TC1307 datasheet(17/28 Pages) MICROCHIP

17 / 28 page

 2002 Microchip Technology Inc.

DS21702A-page 17

TC1307

5.4.1

P-CHANNEL LINEAR PASS DEVICE

Where:

PLinear = Power dissipated in the LDO P-Channel

linear pass element.

VIN(MAX) = Maximum input voltage (VIN)

VOUT(MAX) = Minimum LDO output Voltage (VOUT)

IOUT(MAX) = Maximum LDO output current

5.4.2

QUIESCENT CURRENT

The quiescent current consumed by the TC1307 has

two components. The quiescent current required to

bias the LDO regulators and the quiescent current

required to bias the voltage detection circuitry. To deter-

mine the power dissipation as a result of the total

device quiescent current both the maximum input volt-

age on the VIN and VDET inputs should be used.

Where:

PQ = Power internal to the LDO as a result of inter-

nal biasing

VIN = Input voltage

IIN = Input current when all load currents = 0 mA

VDET = Detect Input Voltage

IVDET = Voltage detect input pin current

5.4.3

RESET OUTPUT

The power dissipation for the RESET output driver can

be a result of the sinking current or sourcing current

depending on the state of the output.

Where:

PRESET = Power dissipated as a result of the

RESET output.

VOL = RESET low output voltage

ISINK = RESET sink current

The power dissipation internal to the RESET output

due to sourcing current can be calculated by using the

following equation.

Where:

PRESET = Power dissipation as a result of RESET

output while in the high state

VDET = Detect Voltage

VSOURCE = RESET output pin voltage while in the

high state

ISOURCE = Output current being sourced

5.4.4

TOTAL INTERNAL POWER DISSIPATION

The total power dissipated within the TC1307 is the

sum of the power dissipated in each of the four LDOs,

the PQ term and the PRESET term (either sinking or

sourcing). Because of the CMOS construction, the typ-

ical IIN for the TC1307 is 220 µA. When operating at a

maximum of 5V this results is a power dissipation of

1.2 milli-Watts. For most applications this is small com-

pared to the LDO pass device power dissipation and

can be neglected. The PRESET term for a typical 3.2 mA

sinking application will dissipate a maximum of 3.2 mA

x 0.4V or 1.28 milli-Watts. A typical sourcing applica-

tion of 800 µA will have a maximum 1.5V drop from the

VDET voltage will dissipate a maximum of 800 µA x

1.5V or 1.2 milli-Watts. Again for most applications this

is small compared to the LDO pass device power dissi-

pation and can be neglected.

5.4.5

MAXIMUM JUNCTION TEMPERATURE

The operating junction temperature (TJ) specified for

the TC1307 is 125°C. To estimate the internal junction

temperature of the TC1307, the total internal power dis-

sipation (PTOTAL) is multiplied by the thermal resistance

from junction to ambient (

θJA) of the device. The ther-

mal resistance from junction to ambient for the QSOP

16-pin package is estimated at 112.4°C/W. The actual

thermal resistance from junction to air can vary from

application to application for the QSOP16 depending

on board copper area, copper thickness, airflow and

other external environmental factors.

The maximum power dissipation capability for a pack-

age (PD(MAX)) can be calculated given the junction to

air thermal resistance and the maximum ambient tem-

perature (TA(MAX)) for the application. The following

equation can be used to determine the package maxi-

mum internal power dissipation.

PLinear

VIN MAX

() VOUT MIN

()

–

() IOUT MAX

()

VIN IIN

VDET IDET

PRESET

VOL ISINK

PRESET

VDET VSOURCE

–

() I

SOUR CE

PTOTAL

PLinear P

PRESET

TJMAX

()

PTOTAL θJA

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