LT3013
16
3013fe
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.
P
EFF
= 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 3Ω 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 fl ux left after
insufficient 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 10µA. Consider junction temperature
increase due to power dissipation in both the junction and
nearby components to ensure maximum specifi cations 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, LT3013MP) 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.
