LT3071EUFD LINER [Linear Technology], LT3071EUFD Datasheet - Page 16

• Manufacturer Part Number: LT3071EUFD
• Description: 5A, Low Noise, Programmable Output, 85mV Dropout Linear Regulator with Analog Margining
• Manufacturer: LINER [Linear Technology]

LT3071
ApplicAtions inFormAtion
The REF/BYP pin must not be DC loaded by anything except
for applications that parallel other LT3071 regulators for
higher output currents. Consult the Applications Section
on Paralleling for further details.
Output Voltage Margining
The LT3071’s analog margining pin, MARGA, provides a
continuous output voltage adjustment range of ±10%. It
margins V
voltage up and down. The MARGA pin’s typical input
impedance is 190kΩ between MARGA and the internal
V
0% to 10% of adjustment. Driving MARGA with 600mV to
0V provides 0% to –10% of adjustment. If unused, allow
MARGA to float or bypass this pin with a 1nF capacitor
to GND. Note that the analog margining function does not
adjust the PWRGD threshold. Therefore, negative analog
margining may trip the PWRGD comparator and toggle
the PWRGD flag.
Enable Function—Turning On and Off
The EN pin enables/disables the output device only. The
LT3071 reference and all support functions remain active
if V
low puts the LT3071 into nap mode. In nap mode, the
reference circuit is active, but the output is disabled and
quiescent current decreases.
Drive the EN pin with either a digital logic port or an open-
collector NPN or an open-drain NMOS terminated with
a pull-up resistor to V
less than 35k to meet the V
unused, connect EN to BIAS.
Input Undervoltage Lockout on BIAS Pin
An internal undervoltage lockout (UVLO) comparator
monitors the BIAS supply voltage. If V
the UVLO threshold, all functions shut down, the pass
transistor is gated off and output current falls to zero. The
typical BIAS pin UVLO threshold is 1.55V on the rising
edge of V
of hysteresis on the falling edge of V

REF
BIAS
node. Driving MARGA with 600mV to 1.2V provides
is above its UVLO threshold. Pulling the EN pin
BIAS
OUT
. The UVLO circuit incorporates about 150mV
by adjusting the internal 600mV reference
BIAS
. The pull-up resistor must be
IH
condition of the EN pin. If
BIAS
BIAS
.
drops below
High Efficiency Linear Regulator—Input-to-Output
Voltage Control
The VIOC (voltage input-to-output control) pin is a function
to control a switching regulator and facilitate a design solu-
tion that maximizes system efficiency at high load currents
and still provides low dropout voltage performance.
The VIOC pin is the output of an integrated transcon-
ductance amplifier that sources and sinks about 250µA
of current. It typically regulates the output of most LTC
switching regulators or LTM
current from the ITH compensation node. The VIOC function
controls a buck regulator powering the LT3071’s input by
maintaining the LT3071’s input voltage to V
This 300mV V
provide fast transient response and good high frequency
PSRR while minimizing power dissipation and maximizing
efficiency. For example, 1.5V to 1.2V conversion and 1.3V
to 1V conversion yield 1.5W maximum power dissipation
at 5A full output current.
Figure 2 depicts that the switcher’s feedback resistor net-
work sets the maximum switching regulator output voltage
if the linear regulator is disabled. However, once the LT3071
is enabled, the VIOC feedback loop decreases the switching
regulator output voltage back to V
Using the VIOC function creates a feedback loop between
the LT3071 and the switching regulator. As such, the feed-
back loop must be frequency compensated for stability.
Fortunately, the connection of VIOC to many LTC switching
regulator ITH pins represents a high impedance charac-
teristic which is the optimum circuit node to frequency
compensate the feedback loop. Figure 2 illustrates the
typical frequency compensation network used at the VIOC
node to GND.
The VIOC amplifier characteristics are:
g
If the VIOC function is not used, terminate the VIOC
pin to GND with a small capacitor (1000pF) to prevent
oscillations.
m
= 3.2mS, I
IN
OUT
-V
OUT
= ±250µA, BW = 10MHz.
differential voltage is chosen to
®
power modules, by sinking
OUT
+ 300mV.
OUT
+ 300mV.
3071f
®