LT3074AVPBF datasheet(40/62 Pages) AD

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Data Sheet

LT3074

analog.com

Rev 0.

40 of 62

Figure 87. Evaluation Board Layout

High Efficiency Linear Regulator – Input-to-Output Voltage Control

The VIOC pin controls an upstream switching converter to maintain a constant voltage across the LT3074, regardless

of the LDO’s output voltage. This maximizes efficiency while maintaining PSRR performance. The VIOC pin is the

output of a fast amplifier and equals (VIN − VOUT) + 800mV. As shown in Figure 88, the VIOC feature is simple to use. In

the case of switching converters with feedback voltage, VFB ≥ 1V, connect the VIOC pin to the upstream switching

converter’s feedback (FB) pin. This regulates the LT3074 device’s input-to-output differential to the switching

converter’s feedback voltage minus 800mV. When paralleling multiple LT3074 devices, connect the VIOC pin of one

of the LT3074 device to the switching converter’s FB pin and float all other VIOC pins. When LT3074 is turned off, VINLDO

is clamped to a voltage set by VFBSWITCHER × (R1 + R2)/R1.

Figure 88. Basic VIOC Operation

While the VIOC buffer is inside the switching converter’s feedback loop, given the VIOC buffer’s high bandwidth, the

switching converter’s frequency compensation need not be adjusted. Phase delay through the VIOC buffer is typically

less than 2° for frequencies as high as 100kHz. Hence, within the switching converter’s bandwidth (usually much less

than 100kHz), the VIOC buffer is transparent and acts like an ideal wire.

CSETCAP

4.7µF

COUT

10µF

CIN

RPG1

30kΩ

RPG2

15kΩ

RSETRES

5kΩ

800mV

51kΩ

RASELTOP

RASELBOT

0.47µF

2.2µF

LSW

LT3074

BIAS

BIASDF

OUT

SENSE

SETCAP

IMON

SDA

SCL

ALERT

ASEL

AGND

VINLDO

VOUTLDO = 0.5V

IOUT(MAX) = 3A

VIOC

CLKDIS

SETRES

BIASAF

DGND

PGFB

1×

–

VBIAS

VIN

EN/UV

VIN

UPSTREAM

DC-DC

CONVERTER

VFB >= 1V

VFBSWITCHER

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