LT3023 LINER [Linear Technology], LT3023 Datasheet - Page 9

• Manufacturer Part Number: LT3023
• Description: Dual 100mA, Low Dropout, Low Noise, Micropower Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
The LT3023 is a dual 100mA low dropout regulator with
micropower quiescent current and shutdown. The device
is capable of supplying 100mA per channel at a dropout
voltage of 300mV. Output voltage noise can be lowered to
20 V
addition of a 0.01 F reference bypass capacitor. Addition-
ally, the reference bypass capacitor will improve transient
response of the regulator, lowering the settling time for
transient load conditions. The low operating quiescent
current (20 A per channel) drops to less than 1 A in
shutdown. In addition to the low quiescent current, the
LT3023 regulator 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 LT3023 acts like it has a
diode in series with its output and prevents reverse current
flow. Additionally, in dual supply applications where the
regulator load isreturned to a negative supply, the output
can be pulled below ground by as much as 20V and still
allow the device to start and operate.
Adjustable Operation
The LT3023 has an output voltage range of 1.22V to 20V.
The output voltage is set by the ratio of two external resis-
tors as shown in Figure 1. The device servos the output to
maintain the corresponding ADJ1/ADJ2 pin voltage at
1.22V referenced to ground. The current in R1 is then equal
to 1.22V/R1 and the current in R2 is the current in R1 plus
the ADJ1/ADJ2 pin bias current. The ADJ1/ADJ2 pin bias
current, 30nA at 25 C, flows through R2 into the ADJ1/ADJ2
pin. The output voltage can be calculated using the formula
in Figure 1. The value of R1 should be no greater than 250k
to minimize errors in the output voltage caused by the ADJ1/
ADJ2 pin bias current. Note that in shutdown the output is
turned off and the divider current will be zero. Curves of
ADJ1/ADJ2 Pin Voltage vs Temperature and ADJ1/ADJ2 Pin
Bias Current vs Temperature appear in the Typical Perfor-
mance Characteristics.
RMS
over a 10Hz to 100kHz bandwidth with the
U
U
W
U
The device is tested and specified with the ADJ1/ADJ2 pin
tied to the corresponding OUT1/OUT2 pin for an output
voltage of 1.22V. Specifications for output voltages greater
than 1.22V will be proportional to the ratio of the desired
output voltage to 1.22V: V
regulation for an output current change of 1mA to 100mA
is –1mV typical at V
regulation is:
Bypass Capacitance and Low Noise Performance
The LT3023 regulator may be used with the addition of a
bypass capacitor from V
BYP2 pin to lower output voltage noise. A good quality low
leakage capacitor is recommended. This capacitor will
bypass the reference of the regulator, providing a low fre-
quency noise pole. The noise pole provided by this bypass
capacitor will lower the output voltage noise to as low as
20 V
Using a bypass capacitor has the added benefit of improv-
ing transient response. With no bypass capacitor and a
10 F output capacitor, a 10mA to 100mA load step will
settle to within 1% of its final value in less than 100 s. With
the addition of a 0.01 F bypass capacitor, the output will
stay within 1% for a 10mA to 100mA load step (see Tran-
sient Reponse in Typical Performance Characteristics sec-
tion). However, regulator start-up time is inversely pro-
portional to the size of the bypass capacitor, slowing to
15ms with a 0.01 F bypass capacitor and 10 F output
capacitor.
(12V/1.22V)(–1mV) = – 9.8mV
V
IN
RMS
IN
with the addition of a 0.01 F bypass capacitor.
OUT1/OUT2
LT3023
ADJ1/ADJ2
GND
Figure 1. Adjustable Operation
R2
R1
OUT
3023 F01
+
OUT
= 1.22V. At V
OUT
V
OUT
to the corresponding BYP1/
/1.22V. For example, load
I
OUTPUT RANGE = 1.22V TO 20V
V
V
ADJ
OUT
ADJ
30
1 22
1 22
nA
OUT
V
V
AT 25 C
1
= 12V, load
R
LT3023
R
2
1
I
ADJ
9
3023f
R
2