Linear Technology DC326B Demo Manual

DEMO MANUAL DC326B

NO-DESIGN SWITCHER

OPERATION

How to Measure Voltage Regulation and Efficiency

When measuring voltage regulation or efficiency, voltage measurements should be made directly across the VOUT and GND terminals, not at
the end of test leads at the load. Similarly, input voltage should be measured directly at the VIN and GND terminals of the LT1766 demo board.
Input and output current should be measured by placing an ammeter in series with the input supply and load. Refer to figure 2 for proper
monitoring equipment setup.

How to Measure Output Voltage Ripple

When measuring output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. A sturdy wire should be
soldered to the output side of the GND terminal. The other end of the wire is looped around the ground side of the probe and should be kept
as short as possible. The tip of the probe is touched directly to VOUT (see Figure 3). Bandwidth is generally limited to 20MHz for ripple
measurements. Also, if multiple pieces of line-powered test equipment are used, be sure to use isolation transformers on their power lines
to prevent ground loops, which can cause erroneous results. Figure 4 shows the output voltage ripple with a steady-state load of 1A for the
LT1766.

Heat Dissipation Issues

Since the LT1766 includes a 1.5A onboard power switch, care must be taken not to exceed the 125c maximum operating junction temperature
for the part. A simple technique is to use the PC board as a heat sink. On the LT1766 demo board, the power IC is surrounded by ground plane
on both sides of the PC board. The two sides are connected through vias to better handle the power dissipation. If the LT1766 is laid out on a
multilayer board, there should be metal on the inner layers directly underneath the LT1766. This helps in spreading heat and improves the
power dissipation capability of the PCB.

Note: See 'Thermal Calculations' section in the Applications Information of the LT1766 datasheet.

DEMO MANUAL DC326B

NO-DESIGN SWITCHER

OPERATION

Introduction

The LT1766 is a 1.5A 200kHz Step-Down switching regulator capable of
operation at input voltages as high as 60V. The demonstration circuit shown
in the schematic allows for output selection of 3.3V or 5V using the jumper J1.
The board comes equipped with input (VIN), output (VOUT), GND, SYNC and
S/D terminals to simplify bench testing. The demonstration circuit highlights the
ability of the LT1766 to achieve excellent efficiencies at both high and low
input voltages. The efficiency curves in Figure 1 illustrate both 42V to 5V and
12V to 5V conversions with peak efficiencies of greater than 80% and 90%.

Figure 1. LT1766 efficiency vs. Load Current

Shutdown Pin

For normal operation, the S/D pin can be left floating. S/D has two output-disable modes, lockout and shutdown.
When the pin is taken below the 2.38V lockout threshold, switching is disabled. This is typically used for input undervoltage lockout.
Grounding the S/D pin places the LT1766 in shutdown mode. This reduces total board supply current to typically 25uA.

Synchronization Pin

To synchronize switching to an external clock, apply a logic-level signal to the SYNC pin. Amplitude must be from a logic
low level to greater than 2.2V with a duty cycle from 10% to 90%. Synchronization frequency is possible from 228kHz
up to 700kHz.

Quick Start Guide

A list of procedures for getting started, including the basic set-up for measurement equipment, are provided in the 'quick start guide'
attached.

NOTE: The LT1766 datasheet should be read in conjunction with the demonstration board information provided.

Efficiency vs. Load Current

50

60

70

80

90

100

0.00 0.25 0.50 0.75 1.00 1.25

Load Current (A)

Efficiency (%)

Vin=12V

Vin=42V

Vout = 5V

L = 47uH

DEMO MANUAL DC326B

NO-DESIGN SWITCHER

QUICK START GUIDE

Refer to Figure 2 for proper measurement
setup and follow the procedure outlined below :

1. Connect the input power supply to the VIN and GND 6. Set the output voltage with the jumper J1,
terminals. The input voltage must be between 5.5V and 60V. as shown in the table below.

2. Connect an ammeter in series with the input supply to 7. After all connections are made, turn on input
measure input current. power and verify that the output voltage is correct.

3. Connect either power resistors or an electronic load
to the VOUT and GND terminals.

POSITION OUTPUT VOLTAGE

4. Connect an ammeter in series with the output load to Jumper J1 open 5.0V

measure output current. Jumper J1 inserted 3.3V

5. The S/D pin should be left floating for normal operation
and tied to GND for shutdown.

1

1

2

2

A A

B B

5V/3.3V
LINK

VIN

GND

S/D

GND

VOUT

SYNC

NOTE: UNLESS OTHERWISE SPECIFIED

1. FUSED CORNER PINS 1, 8, 9 ,16 (GND) - U1.

DEMO BOARD RELEASE1 11/29/00

REVISION HISTORY

DESCRIPTION DATE APPROVEDECO REV

LTC CONFIDENTIAL - For Customer Use Only

1

DC326B

Wednesday, November 29, 2000

1

1

A

SCH, 1.5A 200KHz HIGH VOLTAGE BUCK CONVERTER PCB

326Br1.DSN

NONE

L.SANTOS 7/14/00

SIZE

SCALE:

CAGE CODE

DWG NO

REV

SHEET

OF

FILENAME:

TITLE

CONTRACT NO.

