Datasheet

LT3029
12
3029fb
For more information www.linear.com/LT3029
The LT3029 is a dual 500mA/500mA low dropout regulator
with independent inputs, micropower quiescent current
and shutdown. The device supplies up to 500mA from each
channel’s output at a typical dropout voltage of 300mV.
The two regulators share a common GND pin and are
thermally coupled. However, the two inputs and outputs of
the LT3029 operate independently. Each channel can be
shut down independently, but a thermal shutdown fault
on either channel shuts off the output on both channels.
The addition of a 10nF reference bypass capacitor lowers
output voltage noise to 20µV
RMS
over a 10Hz to 100kHz
bandwidth. Additionally, the reference bypass capacitor
improves transient response of the regulator, lowering
the settling time for transient load conditions. The low
operating quiescent current (55µA per channel) drops to
less than 1µA in shutdown. In addition to the low quies
-
cent current, the LT3029 regulator incorporates several
protection features that make it ideal for use in battery-
powered systems. Most importantly, the device protects
itself against reverse input voltages. Current limiting with
foldback necessitates a minimum load current of 20µA
for input/output voltage differentials of more than 10V to
keep the output regulated.
Adjustable Operation
Each of the LT3029’s channels has an output voltage range
of 1.215V to 19.5V. Figure 1 illustrates that output voltage
is set by the ratio of two external resistors. The device
regulates the output to maintain the corresponding ADJ
pin voltage at 1.215V referenced to ground. R1’s current
equals 1.215V/R1. R2’s current equals R1’s current plus
the ADJ pin bias current. The ADJ pin bias current, 30nA at
25°C, flows through R2 into the ADJ pin. Use the formula
in Figure 1 to calculate output voltage. Linear Technol
-
ogy recommends that the value of R1 be less than 243k
to minimize errors in the output voltage due to the ADJ
pin bias current. In shutdown, the output turns off and
the divider current is zero. Cur
ves of ADJ Pin V
oltage vs
Temperature and ADJ Pin Bias Current vs Temperature
appear in the Typical Performance Characteristics section.
applicaTions inForMaTion
Figure 1. Adjustable Operation
IN1/IN2
3029 F01
C
LT3029
OUT1/OUT2
V
IN
V
OUT
ADJ1/ADJ2
GND
R1
R2
Linear Technology tests and specifies each LT3029 channel
with its ADJ pin tied to the corresponding OUT pin for a
1.215V output voltage. Specifications for output voltages
greater than 1.215V are proportional to the ratio of desired
output voltage to 1.215V:
V
OUT
1.215V
For example, load regulation on either output for an output
current change of 1mA to 500mA is typically –2.5mV at
V
OUT
= 1.215V. At V
OUT
= 2.5V, load regulation is:
2.5V
1.215V
• (−2.5mV) = − 5.14mV
Table 1 shows 1% resistor divider values for some com-
mon output voltages with a resistor divider current of
approximately 5µA.
Table 1. Output Voltage Resistor Divider Values
V
OUT
(V)
R1
(k)
R2
(k)
1.5 237 54.9
1.8 237 113
2.5 243 255
3 232 340
3.3 210 357
5 200 619
V
OUT
= 1.215V 1+
R2
R1






+ I
ADJ
( )
R2
( )
V
ADJ
= 1.215V
I
ADJ
= 30nA AT 25°C
OUTPUT RANGE = 1.215V TO 19.5V