TC1017 Ver la hoja de datos (PDF) - Microchip Technology

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Fabricante

TC1017

150 mA, Tiny CMOS LDO With Shutdown

Microchip Technology 

160

140

120

100

80

60

40

20

0

-40

VIN - VOUT = 1V

-15 10 35 60 85 110

Ambient Temperature (°C)

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 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:

PD = (VIN – VOUT) × ILOAD + VIN × IGND

The VIN x IGND term is typically very small when

compared to the (VIN-VOUT) x ILOAD term, simplifying the

power dissipation within the LDO to be:

EQUATION:

PD = (VIN – VOUT) × ILOAD

To determine the maximum power dissipation

capability, the following equation is used:

TC1017

EQUATION:

PDMAX

=

(---T---J--_--M-----A---X-----–-----T---A---_---M----A---X----)-

RθJA

Where:

TJ_MAX = the maximum junction

temperature allowed

TA_MAX = the maximum ambient

temperature

RθJA = the thermal resistance from

junction to air

Given the following example:

Find:

VIN =

VOUT =

ILOAD =

TA =

3.0V to 4.1V

2.85V ±2.5%

120 mA (output current)

+85°C (max. desired ambient)

1. Internal power dissipation:

PDMA X = (VIN_MAX – VOUT_MIN ) × ILOAD

= (4.1V – 2.85 × (0.975)) × 120mA

= 158.5mW

2. Maximum allowable ambient temperature:

TA_MAX = TJ_MAX – PDMAX × RθJA

= (125°C – 158.5mW × 255°C/W)

= (125°C – 40.5°C)

= 84.5°C

3. Maximum allowable power dissipation at

desired ambient:

PD

=

T----J--_---M----A--X-----–----T----A-

RθJA

= -1--2----5---°--C------–-----8---5---°---C--

255°C/W

= 157mW

In this example, the TC1017 dissipates approximately

158.5 mWatts 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 and

typical maximum current versus ambient temperature

with a one volt input voltage to output voltage

differential, respectively.

 2003 Microchip Technology Inc.

DS21813B-page 13

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