LT3060_15 Datasheet, PDF (16/26 Pages) Linear Technology – 45V VIN, Micropower, Low Noise, 100mA Low Dropout, Linear Regulator

LT3060 Series
Applications Information
The LT3060 series are micropower, low noise, low drop-
out voltage, 100mA linear regulators with shutdown. The
devices supply up to 100mA at a typical dropout voltage
of 300mV and operate over a 1.6V to 45V input range.
A single external capacitor provides programmable low
noise reference performance and output soft-start func-
tionality. For example, connecting a 10nF capacitor from
the REF/BYP pin to GND lowers output noise to 30µV_RMS
over a 10Hz to 100kHz bandwidth. This capacitor also
soft-starts the reference and prevents output voltage
overshoot at turn-on.
The LT3060’s quiescent current is merely 40μA for the
adjustable version and 45µA for the fixed voltage versions,
while providing fast transient response with a minimum
low ESR 2.2μF ceramic output capacitor. In shutdown,
quiescent current is less than 1μA and the reference soft-
start capacitor is reset.
The LT3060 regulators optimize stability and transient
response with low ESR, ceramic output capacitors. The
regulators do not require the addition of ESR as is com-
mon with other regulators. The LT3060 adjustable version
typically provides 0.1% line regulation and 0.03% load
regulation. For fixed voltage versions, load regulation is
slightly increased due to 20mΩ of typical resistance in
series with the output. Curves of load regulation appear
in the Typical Performance Characteristics section.
Internal protection circuitry includes reverse-battery pro-
tection, reverse-output protection, reverse-current protec-
tion, current limit with foldback and thermal shutdown.
This “bullet-proof” protection set makes it ideal for use in
battery-powered systems. In battery backup applications
where the output is held up by a backup battery and the
input is pulled to ground, the LT3060 acts like it has a di-
ode in series with its output and prevents reverse current
flow. Additionally, in dual supply applications where the
regulator load is returned to a negative supply, the output
can be pulled below ground by as much as 45V and the
device still starts normally and operates.
Adjustable Operation
The LT3060 adjustable version 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 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.
The ADJ pin bias current, 15nA at 25°C, flows 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 5µA load current
so that errors in the output voltage, 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 Cur-
rent vs Temperature appear in the Typical Performance
Characteristics section.
The adjustable device is tested and specified with the ADJ
pin tied to the OUT pin, yielding V_OUT = 0.6V. Specifications
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:
12V
0.6V
•
(0.2mV)
=
4mV
IN
OUT
V_IN
LT3060
R2
SHDN ADJ
GND REF/BYP
R1
3060 F01
V_OUT
( ) V_OUT
=
0.6V


1+
R2
R1


–
I_ADJ • R2
V_ADJ = 0.6V
I_ADJ = 15nA at 25º C
OUTPUT RANGE = 0.6V to 44.5V
Figure 1. Adjustable Operation
3060fc
16
For more information www.linear.com/LT3060