LT3050 Series
17
3050fa
The LT3050 is a micropower, low noise and low dropout
voltage, 100mA linear regulator with micropower shutdown,
programmable current limit, and diagnostic functions. The
device supplies up to 100mA at a typical dropout voltage
of 340mV and operates over a 2.2V to 45V input range.
A single external capacitor can provide low noise reference
performance and output soft-start functionality. For
example, connecting a 10nF capacitor from the REF/BYP pin
to GND lowers output noise to 30V
RMS
over a 10Hz to
100kHz bandwidth. This capacitor also soft-starts the
reference and prevents output voltage overshoot at turn-on.
The LT3050’s quiescent current is merely 45A but
provides fast transient response with a minimum low ESR
2.2F ceramic output capacitor. In shutdown, quiescent
current is less than 1A and the reference soft-start
capacitor is reset.
The LT3050 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 LT3050 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 LT3050 acts like it has a diode in series with its output
and prevents reverse current fl ow.
Adjustable Operation
The adjustable LT3050 has an output voltage range of
0.6V to 44.5V. The output voltage is set by the ratio of
two external resistors, as shown in Figure 1. The device
servos the output to maintain the ADJ pin voltage at 0.6V
APPLICATIONS INFORMATION
Figure 1. Adjustable Operation
referenced to ground. The current in R1 is then equal to
0.6V/R1, and the current in R2 is the current in R1 minus
the ADJ pin bias current.
V
IN
V
OUT
IN OUT
LT3050
SHDN ADJ
GND
3050 F01
R2
R1
V
OUT
= 0.6V 1+
R2
R1
–I
ADJ
()
•R2
V
ADJ
= 0.6V
I
ADJ
= 16nA at 25°C
OUTPUT RANGE = 0.6V to 44.5V
The ADJ pin bias current, 16nA at 25°C, fl ows from the
ADJ pin through R1 to GND. Calculate the output voltage
using the formula in Figure 1. The value of R1 should be
no greater than 124k to provide a minimum 5A load
current so that output voltage errors, caused by the ADJ
pin bias current, are minimized. Note that in shutdown,
the output is turned off and the divider current is zero.
Curves of ADJ Pin Voltage vs Temperature and ADJ Pin Bias
Current vs Temperature appear in the Typical Performance
Characteristics Section.
The LT3050 is tested and specifi ed with the ADJ pin tied
to the OUT pin, yielding V
OUT
= 0.6V. Specifi cations for
output voltages greater than 0.6V are proportional to the
ratio of the desired output voltage to 0.6V: V
OUT
/0.6V. For
example, load regulation for an output current change
of 1mA to 100mA is –0.2mV (typical) at V
OUT
= 0.6V.
at V
OUT
= 12V, load regulation is:
12
06
02 4
V
V
mV mV
.
–. –•
()
=
