, then the current will be re-enabled and the temperature

will start to rise again. This cycle will repeat continuously until

the ambient temperature drops or the A6262 is switched off. The

period of this thermal shutdown cycle will depend on several

electrical, mechanical, and thermal parameters, and could be from

a few milliseconds to a few seconds.

Thermal Foldback If there is a good thermal connection to the

A6262, then the thermal foldback feature will have time to act.

This will limit the silicon temperature by reducing the regulated

current and therefore the dissipation.

The thermal monitor will reduce the LED current as the tempera-

ture of the A6262 increases above the thermal monitor activation

temperature, TJM , as shown in figure 6. The figure shows the

operation of the A6262 with 4 strings of 3 red LEDs, each string

running at 50 mA. The forward voltage of each LED is 2.3 V and

the graph shows the current as the supply voltage increases from

14 to 17 V. As the supply voltage increases, without the thermal

foldback feature, the current would remain at 50 mA, as shown by

the dashed line. The solid line shows the resulting current decrease

as the thermal foldback feature acts.

If the thermal foldback feature did not affect LED current, the

current would increase the power dissipation and therefore the

silicon temperature. The thermal foldback feature reduces power

in the A6262 in order to limit the temperature increase, as shown

in figure 7. The figure shows the operation of the A6262 under

the same conditions as figure 6. That is, 4 strings of 3 red LEDs,

each string running at 50 mA with each LED forward voltage at

Figure 5. Power Dissipation versus Supply Voltage

3.0

2.5

2.0

1.5

1.0

0.5

89 1110

Supply Voltage, VIN (V)

Power Dissipation, PD (W)

1312 161514

LED Power

A6262 Power 4 Strings

VLED = 6.9 V

ILED = 50 mA

Figure 6. LED current versus Supply Voltage

Figure 7. Junction Temperature versus Supply Voltage

Without thermal monitor

With thermal monitor

14.0 14.5 15.0 16.0 17.015.5

Supply Voltage, VIN (V)

ILED (mA)

16.5

4 Strings

VLED = 6.9 V

ILED = 50 mA

TA = 50°C

130

125

120

115

110

105

100

Without thermal monitor

With thermal monitor

14.0 14.5 15.0 16.0 17.015.5

Supply Voltage, VIN (V)

TJ (°C)

16.5

4 Strings

VLED = 6.9 V

ILED = 50 mA

TA = 50°C

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

2.3 V. The graph shows the temperature as the supply voltage

increases from 14 to 17 V. Without the thermal foldback feature

the temperature would continue to increase up to the thermal

shutdown temperature as shown by the dashed line. The solid line

shows the effect of the thermal foldback function in limiting the

temperature rise.

Figures 6 and 7 show the thermal effects where the thermal

resistance from the silicon to the ambient temperature is 40°C/W.

Thermal performance can be enhanced further by using a signifi-

cant amount of thermal vias as described below.

Thermal Dissipation

The amount of heat that can pass from the silicon of the A6262

to the surrounding ambient environment depends on the thermal

resistance of the structures connected to the A6262. The thermal

resistance, RJA

, is a measure of the temperature rise created by

power dissipation and is usually measured in degrees Celsius per

watt (°C/W).

The temperature rise, T, is calculated from the power dissipated,

, and the thermal resistance, RJA

, as:

T = PD × RJA (9)

A thermal resistance from silicon to ambient, RJA

, of approxi-

mately 30°C/W (LP package) or 34°C/W (LY package) can be

achieved by mounting the A6262 on a standard FR4 double-sided

printed circuit board (PCB) with a copper area of a few square

inches on each side of the board under the A6262. Multiple

thermal vias, as shown in figure 8, help to conduct the heat from

the exposed pad of the A6262 to the copper on each side of the

board. The thermal resistance can be reduced by using a metal

substrate or by adding a heatsink.

Supply Voltage Limits

In many applications, especially in automotive systems, the avail-

able supply voltage can vary over a two-to-one range, or greater

when double battery or load dump conditions are taken into con-

sideration. In such systems is it necessary to design the applica-

tion circuit such that the system meets the required performance

targets over a specified voltage range.

To determine this range when using the A6262 there are two

limiting conditions:

• For maximum supply voltage the limiting factor is the power

that can be dissipated from the regulator without exceeding the

temperature at which the thermal foldback starts to reduce the

output current below an acceptable level.

• For minimum supply voltage the limiting factor is the maximum

drop-out voltage of the regulator, where the difference between

the load voltage and the supply is insufficient for the regulator

to maintain control over the output current.

Minimum Supply Limit: Regulator Saturation Voltage

The supply voltage, VIN

, is always the sum of the voltage drop

across the high-side regulator, VREG , and the forward voltage of

the LEDs in the string, VLED, as shown in figure 4.

VLED is constant for a given current and does not vary with

supply voltage. Therefore VREG provides the variable difference

between VLED and VIN . VREG has a minimum value below which

the regulator can no longer be guaranteed to maintain the output

current within the specified accuracy. This level is defined as the

regulator drop-out voltage, VDO.

The minimum supply voltage, below which the LED current does

not meet the specified accuracy, is therefore determined by the

sum of the minimum drop-out voltage, VDO , and the forward

voltage of the LEDs in the string, VLED . The supply voltage must

Figure 8. Board via layout for thermal dissipation: (top) LP

package and (bottom) LY package.

