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LT3013

3013fc

APPLICATIONS INFORMATION

Operation at the different power levels is as follows:

76% operation at P1, 19% for P2, 4% for P3, and

1% for P4.

PEFF = 76%(0.23W) + 19%(8.98W) + 4%(0.35W)

+ 1%(13.98W) = 2.03W

With a thermal resistance in the range of 40°C/W to

62°C/W, this translates to a junction temperature rise

above ambient of 81°C to 125°C.

High Temperature Operation

Care must be taken when designing LT3013 applications to

operate at high ambient temperatures. The LT3013 works

at elevated temperatures but erratic operation can occur

due to unforeseen variations in external components. Some

tantalum capacitors are available for high temperature

operation, but ESR is often several ohms; capacitor ESR

above 3

Ω is unsuitable for use with the LT3013. Ceramic

capacitor manufacturers (Murata, AVX, TDK, and Vishay

Vitramon at this writing) now offer ceramic capacitors that

are rated to 150°C using an X8R dielectric. Device instability

will occur if output capacitor value and ESR are outside

design limits at elevated temperature and operating DC

voltage bias (see information on capacitor characteristics

under Output Capacitance and Transient Response). Check

each passive component for absolute value and voltage

ratings over the operating temperature range.

Leakages in capacitors or from solder ﬂux left after insuf-

ﬁcient board cleaning adversely affects low quiescent

current operation. The output voltage resistor divider

should use a maximum bottom resistor value of 124k to

compensate for high temperature leakage, setting divider

current to 10

μA. Consider junction temperature increase

due to power dissipation in both the junction and nearby

components to ensure maximum speciﬁcations are not

violated for the device or external components.

Protection Features

The LT3013 incorporates several protection features which

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

dition to the normal protection features associated with

monolithic regulators, such as current limiting and thermal

limiting, the device is protected against reverse-input volt-

ages, and reverse voltages from output to input.

Current limit protection and thermal overload protection

are intended to protect the device against current overload

conditions at the output of the device. For normal opera-

tion, the junction temperature should not exceed 125°C

(LT3013E) or 140°C (LT3013HFE).

Like many IC power regulators, the LT3013 has safe oper-

ating area protection. The safe area protection decreases

the current limit as input voltage increases and keeps

the power transistor inside a safe operating region for

all values of input voltage. The protection is designed to

provide some output current at all values of input voltage

up to the device breakdown. The SOA protection circuitry

for the LT3013 uses a current generated when the input

voltage exceeds 25V to decrease current limit. This cur-

rent shows up as additional quiescent current for input

voltages above 25V. This increase in quiescent current

occurs both in normal operation and in shutdown (see

curve of Quiescent Current in the Typical Performance

Characteristics).

The input of the device will withstand reverse voltages of

80V. No negative voltage will appear at the output. The

device will protect both itself and the load. This provides

protection against batteries which can be plugged in

backward.

The ADJ pin of the device can be pulled above or below

ground by as much as 7V without damaging the device.

If the input is left open circuit or grounded, the ADJ pin

will act like an open circuit when pulled below ground,

and like a large resistor (typically 100k) in series with a

diode when pulled above ground. If the input is powered

by a voltage source, pulling the ADJ pin below the refer-

ence voltage will cause the device to current limit. This

will cause the output to go to a unregulated high voltage.

Pulling the ADJ pin above the reference voltage will turn

off all output current.

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