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9

DEMO MANUAL DC257

NO-DESIGN SWITCHER

OPERATIO

U

Table 2. List of Alternative Component Manufacturers

MANUFACTURER

DEVICE

PHONE

FAX

AVX

Capacitors

(843) 448-9411

(843) 448-1943

Central Semiconductor

Diodes

(516) 435-1110

(516) 435-1824

Coilcraft

Inductors

(847) 639-6400

(847) 639-1469

Coiltronics

Inductors

(561) 241-7876

(561) 241-9339

COMM CON

Connectors

(626) 301-4200

(626) 301-4212

Dale

Inductors

(605) 665-1627

(605) 665-0817

International Rectifier

Diodes

(310) 322-3331

(310) 322-3332

Motorola

Diodes

(800) 441-2447

(602) 413-6637

Murata-Erie

Capacitors

(814) 237-1431

(814) 238-0490

Sanyo

Capacitors

(619) 661-6835

(619) 661-1055

(81) 0952-82-3959

(81) 0952-82-4655

Sprague

Capacitors

(207) 324-4140

(207) 324-7223

Sumida

Inductors

(847) 956-0667

(847) 956-0702

(81) 03-3607-5111

(81) 03-3607-5114

TDK

Inductors

(847) 803-6100

(847) 803-6294

TAD

Resistors

(714) 255-9123

(714) 255-9291

Zetex

Diodes

(516) 543-7100

(516) 864-7630

RUN/SOFT-START FUNCTION

The RUN/SS pin (E3) is a dual-purpose pin that provides
the soft-start function and a means to shut down the
LTC1707. Soft-start reduces surge currents from V

IN

 by

gradually increasing the internal current limit. Power sup-
ply sequencing can also be accomplished using this pin.

An internal 2.25

µ

A current source charges an external

capacitor, C

SS

. When the voltage on RUN/SS reaches

0.7V, the LTC1707 begins operating. As the voltage on
RUN/SS continues to increase from 0.7V to 1.8V, the
internal current limit also increases at a proportional linear
rate. The current limit begins at 25mA (at V

RUN/SS 

≤

␣ 0.7V)

and ends at the Figure 4 value (V

RUN/SS 

≥

 1.8V). The output

current thus increases slowly, charging the output capaci-
tor. If RUN/SS has been pulled all the way to ground, there

is a delay before starting of approximately 310ms/

µ

F,

followed by an additional 490ms/

µ

F to reach full current.

C

SS 

= 0.1

µ

F on this PC board.

Pulling the RUN/SS pin below 0.7V (0.4V min) puts the
LTC1707 into a low quiescent current shutdown mode
(I

Q

 < 15

µ

A). See the LTC1707 data sheet for further

information.

COMPONENT MANUFACTURERS

Table 2 is a partial list of manufacturers of components
that can be used in LTC1707 applications. Using compo-
nents other than the ones supplied on the demonstration
board will require careful analysis to verify that all com-
ponent specifications are not exceeded. Finally,
recharacterizing the circuit for efficiency is necessary.

Содержание DC257

Страница 1: ...reduce switching losses and maintain high operating efficiencies In switching noise sensitiveapplications BurstModeoperationcanbeinhib ited by grounding the SYNC MODE pin or synchronizing it with an external clock Gerber files for this circuit board are available Call the LTC factory SYMBOL PARAMETER CONDITIONS JUMPER POSITION VALUE VIN Input Voltage Range 2 85V to 8 5V VOUT Output Voltage See Fig...

Страница 2: ...1 19V IREF Maximum VREF Output Currrent All 100µA Figure 1 LTC1707 Constant Frequency High Efficiency Converter Note 1 Programmable via optional R6 VOUT 0 8V 1 210k R6 PACKAGE A D SCHE ATIC DIAGRA S W U W 1 2 3 4 8 7 6 5 TOP VIEW VREF SYNC MODE VIN SW ITH RUN SS VFB GND S8 PACKAGE 8 LEAD PLASTIC SO LTC1707CS8 VFB GND ITH VIN SW 3 4 1 6 5 ITH VREF RUN SS 2 8 SYNC MODE 7 LTC1707 CC1 CSS 0 1µF CC2 47...

