A6850KLTR-T(2011) 데이터 시트보기 (PDF) - Allegro MicroSystems

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A6850KLTR-T
(Rev.:2011)

Dual Channel Switch Interface IC

Allegro MicroSystems 

A6850

Dual Channel Switch Interface IC

TJ can be estimated by calculating the power dissipation (PD) of

the A6850. To calculate PD:

PD = VIN IINQ

(6)

– VOUTPUT1 IOUTPUT1 – VOUTPUT2 IOUTPUT2

– VSENSE1 ISENSE1 – VSENSE2 ISENSE2 .

PD = VIN IINQ

(7)

+ (VIN – VOUTPUT1 ) IOUTPUT1

+ (VIN – VOUTPUT2 ) IOUTPUT2

+ (VIN – VSENSE1) ISENSE1

+ (VIN – VSENSE2) ISENSE2 .

When IOUTPUTx × RDS(on) < approximately 700 mV, then:

(VIN – VOUTPUTx ) = IOUTPUTx × RDS(on) .

When IOUTPUTx × RDS(on) > approximately 700 mV, then:

IOUTPUTx = IOUTPUT (max) ,

and VOUTPUTx is set by the loading on the OUTPUTx pin.

The temperature rise of the A6850 can be calculated by multiply-

ing PD and the thermal resistance from junction to ambient, RθJA .

The formula for temperature rise, ΔT, is:

Example: Calculating the power dissipation and temperature rise,

given:

TA = 25°C ,

VIN = 5 V ,

IINQ = 5 mA ,

IOUTPUT1 = IOUTPUT2 = 15 mA ,

ISENSEx = IOUTPUTx /10 = 1.5 mA ,

RSENSE1 = RSENSE2 = 2 kΩ , and

IOUTPUTx × RDS(on) = 15 × 35 = 525 mV = VIN – VOUTPUTx .

Then:

PD = 5 V × 5 mA

+ 0.525 V×15 mA+[5 V – (1.5 mA×2 kΩ)]×1.5 mA

+ 0.525 V×15 mA+[5 V – (1.5 mA×2 kΩ)]×1.5 mA

= 46.75 mW .

Substituting in equation 8:

ΔT = 46.75 mW × 140 °C/W = 6.5°C .

 ΔT = PD × RθJA .

(8)

The RθJA for an 8-pin SOIC (Allegro L package) on a one-layer

board with minimum copper area is 140 °C/W. (More thermal

data is available on the Allegro MicroSystems website.)

The total junction temperature can be calculated by:

Substituting in equation 9:

TJ = 25°C + 6.5°C = 31.5°C .

TJ = TA + ΔT ,

(9)

where TA is the ambient air temperature.

Allegro MicroSystems, Inc.

7

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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