LT3071MPUFD View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LT3071MPUFD

5A, Low Noise, Programmable Output, 85mV Dropout Linear Regulator with Analog Margining

Linear Technology 

LT3071

APPLICATIONS INFORMATION

SWITCHING REGULATOR

REF +

PWM

–

FB

ITH

IN

LT3071

OUT

LOAD

VOUT +

VREF 300mV

REFERENCE

VIOC

3071 F02

Figure 2. VIOC Control Block Diagram

PWRGD—Power Good

PWRGD pin is an open-drain NMOS digital output that

actively pulls low if any one of these fault modes is detected:

• VOUT is less than 90% of VOUT(NOMINAL) on the rising

edge of VOUT .

• VOUT drops below 85% of VOUT(NOMINAL) for more than

25µs.

• VBIAS is less than its undervoltage lockout threshold.

• The OUT-to-IN reverse-current detector activates.

• Junction temperature exceeds 145°C typically.*

*The junction temperature detector is an early warning

indicator that trips approximately 20°C before thermal

shutdown engages.

Stability and Output Capacitance

The LT3071’s feedback loop requires an output capacitor

for stability. Choose COUT carefully and mount it in close

proximity to the LT3071’s 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 applica-

tions present the best case layout scenario for extracting

full LT3071 performance.

Low ESR, X5R or X7R ceramic chip capacitors are the

LTC recommended choice for stabilizing the LT3071. Ad-

ditional bulk capacitors distributed beyond the immediate

decoupling capacitors are acceptable as their parasitic ESL

and ESR, combined with the distributed PCB inductance

isolates them from the primary compensation pole provided

by the local surface mount ceramic capacitors.

The LT3071 requires a minimum output capacitance of

15µF for stability. LTC strongly recommends that the output

capacitor network consist of several low value ceramic

capacitors in parallel.

Why Do Multiple, Small-Value Output Capacitors

Connected in Parallel Work Better?

The LT3071’s unity-gain bandwidth with COUT of 15µF is

about 1MHz at its full-load current of 5A. Surface mounted

MLCC capacitors have a self-resonance frequency of

fR = 1/(2π√LC), which must be pushed to a frequency higher

than the regulator bandwidth. Standard MLCC capacitors

are acceptable. To keep the resonant frequency greater

than 1MHz, the product 1/(2π√LC) must be greater than

1MHz. At this bandwidth, PCB vias can add significant

inductance, thus the fundamental decoupling capacitors

must be mounted on the same plane as the LT3071.

3071fc

18

For more information www.linear.com/LT3071

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