APPROVALS

DATE

DRAWN
CHECKED
APPROVED
ENGINEER
DESIGNER

UNLESS OTHERWISE SPECIFIED

DIMENSIONS ARE IN INCHES

TOLERANCE ON ANGLE - - -

2 PLACES - - - 3 PLACES - - -

INTERPRET DIM AND TOL

PER ASME Y14.5M -1994
THIRD ANGLE PROJECTION

DO NOT SCALE DRAWING

TECHNOLOGY

1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: [phone]
Fax: [phone]

E5

Opt.

E4

L1

68uH

C1

1000pF

C2
Opt.

E1

+

C5
100uF
10V

Q1
Opt.

1

2 3

R5
Opt.

E6

R2

15.4K
1%

E2

D1

10MQ060N

R4

19.1K
1%

R3

4.99K
1%

E3

R1
Opt.

+

C3

4.7uF
100V

D3
Opt.

3 1

D2

FMMD914

31

JP1

+

C7
Opt.

R6
Opt.

C9

Opt.

U1
LT1766CGN

24

6

10

11

12

15

14

SWVIN

BOOST

BIAS

VC

FB

SHDN

SYNC

C6

0.47uF
25V

C4

0.33uF

Linear Technology Corporation

LT1766CGN (SSOP16)

Bills Of Material

Demo DC326B

Printed: 6/16/2005

Rev. 2

Item Qty Reference Part Description Manufacture / Part #

1 1 C1 Capacitor, X7R 220pF 50V 10% AVX 08055A221KAT
2 1 C3 Capacitor, chip 4.7uF 100V MARCON THCR70E2A475ZT
3 0 C3 (Option2) Capacitor, chip 150uF 63V AL ELECT PANASONIC ECA63FQ150L
4 1 C4 Capacitor, X7R 0.33uF 16V 10% AVX 0805YC334KAT1A
5 1 C5 Capacitor, Tant. 100uF 10V 20% AVX TPSD107M010R0100
6 1 C6 Capacitor, Y5V 0.47uF 25V 80% AVX 08053G474ZAT1A
7 1 C2 Capacitor, X7R .022uF 16V 10% AVX 0805YC223KAT
8 0 C7 (Option 1) Capacitor, Tant. 100uF 10V 20% AVX TPSD107M010R0100

9 0 C7 (Option 2) Capacitor, X5R, 47uF, 6.3V TAIYO YUDEN JMK432BJ476MM
10 0 C9 (Option) CAP, .1UF, 25V Y5V, 0603 AVX 06033G104ZAT
11 0 C12 (Option) Capacitor, X7R, 1000pF, 50V, 10% AVX 08055C102KAT
12 1 D1 Diode Schottky,1.5A, 60V IR 10MQ060N
13 0 D1 (Option) Diode Schottky,3A, 60V OPT:MOTOROLA MBRS360T4
14 1 D2 Diode, 200mA, 100V ZETEX FMMD914TA
15 0 D3 (Option) Diode, 200mA, 100V
16 6 E1-E6 Test Point, MILL MAX 2501-2
17 1 J1 Header, 2pin, 1 Row, .079CC COMM-CON 2802S-02-G1
18 1 J1 Shunt, .079" center COMM CON CCIJ2MM-138G
19 0 L1 (Option 3) Inductor, 68uH COOPER ELECTRONICS UP2-680
20 1 L1 Inductor, 33uH SUMIDA CDRH125-330MC
21 0 L1 (Option 2) Inductor, 47uH COOPER ELECTRONICS UP2-470
22 0 Q1 (Option) Xstr, NPN, SOT23
23 1 R2 Resistor, Chip 15.4K 1% AAC CR10-1542FM
24 1 R3 Resistor, Chip 4.99K 1% AAC CR10-4991FM
25 1 R4 Resistor, Chip 19.1K 1% AAC CR10-1912FM
26 0 R5 (Option) Resistor, Chip XXK 1% AAC
27 0 R6 (Option) Resistor, Chip 2K 1% AAC
28 1 R1 Resistor, Chip, 2.2K, 5%, 1/8W AAC CR10-222JM
29 1 U1 I.C. LT1766 LINEAR TECHNOLOGY LT1766EGN or LT1766IGN
30 4 MH1-MH4 STAND-OFF, NYLON HEX #4-40x1/4" MICRO PLASTICS #14HTSP101
31 4 MH1-MH4 SCREW, #4-40 x 1/4 ANY

Page 1 - of - 1

Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Analog Devices Inc.:
DC326B