LT3063 datasheet(13/30 Pages) LINEAR

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LT6658

6658f

For more information www.linear.com/LT6658

The LT6658 combines the low noise and accuracy of a

high performance reference and the high current drive of

a regulator. The LT6658 is a high performance regula-

tor providing two precise low noise outputs with Kelvin

sense pins. The isolated outputs maintain their precision

even when large voltage or current transients exist on the

adjacent channel.

The LT6658 architecture consists of a low drift bandgap

reference followed by an optional noise reduction stage

and two independent buffers. The bandgap reference and

the buffers are trimmed for low drift and high accuracy.

The high gain buffers ensure outstanding line and load

regulation.

The guidance that follows describes how to reduce noise,

lower power consumption, generate different output

voltages, and maintain low drift. Also included are notes

on internal protection circuits, PCB layout, and expected

performance.

Supply Pins and Ground

The LT6658 can operate with a supply voltage from

VOUT + 2.5V,to36V.Toprovidedesignflexibility,theLT6658

includes 3 supply pins. The VIN pin supplies power to the

bandgap voltage reference. The VIN1 and VIN2 pins supply

power to buffer amplifiers 1 and 2, respectively. Figure 1

illustrates how current flows independently through each

of the output buffers. The simplest configuration is to

connect all three supply pins together. To reduce power

consumption or isolate the buffer amplifiers, separate the

supply pins and drive them with independent supplies.

SeparateVIN,VIN1andVIN2supplypinsisolatethebandgap

reference and the two outputs VOUT1_F and VOUT2_F from

each other. For example, a load current surge through

VIN1 to VOUT1_F is isolated from VOUT2_F and the bandgap

voltage reference. In Figure 2 a 140mA load current pulse

on buffer 1 and the resulting output waveforms are shown.

Despite the large current step on buffer 1, there is only a

small transient at the output of buffer 2. When providing

a stable voltage reference to quiet circuits like an ADC or

DAC, it is important the two buffer outputs are isolated.

applicaTions inForMaTion

To minimize power consumption each supply pin can

be operated with its minimum voltage. For example, if

Buffer 1 has a 2.5V output, VIN1 can be operated at 5V. If

Buffer 2’s output is run at 3V, run VIN2 at 5.5V. The power

savings gained by minimizing each supply voltage can be

considerable.

Excessivegroundcurrentandparasiticresistanceinground

linescandegradeloadregulation.UnlikeanLDO,theground

currentoftheLT6658isdesignedsuchthatgroundcurrent

does not increase substantially when sourcing a large load

current. All three ground pins and exposed pad should be

connected together on the PCB, through a ground plane

or through a separate trace terminating at a star ground.

The supply pins can be powered up in any order without

an adverse response. However, all three supplies pins

need the minimum specified voltage for proper operation.

LT6658-2.5

+–

6658 F01

INDICATES CURRENT FLOW

–

LOAD2

GND

LOAD1

THERMAL

SHUTDOWN

BANDGAP

VIN1 VIN2

VIN

VOUT1_F

VOUT2_F

1,2

Figure 1. LT6658 Current Flow through the Supply Pins

COUT1 = 10µF

COUT2 = 10µF

LOAD CURRENT

VOUT1

VOUT2

50µs/DIV

20mV/DIV

100mA/DIV

100µV/DIV

6658 F02

Figure 2. 10mA to 150mA Load Step on VOUT1

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