LT3055 Datasheet, PDF (15/24 Pages) Linear Dimensions Semiconductor – 500mA, Linear Regulator with Precision Current Limit and Diagnostics

LT3055
OPERATION
The I_MAX pin requires a 22nF decoupling capacitor. If the
external programmable current limit is not needed, the
I_MAX pin must be connected to GND. The I_MAX threshold
is affected by power dissipation in the LT3055; it increases
at a rate of approximately 0.5 percent per watt.
FAULT Pins Operation
The FAULT1 and FAULT2 pins are open-drain high voltage
NMOS digital outputs. The FAULT1 pin asserts during a low
current fault (open circuit). The FAULT2 pin asserts during
a current limit fault (internal or externally programmed).
Both FAULT1 and FAULT2 assert during thermal shutdown.
There is no internal pull-up on the FAULT pins; an external
pull-up resistor is required. The FAULT pins sink up to
50μA of pull-down current. Off state logic may be as high
as 45V, regardless of the input voltage used.
Table 1. FAULT Pins Truth Table
STATUS
FAULT1
Open Circuit
Low
Current Limit
High
Thermal Shutdown
Low
FAULT2
High
Low
Low
Depending on the I_MIN capacitance, BYP capacitance,
and OUT capacitance, the FAULT pins may assert during
start-up. Consideration should be given to masking the
fault signals during start-up. The FAULT pin circuitry is
inactive (not asserted) during shutdown and when the
OUT pin is pulled above IN pin.
PWRGD Pin Operation
The PWRGD pin is an open-drain high voltage NMOS
digital output. The PWRGD pin deasserts and becomes
high impedance if the output rises above 90% of its
nominal value. If the output falls below 89% of its nominal
value for more than 25μs, the PWRGD pin asserts low.
The PWRGD comparator has 1% hysteresis and 25μs
of deglitching. The PWRGD comparator has a dedicated
reference that does not soft-start when a capacitor is
added to the REF/BYP pin.
Operation in Dropout
There may be some degradation of the current mirror ac-
curacy for output currents less than 50mA when operating
in dropout.
APPLICATIONS INFORMATION
The LT3055 is a micropower, low noise and low dropout volt-
age, 500mA linear regulator with micropower shutdown,
programmable current limit, and diagnostic functions. The
device supplies up to 500mA at a typical dropout voltage
of 350mV and operates over a 2.2V to 45V input range.
A single external capacitor provides low noise reference
performance and output soft-start functionality. For ex-
ample, connecting a 10nF capacitor from the REF/BYP
pin to GND lowers output noise to 25μV_RMS over a 10Hz
to 100kHz bandwidth. This capacitor also soft starts the
reference and prevents output voltage overshoot at turn-on.
The LT3055’s quiescent current is merely 65μA but provides
fast transient response with a minimum low ESR 3.3μF
ceramic output capacitor. In shutdown, quiescent current is
less than 1μA and the reference soft-start capacitor is reset.
The LT3055 optimizes stability and transient response
with low ESR, ceramic output capacitors. The regulator
does not require the addition of ESR as is common with
other regulators. The LT3055 typically provides 0.1% line
regulation and 0.1% load regulation. Internal protection
circuitry includes reverse battery protection, reverse output
protection, reverse current protection, current limit with
fold-back and thermal shutdown.
This “bullet-proof” protection set makes it ideal for use
in battery-powered, automotive and industrial systems.
In battery backup applications where the output is held
up by a backup battery and the input is pulled to ground,
the LT3055 acts like it has a diode in series with its output
and prevents reverse current flow.
For more information www.linear.com/LT3055
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