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

always be greater than this value and the minimum specified sup-

ply voltage, that is:

VIN > VDO + VLED, and

VIN > VIN

(min) (10)

As an example, consider the configuration used in figures 6 and

7 above, namely 4 strings of 3 red LEDs, each string running at

50 mA, with each LED forward voltage at 2.3 V. The minimum

supply voltage will be approximately:

VIN(min) = 0.55 + (3 × 2.3) = 7.45 V

Maximum Supply Limit: Thermal Limitation As described

above, when the thermal monitor reaches the activation tempera-

ture, TJM (due to increased power dissipation as the supply volt-

age rises), the thermal foldback feature causes the output current

to decrease. The maximum supply voltage is therefore defined as

the voltage above which the LED current drops below the accept-

able minimum.

This can be estimated by determining the maximum power that

can be dissipated before the internal (junction) temperature of the

A6262 reaches TJM.

Note that, if the thermal monitor circuit is disabled (by connect-

ing the THTH pin to GND), then the maximum supply limit will

be the specified maximum continuous operating temperature,

150°C.

The maximum power dissipation is therefore defined as:

PD(max) =RJA

T(max)

(11)

where T(max) is difference between the thermal monitor activa-

tion temperature, TJM

, of the A6262 and the maximum ambient

temperature, TA(max), and RJA is the thermal resistance from the

internal junctions in the silicon to the ambient environment.

If minimum LED current is not a critical factor, then the maxi-

mum voltage is simply the absolute maximum specified in the

parameter tables above.

Application Examples

Operation with High-Side PWM Supply In some filament

bulb replacement applications the supply may be provided by a

PWM-driven high-side switch. The A6262 can be used in this

application by simply connecting EN to VIN.

The toggle action of the SW input will be reset to off at each

power-up. In addition, in all cases when EN is high, the EN input

will override the SW toggle status and enable the outputs. At the

high-to-low transition of EN, the SW toggle will always be reset

to the off state.

When power is applied, there will be a short startup delay, tON ,

before the current starts to rise. The rise time of the current will

be limited by the internal current slew rate control.

Figures 9a to 9c show application circuit options, including a

higher voltage supply, and combinations of outputs tied together

and disabled.

Operation with both EN and SW In some applications it

may be required to utilize the functionality of both the EN input

and the SW input. For example in dome lighting, where a manual

switch may be used to turn the light on and the lighting control

unit may dim the light to off (see figure 10). In these cases it is

important to understand the interaction of the two control inputs.

• In all cases, when EN is high the EN input will override the SW

toggle status and enable the outputs.

• When EN is low the SW input can be used to toggle the outputs

on and off.

• The only time there is any interaction between the EN input and

the SW toggle is the high-to-low transition of EN, where the

SW toggle will always be reset to the off state.

• The SW toggle will also be reset to the off state at power-up.

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

A6262

–

VIN

12 V PWM

high-side drive

GND

LA1

LA2

LA3

LA4

LA1

LA2

LA3

LA4

LA1

LA2

LA3

LA4

LA1

LA2

LA3

LA4

IREF

THTH

A6262

–

VIN

Automotive

24 V power net

GND

IREF

THTH

A6262

–

VIN

Automotive

12 V power net

GND

IREF

THTH

On/Off

A6262

–

VIN

Automotive

24 V power net

PWM dimming

input from LCU

GND

IREF

THTH

On/Off

Figure 10. Typical applications using SW and EN together

Figure 9. Typical applications with various supply and output options.

B. Higher voltage operation

C. Mix of output combinations

A. High brightness (HB) LED incandescent lamp replacement

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Package LP, 16-Pin TSSOP with Exposed Thermal Pad

1.20 MAX

0.15

0.00

0.30

0.19

0.20

0.09

8º

0º

0.60 ±0.15

1.00 REF

SEATING

PLANE

C0.10

16X

0.65 BSC

0.25 BSC

5.00±0.10

4.40±0.10 6.40±0.20

GAUGE PLANE

SEATING PLANE

ATerminal #1 mark area

For Reference Only; not for tooling use (reference MO-153 ABT)

Dimensions in millimeters

Dimensions exclusive of mold flash, gate burrs, and dambar protrusions

Exact case and lead configuration at supplier discretion within limits shown

Exposed thermal pad (bottom surface); dimensions may vary with device

6.10

0.65

0.45

1.70

3.00

Reference land pattern layout (reference IPC7351

SOP65P640X110-17M);

All pads a minimum of 0.20 mm from all adjacent pads; adjust as

necessary to meet application process requirements and PCB layout

tolerances; when mounting on a multilayer PCB, thermal vias at the

exposed thermal pad land can improve thermal dissipation (reference

EIA/JEDEC Standard JESD51-5)

PCB Layout Reference View

Branded Face

3±0.05

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Package LY, 10-Pin MSOP with Exposed Thermal Pad

Terminal #1 mark area

Gauge Plane

Seating Plane

0.86 ±0.05

SEATING

PLANE

0.50

REF

0.25

0.53 ±0.10

0.15 ±0.05

0.05

0.15

0° to 6°

3.00 ±0.10

3.00 ±0.10 4.88 ±0.20

1.98

1.73

0.27

0.18

For Reference Only; not for tooling use (reference JEDEC MO-187)

Dimensions in millimeters

Dimensions exclusive of mold flash, gate burrs, and dambar protrusions

Exact case and lead configuration at supplier discretion within limits shown

Exposed thermal pad (bottom surface)

Automotive LED Array Driver

A6262

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

For the latest version of this document, visit our website:

www.allegromicro.com

Allegro MicroSystems, LLC reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to

permit improvements in the per for mance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that

the information being relied upon is current.

Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the

failure of that life support device or system, or to affect the safety or effectiveness of that device or system.

The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, LLC assumes no re spon si bil i ty for its

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Revision History

Revision Revision Date Description of Revision

Rev. 6 June 24, 2013 Update Features List, figure 5