LT3045 datasheet(33/62 Pages) AD

33 / 62 page

Data Sheet

LT3074

analog.com

Rev 0.

33 of 62

Figure 83. Output Capacitor, SETCAP Capacitor, and SETRES Resistor Connections for Best Performance

Stability and Output Capacitance

The LT3074 requires a minimum output capacitance of 10µF for stability. Analog Devices recommends the use of low

ESR, X5R, or X7R ceramic capacitors near the LT3074 OUT and GND pins. Include wide routing planes for OUT and

GND to minimize inductance. If possible, mount the regulator immediately adjacent to the application load to

minimize distributed inductance for optimal load transient performance. Point-of-load applications present the best

case layout scenario for extracting the full LT3074 performance.

Additional ceramic capacitors distributed beyond the immediate decoupling capacitors are acceptable and

recommended at the point of load because the distributed PCB inductance isolates them from primary

compensation capacitors.

Many of the applications in which the LT3074 excels, such as field programmable gate arrays (FPGA), application-

specific integrated circuit (ASIC) processors, or digital signal processors (DSP) supplies, typically require a high-

frequency decoupling capacitor network for the device being powered. This network generally consists of many low-

value ceramic capacitors in parallel. In parallel, multiple low-value capacitors present a favorable frequency

characteristic that reduces the parasitic inductance of the capacitors.

Given the high PSRR and low noise performance attained using a single 10µF ceramic output capacitor, larger values

of output capacitors are not necessary. However, these capacitors can still improve the performance. See the Typical

Performance Characteristics section for additional information. Moreover, larger output capacitance does decrease

peak output deviations during a load transient. Note that bypass capacitors used to decouple individual components

Give extra consideration to the type of ceramic capacitors used. The capacitors are manufactured with a variety of

dielectrics, each with different behaviors across temperature and applied voltage. The most common dielectrics

used are specified with electronic industries alliance (EIA) temperature characteristic codes of Z5U, Y5V, X5R, and

X7R. The Z5U and Y5V dielectrics are good for providing high capacitance in the small packages, but these dielectrics

tend to have stronger voltage and temperature coefficients, as shown in Figure 84 and Figure 85. When used with a

5V regulator, a 16V, 10µF Y5V capacitor can exhibit an effective value as low as 1µF to 3µF for the DC bias voltage

applied over the operating temperature range.

CSETCAP

4.7µF

COUT

10µF

CIN

47µF

CBIASDF

0.47µF

MPWR

RPG

IREF

RFS

RSETRES

RASELBOT

RASELTOP

RSMBALERT

RSCL

RSDA

CBIASAF

2.2µF

RPG2

RPG1

RPAR

LT3074

BIAS

BIASDF

OUT

SENSE

SETCAP

IMON

SDA

SCL

ALERT

ASEL

AGND

EN/UV

VIN

VOUT +0.1V TO 5.5V

VBIAS

2.375V TO 5.5V

VOUT

0.5V TO 4.2V

3A MAX IOUT

VIOC

CLKDIS

SETRES

BIASAF

TO PMBus

CONTROLLER

DGND

PGFB

PARASITIC

TRACE RESISTANCE

LT3045 Datasheet(PDF) 33 Page - Analog Devices

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