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LT3032

3032f

APPLICATIONS INFORMATION

Calculating Junction Temperature

Example: Given a positive output voltage of 3.3V, a positive

input voltage of 4V to 6V, output current range from 10mA

to 150mA, negative output voltage of –3.3V, negative input

voltage of –5V to –6V, a negative output current of –100mA,

and a maximum ambient temperature of 50°C, what will

the maximum junction temperature be for a 2500mm2

board with topside copper of 1000mm2?

The power in each side equals:

PSIDE = (VIN(MAX) – VOUT)(IOUT(MAX))+(VIN(MAX)•IGND)

where,

IOUTP(MAX) = 150mA

VINP(MAX) = 6V

IGND at (IOUTP = 150mA, VINP = 6V) = 3.7mA

IOUTN(MAX) = –100mA

VINN(MAX) = –6V

IGND at (IOUTN = –100mA, VINN = –6V) = –1.5mA

The total power equals:

PTOTAL = PPOSITIVE + PNEGATIVE

So,

PPOSITIVE = 150mA(6V – 3.3V) + 3.7mA(6V) = 0.43W

PNEGATIVE = –100mA(–6V+3.3V)–1.5mA(–6V) =

0.28W

PTOTAL = 0.43W + 0.28W = 0.71W

Junction Temperature equals:

TJ = TA + PTOTAL • θJA (using tables)

TJ = 50°C + 0.71W • 33°C/W = 73.4°C

In this case, the junction temperature is below the maximum

rating, ensuring reliable operation.

Protection Features

The LT3032 incorporates several protection features

that make it ideal for use in battery-powered circuits. In

addition to the normal protection features associated with

monolithic regulators, such as current limiting and thermal

limiting, the LT3032 is protected against reverse input

voltages and reverse output voltages on both channels.

Current limit protection and thermal overload protection

protect the device against current overload conditions at

the outputs of the part. For normal operation, the junction

temperature should not be allowed to exceed 125°C.

The positive input of the LT3032 withstands 20V reverse

voltage. The negative input also withstands reverse

voltage, but the negative input may not be more than 0.5V

(one VBE) higher than the OUTN and SHDNN pins. This

provides protection against batteries that are plugged in

backwards.

The outputs of the LT3032 can be pulled to opposing

voltages without damaging the part. The outputs may be

pulled to the opposing polarity with a load that is common

mode between the two and one regulator starts before the

other; in this condition, it does not matter which regulator

started ﬁrst. Both sides are capable of having the output

pulled to the opposing polarity and both will still start

and operate.

If an input is left open circuit or grounded, the corre-

sponding output can be pulled to its opposing polarity by

as much as 20V. The output will act like an open circuit;

no current will ﬂow into or out of the pin. If the input is

short-circuit current and will protect itself by thermal

limiting. In this case, grounding the respective SHDNP/

SHDNN pin will turn off that side of the LT3032 and stop

the output from sourcing current.

The ADJP pin can be pulled above or below ground by

±7V without damage to the device. If the input is left open

circuit or grounded, the ADJP pin acts like an open circuit

when pulled below ground and like a large resistor (typically

100k) in series with a diode when pulled above ground.

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