LT3048 datasheet(12/22 Pages) LINER

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LT3095

3095fa

For more information www.linear.com/LT3095

APPLICATIONS INFORMATION

The LT3095 is an easy-to-use step-up bias generator with

two independent channels supporting loads up to 50mA.

Since the boost converters are monolithic and feature in-

ternal compensation, the LT3095 is easy to configure with

a few external components. The output of each switcher is

post-regulated by a linear regulator to filter output ripple

and provide a precision DC voltage with very low noise for

biasing sensitive circuits and sensors. The output of each

channel is programmed with a single resistor and internal

feedback automatically regulates the output of each boost

converterto2Vabovethecorrespondinglinearregulator’s

output. The filtered outputs are protected by independent

current limit and thermal shutdown.

3095 F01

–

+–

VIN

SW1

BSTOUT1

LDOIN1

GND

SET1

OUT1

10µF

2.2µF

50µA

RSET1

CTRL

VIN

Figure 1. LT3095 Architecture (Single Channel)

Programming the Output Voltage

Figure 1 illustrates the architecture of the LT3095. The

boost converter simply regulates the difference between

LDOIN and OUT – no external feedback configuration is

necessary. The linear regulators have a single-resistor-

programmable reference architecture. An accurate,

temperature-compensated 50µA current flows out of the

SET pin and into an external resistor, RSET, to establish

the reference for the linear regulator output voltage. To

program the output, simply choose the appropriate SET

pin resistor according to Ohm’s law:

RSET =

VOUT

50µA

The SET pin voltage is buffered to the output, so the linear

regulator always operates in unity gain configuration. This

allows optimal loop gain and bandwidth regardless of

output voltage. With this architecture, it is also possible

to drive the set pin externally for a dynamic supply (see

the Typical Applications section below).

TheLT3095step-upregulatortrackstheoutputofthelinear

regulator and maintains 2V typically between LDOIN and

OUT of each channel. This input-to-output voltage control

obviates the need to externally program the boost output

voltage and insures controlled power dissipation in the

linearregulatorpassdevice,evenifthetargetoutputvoltage

is adjusted or programmed dynamically during operation.

Boost Output Capacitor/Linear Regulator Input Capacitor

TheLT3095step-upconvertersareinternallycompensated

and require an output capacitor, which also serves as the

input capacitor for the linear regulator. A value of 10µF is

recommended. Consider capacitance degradation under

bias and temperature conditions, as outlined below. The

connection of the boost output capacitor on the PCB is

crucial for ripple performance, as discussed in the Pin

Functions section.

Linear Regulator Stability & Output Capacitor

The LT3095 linear regulators are stable with a minimum

output capacitance of 2.2µF (ESR < 0.1Ω). Use low-ESR

multilayer ceramic capacitors and give consideration to

the actual capacitance under bias and temperature condi-

tions. See the Effective Operating Capacitance section for

more information.

Thelinearregulatorfeedbackloophasveryhighbandwidth,

allowing it to respond quickly to load steps and actively

correct input ripple feed-through up to frequencies near

the self-resonance of a typical multilayer ceramic capaci-

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