AS1360 datasheet(9/14 Pages) AMSCO

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AS1360

Datasheet - A p p l i c a t i o n I n f o r m a t i o n

9 Application Information

Figure 14. AS1360 - Typical Application Diagram

Power Dissipation

Power dissipation (PD) of the AS1360 is the sum of the power dissipated by the p-channel MOSFET and the quiescent current required to bias

the internal voltage reference and the internal power amplifier, and is calculated as:

PD (P-Channel MOSFET) = (VIN - VOUT)IOUT

(EQ 1)

Internal power dissipation as a result of the bias current for the internal voltage reference and the error amplifier is calculated as:

PD (Bias) = VINIGND

(EQ 2)

Total AS1360 power dissipation is calculated as:

PD(Total) = PD (P-Channel MOSFET) + PD (Bias)

(EQ 3)

The internal quiescent bias current (2 A, typ) is such that the PD(Bias) term of (EQ 3) can be disregarded and the maximum power dissipation

can be estimated using VIN(MAX) and VOUT(MIN) to obtain a maximum voltage differential between VIN and VOUT, and multiplying the maxi-

mum voltage differential by the maximum output current:

PD = (VIN(MAX)VOUT(MIN))IOUT(MAX)

(EQ 4)

Where:

VIN = 3.3 to 4.1V

VOUT = 3.0V ±2%

IOUT = 1 to 100mA

TAMB(MAX) = 55ºC

PMAX = (4.1V - (3.0V x 0.98)) x 100mA = 116.0mW

Junction Temperature

The AS1360 junction temperature (TJ) can be determined by first calculating the thermal resistance from junction temperature-to-ambient tem-

perature.

Note:

Thermal resistance is estimated to be the junction temperature-to-air temperature R

ΦJA, and is approximately 230°C/W or 335ºC/W

(when mounted on 1 square inch of copper). R

ΦJA will vary depending on PCB layout, air-flow and application specific conditions.

The AS1360 junction temperature is determined by calculating the rise in TJ above TAMB, and then adding the increase of TAMB:

TJ = PD(MAX) x R

ΦJA + TAMB

(EQ 5)

From (EQ 5), the value of TJ can be calculated as:

TJ = 116.0mW x 230ºC/W + 55ºC

Therefore:

TJ = 81.68ºC

AS1360

+9V

Alkaline

Battery

GND

VIN

VOUT

COUT

1µF

CIN

1µF

Tantalum Capacitor

VOUT = 3.3V

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