LT3010 LINER [Linear Technology], LT3010 Datasheet - Page 8

• Manufacturer Part Number: LT3010
• Description: 50mA, 3V to 80V Low Dropout Micropower Linear Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LT3010/LT3010-5
The LT3010 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 (30 A)
drops to 1 A in shutdown. In addition to the low quiescent
current, the LT3010 incorporates several protection fea-
tures 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 LT3010 acts
like it has a diode in series with its output and prevents
reverse current flow.
Adjustable Operation
The adjustable version of the LT3010 has an output
voltage range of 1.275V to 60V. The output voltage is set
by the ratio of two external resistors as shown in Figure 2.
The device servos the output to maintain the voltage at
the adjust pin at 1.275V referenced to ground. The
current in R1 is then equal to 1.275V/R1 and the current
in R2 is the current in R1 plus the ADJ pin bias current.
The ADJ pin bias current, 50nA at 25 C, flows through R2
into the ADJ pin. The output voltage can be calculated
using the formula in Figure 2. 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 shut-
down the output is turned off and the divider current will
be zero.
8
U
U
W
V
IN
Figure 2. Adjustable Operation
V
V
I
OUTPUT RANGE = 1.275V TO 60V
U
ADJ
OUT
ADJ
IN
= 50nA AT 25 C
LT3010
= 1.275V
= 1.275V
GND
OUT
ADJ
1 +
R2
R1
R2
R1
A small capacitor (C1) placed in parallel with the top
resistor (R2) of the output divider is necessary for stability
and transient performance of the adjustable LT3010. The
impedance of C1 at 10kHz should be less than the value of
R1.
The adjustable device is tested and specified with the ADJ
pin tied to the OUT pin and a 5 A DC load (unless otherwise
specified) for an output voltage of 1.275V. Specifications
for output voltages greater than 1.275V will be propor-
tional to the ratio of the desired output voltage to 1.275V;
(V
output current change of 1mA to 50mA is –10mV typical
at V
Output Capacitance and Transient Response
The LT3010 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 1 F with an ESR of 3
recommended to prevent oscillations. The LT3010 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 LT3010, will increase the
effective output capacitor value.
+ (I
OUT
ADJ
(12V/1.275V) • (–10mV) = –94mV
OUT
)(R2)
/1.275V). For example, load regulation for an
C1
= 1.275V. At V
+
3010 F02
V
OUT
OUT
= 12V, load regulation is:
or less is
3010f