lt3011emse Linear Technology Corporation, lt3011emse Datasheet - Page 9

• Manufacturer Part Number: lt3011emse
• Description: 50ma, 3v To 80v Low Dropout Micropower Linear Regulator With Pwrgd
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
The LT3011 is a 50mA high voltage/low dropout regulator
with micropower quiescent current and shutdown. The
device is capable of supplying 50mA at a dropout voltage of
300mV. The low operating quiescent current (46μA) drops
to 1μA in shutdown. In addition to low quiescent current,
the LT3011 incorporates several protection features which
make it ideal for use in battery-powered systems. The
device is protected against both reverse input and reverse
output voltages. In battery backup applications where the
output can be held up by a backup battery when the input
is pulled to ground, the LT3011 acts like it has a diode in
series with its output and prevents reverse current fl ow.
Adjustable Operation
The LT3011 has an output voltage range of 1.24V to 60V. 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 voltage at the adjust pin at 1.24V referenced to ground.
The current in R1 is then equal to 1.24V/R1 and the current
in R2 is the current in R1 plus the ADJ pin bias current.
The ADJ pin bias current, 30nA at 25°C, fl ows through
R2 into the ADJ pin. The output voltage can be calculated
using the formula in Figure 1. The value of R1 should be
less than 250k to minimize errors in the output voltage
caused by the ADJ pin bias current. Note that in shutdown
the output is turned off and the divider current will be zero.
The adjustable device is tested and specifi ed with the
ADJ pin tied to the OUT pin and a 5μA DC load (unless
otherwise specifi ed) for an output voltage of 1.24V. Speci-
V
V
I
OUTPUT RANGE = 1.24V TO 60V
ADJ
OUT
ADJ
= 30nA AT 25 C
= 1.24V
= V
ADJ
1 +
R2
R1
+ (I
ADJ
)(R2)
Figure 1. Adjustable Operation
V
IN
IN
LT3011
fi cations for output voltages greater than 1.24V will be
proportional to the ratio of the desired output voltage to
1.24V; (V
output current change of 1mA to 50mA is –6mV (typical)
at V
Output Capacitance and Transient Response
The LT3011 is designed to be stable with a wide range
of output capacitors. The ESR of the output capacitor
affects stability, most notably with small capacitors. A
minimum output capacitor of 1μF with an ESR of 3Ω or
less is recommended to prevent oscillations. The LT3011
is a micropower device and output transient response
will be a function of output capacitance. Larger values
of output capacitance decrease the peak deviations and
provide improved transient response for larger load current
changes. Bypass capacitors, used to decouple individual
components powered by the LT3011, will increase the
effective output capacitor value.
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
temperature and applied voltage. The most common
dielectrics used are specifi ed with EIA temperature char-
acteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitances
GND
1 24
OUT
OUT
12
ADJ
.
V
= 1.24V. At V
V
OUT
• –
/1.24V). For example, load regulation for an
R2
R1
6
mV
+
=
OUT
–
58
3011 F01
V
= 12V, load regulation is:
OUT
mV
LT3011
9
3011f