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 Efficiency vs. Load Current 100 Vout = 5V L = 47uH Vin=12V 90 Efficiency (%) 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%. 80 Vin=42V 70 60 50 0.00 0.25 0.50 0.75 1.00 1.25 Load Current (A) 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. 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 terminals. The input voltage must be between 5.5V and 60V. 6. Set the output voltage with the jumper J1, as shown in the table below. 2. Connect an ammeter in series with the input supply to measure input current. 7. After all connections are made, turn on input power and verify that the output voltage is correct. 3. Connect either power resistors or an electronic load to the VOUT and GND terminals. 4. Connect an ammeter in series with the output load to measure output current. 5. The S/D pin should be left floating for normal operation and tied to GND for shutdown. POSITION Jumper J1 open Jumper J1 inserted OUTPUT VOLTAGE 5.0V 3.3V 1 2 REVISION HISTORY LTC CONFIDENTIAL - For Customer Use Only ECO REV 1 DESCRIPTION DATE DEMO BOARD RELEASE APPROVED 11/29/00 D2 FMMD914 1 D3 Opt. C4 0.33uF E1 3 VIN L1 E5 VOUT 1 + C3 4.7uF 100V 6 Opt. E2 GND 4 VIN E3 S/D + C5 100uF 10V U1 LT1766CGN + C7 Opt. R2 15.4K 1% R4 19.1K 1% C6 0.47uF 25V D1 SW E4 JP1 2 GND 10MQ060N 15 SHDN BIAS 10 14 SYNC FB 12 5V/3.3V LINK VC E6 C9 Opt. 11 SYNC A 68uH BOOST A 3 C1 1000pF R6 Opt. 3 R1 Opt. Q1 Opt. 1 R5 Opt. 2 C2 Opt. R3 4.99K 1% NOTE: UNLESS OTHERWISE SPECIFIED 1. FUSED CORNER PINS 1, 8, 9 ,16 (GND) - U1. B B 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 CONTRACT NO. APPROVALS DATE DRAWN L.SANTOS 7/14/00 TECHNOLOGY 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 TITLE CHECKED SCH, 1.5A 200KHz HIGH VOLTAGE BUCK CONVERTER PCB APPROVED ENGINEER DESIGNER SIZE CAGE CODE DWG NO A DO NOT SCALE DRAWING 1 Wednesday, November 29, 2000 SCALE: NONE REV DC326B FILENAME:326Br1.DSN 2 SHEET 1 1 OF 1 Linear Technology Corporation LT1766CGN (SSOP16) Item Qty Reference 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 1 0 1 1 1 1 0 0 0 0 1 0 1 0 6 1 1 0 1 0 0 1 1 1 0 0 1 1 4 4 C1 C3 C3 (Option2) C4 C5 C6 C2 C7 (Option 1) C7 (Option 2) C9 (Option) C12 (Option) D1 D1 (Option) D2 D3 (Option) E1-E6 J1 J1 L1 (Option 3) L1 L1 (Option 2) Q1 (Option) R2 R3 R4 R5 (Option) R6 (Option) R1 U1 MH1-MH4 MH1-MH4 Printed: 6/16/2005 Rev. 2 Bills Of Material Demo DC326B Part Description Capacitor, X7R 220pF 50V 10% Capacitor, chip 4.7uF 100V Capacitor, chip 150uF 63V AL ELECT Capacitor, X7R 0.33uF 16V 10% Capacitor, Tant. 100uF 10V 20% Capacitor, Y5V 0.47uF 25V 80% Capacitor, X7R .022uF 16V 10% Capacitor, Tant. 100uF 10V 20% Capacitor, X5R, 47uF, 6.3V CAP, .1UF, 25V Y5V, 0603 Capacitor, X7R, 1000pF, 50V, 10% Diode Schottky,1.5A, 60V Diode Schottky,3A, 60V Diode, 200mA, 100V Diode, 200mA, 100V Test Point, Header, 2pin, 1 Row, .079CC Shunt, .079" center Inductor, 68uH Inductor, 33uH Inductor, 47uH Xstr, NPN, SOT23 Resistor, Chip 15.4K 1% Resistor, Chip 4.99K 1% Resistor, Chip 19.1K 1% Resistor, Chip XXK 1% Resistor, Chip 2K 1% Resistor, Chip, 2.2K, 5%, 1/8W I.C. LT1766 STAND-OFF, NYLON HEX #4-40x1/4" SCREW, #4-40 x 1/4 Page 1 - of - 1 Manufacture / Part # AVX 08055A221KAT MARCON THCR70E2A475ZT PANASONIC ECA63FQ150L AVX 0805YC334KAT1A AVX TPSD107M010R0100 AVX 08053G474ZAT1A AVX 0805YC223KAT AVX TPSD107M010R0100 TAIYO YUDEN JMK432BJ476MM AVX 06033G104ZAT AVX 08055C102KAT IR 10MQ060N OPT:MOTOROLA MBRS360T4 ZETEX FMMD914TA MILL MAX 2501-2 COMM-CON 2802S-02-G1 COMM CON CCIJ2MM-138G COOPER ELECTRONICS UP2-680 SUMIDA CDRH125-330MC COOPER ELECTRONICS UP2-470 AAC CR10-1542FM AAC CR10-4991FM AAC CR10-1912FM AAC AAC AAC CR10-222JM LINEAR TECHNOLOGY LT1766EGN or LT1766IGN MICRO PLASTICS #14HTSP101 ANY