1
DESCRIPTION
Demonstration circuit 1433 is an adjustable 5A linear
regulator featuring LT3070. LT3070 is a low dropout
voltage, UltraFast
TM
transient response linear regula-
tor. The device supplies up to 5A of
output current
with a typical dropout voltage of 85mV.
A 0.01µF ref-
erence bypass capacitor decreases output voltage
noise to 25µV
RMS
. The LT3070’s high bandwidth
permits the use of low ESR ceramic capacitors.
Output voltage is digitally selectable in 50mV in-
crements over a 0.8V to 1.8V range. A margining
function allows the user to tolerance system output
voltage in increments of ±1%, ±3% or ±5%. To
maintain proper performance and regulation, the
BIAS supply voltage must be higher than the IN
supply voltage. For a given V
OUT
, the BIAS voltage
must satisfy the following conditions:
2.2 ≤ V
BIAS
≤ 3.6V and V
BIAS
≥ (1.25·V
OUT
+1V).
For V
OUT
≤ 0.95V, the minimum bias voltage is lim-
ited to 2.2V.
The IC incorporates a unique tracking function to
control buck regulator powering the LT3070’s in-
put. This tracking function drives the buck regula-
tor to maintain the LT3070’s input voltage to V
OUT
+
300mV, minimizing power dissipation. It has inter-
nal protection includes UVLO, reverse-current pro-
tection, precision current limiting with power fold-
back and thermal shutdown.
The LT3070 regulator is available in a thermally
enhanced 28-lead, 4mm×5mm QFN package.
The LT3070 datasheet gives a complete de-
scription of the part, operation and application
information. The datasheet must be read in con-
junction with this quick start guide for demo cir-
cuit 1433.
Design files for this circuit board are avail-
able. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
UltraFast is a trade mark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Performance Summary (T
A
= 25
o
C)
PARAMETER CONDITION VALUE
Minimum Input Voltage V
OUT
=1.2V, I
OUT
= 5A 1.32V
Maximum Input Voltage 3V
Minimum Bias Voltage V
OUT
=1.2V 2.5V
Maximum Bias Voltage 3.6V
Output Voltage V
OUT
JP1=LOW, JP2=HIGH, JP3=HIGH
JP4=LOW, JP6=FLOAT
1.2V ±1%
Maximum Output Current V
IN
-V
out
< 0.5V 5A
QUICK START PROCEDURE
Demonstration circuit 1433 is easy to set up to
evaluate the performance of the LT3070. Refer
to Figure 1 for proper measurement equipment
setup and follow the procedure below:
5A, Low Noise, Programmable Output,
85mV Dropout Linear Regulator
