LT3023
9
3023fa
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 20μV
RMS
over a 10Hz to 100kHz bandwidth with the
addition of a 0.01μF 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 (20μA per channel) drops to less than 1μA 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
fl ow. 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, fl ows through R2 into the
ADJ1/ADJ2 pin. The output voltage can be calculated us-
ing 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 Performance Characteristics.
The device is tested and specifi ed with the ADJ1/ADJ2
pin tied to the corresponding OUT1/OUT2 pin for an out-
put voltage of 1.22V. Specifi cations for output voltages
greater than 1.22V will be proportional to the ratio of the
desired output voltage to 1.22V: V
OUT
/1.22V. For example,
load regulation for an output current change of 1mA to
100mA is –1mV typical at V
OUT
= 1.22V. At V
OUT
= 12V,
load regulation is:
(12V/1.22V)(–1mV) = –9.8mV
Bypass Capacitance and Low Noise Performance
The LT3023 regulator may be used with the addition of a
bypass capacitor from V
OUT
to the corresponding BYP1/
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 frequency noise pole. The noise pole provided by this
bypass capacitor will lower the output voltage noise to
as low as 20μV
RMS
with the addition of a 0.01μF bypass
capacitor. Using a bypass capacitor has the added benefi t
of improving transient response. With no bypass capacitor
and a 10μF output capacitor, a 10mA to 100mA load step
will settle to within 1% of its fi nal value in less than 100μs.
With the addition of a 0.01μF bypass capacitor, the output
will stay within 1% for a 10mA to 100mA load step (see
Transient Reponse in Typical Performance Characteristics
section). However, regulator start-up time is proportional
to the size of the bypass capacitor, slowing to 15ms with
a 0.01μF bypass capacitor and 10μF output capacitor.
Figure 1. Adjustable Operation
IN
3023 F01
R2
LT3023
OUT1/OUT2
V
IN
V
OUT
ADJ1/ADJ2
GND
R1
+
VV
R
R
IR
VV
InA
OUT ADJ
ADJ
ADJ
=+
⎛
⎝
⎜
⎞
⎠
⎟
+
()()
=
=°
122 1
2
1
2
122
30
.
.
AT 25 C
OUTPUT RANGE = 1.22V TO 20V
APPLICATIONS INFORMATION
