STTH3002G Datasheet AL8400QSE-7, AL8400SE-7, STTH3002G | P10-P12

AL8400/ AL8400Q

Document number: DS35115 Rev. 4 - 2

10 of 13

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August 2012

AL8400 /

A

L8400Q

Application Information (cont.)

MOSFET Example Choosing R

B

and C

L

(cont.)

R

Bmax

The minimum recommended I

OUT

for AL8400 is 0.3mA.

The maximum V

GS

is not stated explicitly, but from the datasheet graphs (Figures 8 and 9) it is expected to be approximately 3.8V at -50°C.

=

−−

=

minOUT

FBmaxGSminCC

maxB

I

VVV

R

=

−−

=

mA3.0

V2.0V8.3V4.11

24.7k

To ensure that the output capability of the AL8400 is not exceeded at maximum V

IN

and minimum V

GS

these values should be substituted back

into the R

B

equation to determine the minimum allowable value for R

B

.

R

Bmin

The maximum recommended I

OUT

for the AL8400 is 15mA. The minimum V

GS

is about 1V and assuming V

CCmax

= 8.4V:

maxOUT

FBminGSmaxCC

minB

I

VVV

R

−−

=

mA15

V2.0V1V6.12 −−

= 480

this is less than 12k and so the AL8400 output current is within its ratings.

Figure 8 Typical Transfer Characteristics

Figure 9 Normalised Curves and Temperature

Assuming V

GS

~ 3V and choosing an R

B

= 8.2k satisfies the requirements for the AL8400 conformance and sets approximately 1mA in the OUT

pin. The required compensation capacitor can therefore be calculated from:

F243.0

k2.8

ms2

C

L

μ≈

Ω

≈

Æ 220nF

The value of R

SET

is V

REF

/I

LED

R

SET

= 0.2/0.2 = 1

Finally, the maximum power dissipation of the external MOSFET is:

P

TOT

= I

LED

x V

DSMAX

=

I

LED

x (V

CCmax

– V

LEDMIN

– V

FB

)

= 0.2 x( 12.6 – 9 -0.2) = 0.68W

This determines the package choice (θ

JA

) in order to keep the junction temperature below the maximum value allowed.

T

J

= T

A

+ P

TOT

x θ

JA

= 60 + 0.68 x 62.5 = +102.5˚C

AL8400/ AL8400Q

Document number: DS35115 Rev. 4 - 2

11 of 13

www.diodes.com

August 2012

AL8400 /

A

L8400Q

Application Information (cont.)

High Voltage Operation

The AL8400 also provides the capability to drive longer LED chains as the voltage across the LED chain is determined by the external switch.

The lower supply voltage for the AL8400 can be derived from the supply to the LED chain either by putting a series resistor to the AL8400’s V

CC

pin and putting a suitable zener diode from its V

CC

to GND Figure 10 or by tapping its V

CC

from the LED chain Figure 11.

Figure 10 High Voltage Operation with Zener Diode from VIN

Equations 1 and 2 (from page 7) now transform into:

LED Circuit Path:

1. V

IN

= (V

LED

+ V

CE

+ V

FB

)

Control Dri

v

e Circuit Path

2. V

CC

= (V

RB

+ V

BE

+ V

FB

)

When the supply voltage for the AL8400 is derived using a zener diode, care has to be taken in dimensioning the resistor R1. The current taken

through R1 from V

IN

has to be large enough to polarize the zener, bias the AL8400 supply current, AL8400 output current and the pass transistor

across all input voltage variations.

An alternative way of operating the AL8400 from rails greater than 18V is to take its power supply from the LED chain itself.

Figure 11 High Voltage Operation Tapping V

CC

from the LED String

When the supply voltage for the AL8400 is derived from the LED string, care has to be taken in dimensioning the resistor R

B

. The current spilled

from the LED chain can reduce the accuracy of the system and brightness matching between the LED.

AL8400/ AL8400Q

Document number: DS35115 Rev. 4 - 2

12 of 13

www.diodes.com

August 2012

AL8400 /

A

L8400Q

Ordering Information

Part Number Package Code Packaging

7” Tape and Reel

Automotive Grade

Quantity Part Number Suffix

AL8400QSE-7 SE SOT353 3000/Tape & Reel -7 Y (Note 5)

AL8400SE-7 SE SOT353 3000/Tape & Reel -7 -

Note: 5. Qualified to AEC-Q100 Grade 1.

Marking Information

(1) SOT353

1 2 3

5

7

4

XX

Y

W

X

( Top View )

XX

: Identification code

W

: Week : A~Z : 1~26 week;

X

: A~Z : Green

Y

: Year 0~9

a~z : 27~52 week; z represents

52 and 53 week

Part Number Package Identification Code

AL8400SE-7 SOT353 B4

AL8400QSE-7 SOT353 B4

Package Outline Dimensions (All dimensions in mm.)

Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.

SOT353

Dim Min Max

A 0.10 0.30

B 1.15 1.35

C 2.00 2.20

D 0.65 Typ

F 0.40 0.45

H 1.80 2.20

J 0 0.10

K 0.90 1.00

L 0.25 0.40

M 0.10 0.22

α

0° 8°

All Dimensions in mm

A

M

J

L

D

B C

H

K

F

STTH3002G

STTH3002G

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