TC1017 datasheet(13/22 Pages) MICROCHIP

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DS21813D-page 13

TC1017

FIGURE 5-2:

Maximum Current vs.

Ambient Temperature (SC-70 package).

5.3

Power Dissipation: SOT-23

The TC1017 is also available in a SOT-23 package for

improved thermal performance. The thermal resistance

for the SOT-23 package is approximately 255°C/W

when the copper area used in the printed circuit board

layout is similar to the JEDEC J51-7 low thermal

conductivity standard or semi-G42-88 standard. For

applications with a larger or thicker copper area, the

thermal resistance can be lowered. See AN792, “A

Method to Determine How Much Power a SOT-23 Can

Dissipate in an Application”, DS00792, for a method to

determine the thermal resistance for a particular

application.

The TC1017 power dissipation capability is dependant

upon several variables: input voltage, output voltage,

load current, ambient temperature and maximum

junction temperature. The absolute maximum steady-

state junction temperature is rated at +125°C. The

power dissipation within the device is equal to:

EQUATION 5-4:

The V

x I

GND

term is typically very small when

compared to the (V

IN–VOUT) x ILOAD term, simplifying the

power dissipation within the LDO to be:

EQUATION 5-5:

determine

the

maximum

power

dissipation

capability, the following equation is used:

EQUATION 5-6:

Given the following example:

Find:

Internal power dissipation:

Maximum allowable ambient temperature:

Maximum

allowable

power

dissipation

desired ambient:

In this example, the TC1017 dissipates approximately

158.5 mW and the junction temperature is raised

40.5°C over the ambient. The absolute maximum

power dissipation is 157 mW when given a maximum

ambient temperature of +85°C.

Input voltage, output voltage or load current limits can

also be determined by substituting known values in the

power dissipation equations.

Figure 5-3 and Figure 5-4 depict typical maximum

power dissipation versus ambient temperature, as well

as typical maximum current versus ambient tempera-

ture with a 1V input voltage to output voltage

differential, respectively.

100

120

140

160

-40

-15

110

Ambient Temperature (°C)

IN - VOUT = 1V

OUT

–

() I

LOAD

GN D

OUT

–

() I

LOAD

VIN =

3.0V to 4.1V

VOUT =

2.85V ±2.5%

ILOAD =

120 mA (output current)

TA =

+85°C (max. desired ambient)

DMAX

J_MAX

A_MAX

–

()

----------------------------------------------

Where:

TJ_MAX = the maximum junction

temperature allowed

TA_MAX = the maximum ambient

temperature

θJA

= the thermal resistance from

junction to air

DMAX

IN_MAX

OUT_MIN

–

() I

LOAD

4.1V

2.85

0.975

()

–

() 120mA

158.5mW

A_MAX

J_MAX

–

DMAX

125

°C 158.5mW 255°C/W

–

()

84.5

°C

125

°C40.5°C

–

()

J_MAX

–

------------------------------

157mW

125

°C85°C

–

255

°C/W

-----------------------------------

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