Страница 3: ...000 JP1 1 22025 12 G1 0 079 Double Row Header COMM CON 626 301 4200 JP1 1 CCIJ2MM 138G 0 079 Center Shunt COMM CON 626 301 4200 L1 1 CD54 150MC 15µH 20 Inductor Sumida 847 956 0667 R1 1 CR16 2373FM 237k 1 1 16W Chip Resistor TAD 800 508 1521 R2 1 CR16 1653FM 165k 1 1 16W Chip Resistor TAD 800 508 1521 R3 1 CR16 9762FM 97 6k 1 1 16W Chip Resistor TAD 800 508 1521 R4 1 CR16 7872FM 78 7k 1 1 16W Chip...

Страница 4: ...ixed frequency architecture Burst Mode operation provides high efficiency at low load currents Operatingefficienciestypicallyexceed90 over two decades of load current range 100 duty cycle provides low dropout operation which extends operating time in battery operated systems Do not use small spring clip leads when testing this circuit Solderedwireconnectionsarerequiredtoproperly verify the perform...

Страница 5: ...atch andturnedoffwhenthecurrentcomparator ICOMP resets the RS latch The peak inductor current at which ICOMP resets the RS latch is controlled by the voltage on the ITH pin which is the output of error amplifier EA The VFB pin allows EA to receive an output feedback voltage from an externalresistivedivider Whentheloadcurrentincreases it causes a slight decrease in the feedback voltage relative to ...

Страница 6: ...igh To disable Burst Mode operation and enable PWM pulse skipping mode connect the SYNC MODE pin to GND When the converter uses Burst Mode operation the peak current of the inductor is set to approximately 200mA even though the voltage at the ITH pin indicates a lower value The voltage at the ITH pin drops when the inductor s average current is greater than the load requirement As theITHvoltagedro...

Страница 7: ...e compensation provides stability by preventing sub harmonicoscillations Itworksbyinternallyaddingaramp to the inductor current signal at duty cycles in excess of 40 As a result the maximum inductor peak current is lowerforVOUT VIN 0 4thanwhenVOUT VIN 0 4 Seethe maximum inductor peak current vs duty cycle graph in Figure 4 The graph labeled With External Clock shows the worst case peak current red...

Страница 8: ... 432 1900 DC257 F06 10Ω OPERATIO U This applies to line regulation input to output voltage regulation as well as load regulation tests In doing the line regulation tests always look at the input voltage across the input terminals For the purposes of these tests the demonstration circuit should be powered from a regulated DC bench supply so that variations on the DC input do not add errors to the r...

Страница 9: ...rom VIN by gradually increasing the internal current limit Power sup ply sequencing can also be accomplished using this pin An internal 2 25µA current source charges an external capacitor CSS When the voltage on RUN SS reaches 0 7V the LTC1707 begins operating As the voltage on RUN SS continues to increase from 0 7V to 1 8V the internalcurrentlimitalsoincreasesataproportionallinear rate The curren...

Страница 10: ...10 DEMO MANUAL DC257 NO DESIGN SWITCHER W PCB LAYOUT A U D FIL Component Side Solder Mask Component Side Component Side Silkscreen ...

Страница 11: ... believed to be accurate and reliable However no responsibility is assumed for its use Linear Technology Corporation makes no represen tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights W PCB LAYOUT A U D FIL Pastemask Solder Side Solder Side Solder Mask ...

Страница 12: ...CIFIED 1 MATERIAL FR4 OR EQUIVALENT EPOXY 2 OZ COPPER CLAD THICKNESS 0 062 0 006 TOTAL OF 2 LAYERS 2 FINISH ALL PLATED HOLES 0 001 MIN 0 0015 MAX COPPER PLATE ELECTRODEPOSITED TIN LEAD COMPOSITION BEFORE REFLOW SOLDER MASK OVER BARE COPPER SMOBC 3 SOLDER MASK BOTH SIDES USING SR1020 OR EQUIVALENT 4 SILKSCREEN USING WHITE NONCONDUCTIVE EPOXY INK 5 ALL DIMENSIONS IN INCHES 6 SCORING 0 017 SYMBOL A B...

Страница 13: ...Mouser Electronics Authorized Distributor Click to View Pricing Inventory Delivery Lifecycle Information Analog Devices Inc DC257A ...

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