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TPS72115

1.8 V

1.5 V

Boost Converter

3.3 V

1.8 V – 3 V

DSP or

Controller

Two AAA

Batteries

EXTERNAL CAPACITOR REQUIREMENTS

POWER DISSIPATION AND JUNCTION TEMPERATURE

P

D(max) +

T

J

max * TA

R

q

JA

(1)

P

D +

V

I *

V

O

I

O

(2)

REGULATOR PROTECTION

TPS72118-EP

SGDS037A – OCTOBER 2007 – REVISED DECEMBER 2007

Figure 18. Dual Supply Application Circuit

A 0.1-

µF ceramic bypass capacitor is required on both the input and output for stability. Larger capacitors

improve transient response, noise rejection, and ripple rejection. A higher value electrolytic input capacitor may

be necessary if large, fast rise time load transient are anticipated, and/or there is significant input resistance from

the device to the input power supply.

Specified regulator operation is ensured to a junction temperature of 125

°C; the maximum junction temperature

allowable without damaging the device is 150

°C. This restriction limits the power dissipation the regulator can

handle in any given application. To ensure the junction temperature is within acceptable limits, calculate the

The maximum power dissipation limit is determined using Equation 1 :

Where:

• T

• T

The regulator dissipation is calculated using Equation 2:

Power dissipation resulting from quiescent current is negligible.

The TPS72118 pass element has a built-in back diode that safely conducts reverse current when the input

voltage drops below the output voltage (for example, during power down). Current is conducted from the output

to the input and is not internally limited. If extended reverse voltage is anticipated, external limiting might be

appropriate.

The TPS72118 also features internal current limiting and thermal protection. During normal operation, the

TPS72118 limits output current to approximately 350 mA. When current limiting engages, the output voltage

scales back linearly until the overcurrent condition ends. While current limiting is designed to prevent gross

device failure, care should be taken not to exceed the power dissipation ratings of the package. If the

temperature of the device exceeds 170

°C, thermal-protection circuitry shuts it down. Once the device has cooled

down to below 150

°C, regulator operation resumes.

8

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Product Folder Link(s): TPS72118-EP