DC639A - ANALOG DEVICES - Datasheet.Live

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 639

1.5A, 500KHZ STEP-DOWN CONVERTER WITH BURST MODE

LT1977

DESCRIPTION

Demonstration circuit 639 is a monolithic step-down

DC/DC switching converter featuring the LT®1977.

The board is optimized for 3.3V output at up to 1A

load current for a steady state input voltage range of

4V to about 36V* with input transients up to 60V .

Minimum on-time restrictions and 3.3V output may

limit the steady state maximum input voltage to 36V

before pulse skipping occurs

With its wide input

voltage range, 1.5A internal power switch, 100µA

supply current (at input voltages above 14V), 500kHz

switching frequency and thermally enhanced pack-

age, the LT1977 is a very versatile and powerful IC for

DC/DC converters that require compact space, high

efficiency at both heavy and light loads and high input

voltage.

The LT1977 500kHz switching frequency allows all of

the components to be small, surface mount devices.

Synchronization with an external clock of up to

700kHz is possible. The current-mode control topol-

ogy creates fast transient response and good loop

stability with a minimum number of external compo-

nents. The low resistance internal power switch

(0.2Ω) achieves high efficiencies of up to 80%. The

shutdown pin can be used to program undervoltage

lockout or place the part in micropower shutdown,

reducing supply current to less than 1µA by driving

the pin low. Burst Mode™ reduces zero load current

to under 100µA at most input voltages while main-

taining a regulated output. A power good comparator

and a timing delay can be used for additional system

diagnostics and sequencing. The soft start function

reduces inrush current at soft start and output volt-

age overshoot. An optional Power Good Feedback

output terminal can be used to monitor or control

power good feedback externally.

The LT1977 datasheet gives a complete description of

the part, operation and applications information. The

datasheet must be read in conjunction with this Quick

Start Guide for demonstration circuit 639. In particu-

lar, the datasheet section on ‘Thermal Calculations’ is

important for estimating whether a given application’s

combination of input voltage, load current and fre-

quency will cause the LT1977 to exceed it’s absolute

maximum rated junction temperature. The LT1977 is

assembled in a small 16-pin thermally enhanced

package with exposed pad where proper board layout

is essential for maximum thermal performance. See

the datasheet section ‘Layout Considerations’.

Design files for this circuit board are available. Call

the LTC factory.

LT is a trademark of Linear Technology Corporation

QUICK START PROCEDURE

Demonstration circuit 639 is easy to set up to evalu-

ate the performance of the LT1977. Refer to Figure 1.

for proper measurement equipment setup and follow

the procedure below:

NOTE:

Make sure that the input voltage does not ex-

ceed 60V.

NOTE:

The synchronization, shutdown, and power

good functions are optional and their terminals can

be left floating (disconnected) if their functions are

not being used.

NOTE:

Do not hot-plug the input voltage terminal VIN.

The absolute maximum voltage on VIN is 60V and

hot-plugging a power supply through wire leads to

the demonstration circuit can cause the voltage on

the extremely low-ESR ceramic input capacitor to ring

to twice its DC value. This is due to high currents in-

stantaneously generated in the inductive supply leads

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 639

1.5A, 500KHZ STEP-DOWN CONVERTER WITH BURST MODE

from an input voltage step on the low-ESR ceramic

input capacitor. A bulky higher-ESR capacitor, and an

additional inductive filter can be added to the circuit

to dampen hot-plug transient ringing.

See Application

Note 88 for more details.

In order to protect the IC, a

transient voltage suppressor diode can be added be-

tween VIN and GND terminals to absorb any high

voltage transient ringing that may occur due to hot-

plugging.

NOTE:

Connect the power supply (with power off),

load, and meters as shown in Figure 1.

After all connections are made, turn on input power

and verify that the output voltage is 3.3V.

NOTE:

If the output voltage is too low, temporarily

disconnect the load to make sure that the load is

not set too high.

Once the proper output voltages are established,

adjust the load within the operating range and ob-

serve the output voltage regulation, ripple voltage,

efficiency and other parameters.

Figure 1. Proper Measurement Equipment Setup

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 639

1.5A, 500KHZ STEP-DOWN CONVERTER WITH BURST MODE

4 4

3 3

2 2

1 1

Gnd

SHDN

SYNC

PGOOD PGFB

Vin

4V-60V*

OPTION

1812

AVX

D-CASE

* Transients Up to 60V, See Quick Start Guide

Vout

Circuit That Meets Customer-Supplied Specifications;

LTC CONFIDENTIAL - FOR CUSTOMER USE ONLY

Linear Technology Has Made A Best Effort To Design A

Supplied For Use With Linear Technology Parts.

This Circuit Is Proprietary To Linear Technology And

Circuit Board Layout May Significantly Affect Circuit

Applications Engineering For Assistance.

Application. Component Substitution And Printed

However, It Remains The Customer's Responsibility To

Performance Or Reliability. Contact Linear Technology

Verify Proper And Reliable Operation In The Actual

Customer Notice

3.3V at 1A

6.3V

NIOBIUM

80mOhm

DEMO 639A LT1977IFE

High Voltage 1.5A 500kHz Step-Down Converter with Burst Mode

LINEAR TECHNOLOGY CORPORATION

1630 McCARTHY BLVD.

MILPITAS, CA. 95035

408-432-1900

408-434-0507 FAX

1 1Monday, August 23, 2004

Title

Size Document Number Rev

Date: Sheet of

Vout

Vin

TP6

2.2uF

TDK

100V

C10

(Opt.)

C11

10pF

TP7

0.01uF

TP8

200k

R10

100k

TP4

330pF

24k

TP3

TP5

1500pF

(Opt.)

R11

(Opt.)

0.01uF

165k

TP2

0.1uF

R12

(Opt.)

1N4148W

B260A

15uH

CDRH6D28-150NC

(Opt.)

100uF

100k

LT1977IFE

VIN

SHDN

SYNC

PGFB

GND

CSS

BIAS

BOOST

N/C

TP1

Linear Technology Corporation

LT1977IFE

Bill Of Material

Demo Bd. #639A

6/17/2005

Item Qty Reference Part Description Manufacture / Part #

1 1 C11 CAP., NPO, 10pF, 25V, 5% AVX 06033A100JAT2A

2 1 C1 CAP., NPO , 330pF, 25V, 5% AVX 06033A331JAT2A

3 1 C2 CAP., NPO, 1500pF, 25V, 5% AVX 06033A152JAT2A

4 1 C3 CAP., X7R, 2.2uF, 100V, 10% TDK C4532X7R2A225K

5 2 C7,C8 CAP., X7R, 0.01uF, 16V, 10% AVX O603YC103KAT

6 1 C4 CAP., X7R 0.1uF 16V 20% TAIYO YUDEN EMK107BJ104MA

7 1 C5 CAP., Niobium 100uF 6.3V D case AVX NOSD107M006

8 0 C6,C10 (OPT)

9 1 D1 DIODE, chottky Rect., 2.0Amp\60V DIODES INC. B260A-13 SMA

10 1 D2 DIODE, Switching Diode DIODES INC., 1N4148W-7 SOD123

11 0 D4 (OPT)

12 1 L1 INDUCTOR, 15uH SUMIDA CDRH6D28-150NC

13 1 R10 RES., Chip 0 AAC CJ06-000M

14 1 R2 RES., Chip 165K 0.06W 1% AAC CR16-1653FM

15 2 R3,R8 RES., Chip 100K 0.1W 1% AAC CR16-1003FM

16 1 R9 RES., Chip 200K 0.06W 5% AAC CR16-204JM

17 2 R1,R4 RES., Chip 24K 0.06W, 5% AAC CR16-243JM

18 0 R11,R12 (OPT)

19 7 TP1-TP7 TURRET, Testpoint Mill Max 2501-2

20 0 TP8 (OPT)

21 1 U1 I.C., Step-Down Reg. Linear Tech. Corp. LT1977IFE ***

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