Linear Technology 1060 Manual de usuario

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1060

DUAL MONOLITHIC STEP-DOWN SWITCHING REGULATOR

LT3508

DESCRIPTION

Demonstration circuit 1060 features two LT3508

step-down DC/DC switching converters. One circuit

uses the LT3508EFE and the other circuit has the

LT3508EUF. The LT3508 dual output step-down

switching regulator has two internal power

switches, a wide input voltage range, adjustable

switching frequency synchronizable over the fre-

quency range, programmable soft-start, tracking,

power-good, and channel sequencing. The anti-

phase switching reduces the input capacitor. The

wide V

range of the LT3508 allows step-down

configurations with up to 36V

input. The high power

internal switches have current limit that allows for

up to 1.4A output on each output.

The demonstration circuit has two circuits. The top

is optimized for high efficiency, wide input range

and maximum output current; the bottom is opti-

mized for the size. The top circuit is rated for 3.3V

at 1.4A and 5V at 1.4A output from a 6V–36V input

using the FE package. The frequency is set to

700kHz to allow for the high VIN to VOUT ratio and

provides high efficiency throughout the range. The

bottom circuit generates 1.8V at 1A and 3.3V at 1A

from a 5V to 16V DC input using the QFN package

and shows off the compact size with 1.6MHz

switching frequency. The two channels are se-

quenced so that the 1.8V channel starts before the

3.3V channel. The two circuits are completely iso-

lated from each other and can be run simultane-

ously or independently. The shutdown terminals are

available on each circuit as are the power good and

track terminals in case sequencing or tracking is

preferred.

This board is designed for applications that require

two step-down converters up to 1.4A load with low

cost, small board space, low parts count, and sim-

ple circuit design. The high current, on-board, dual

monolithic switches eliminate the need for external

switches. The current-mode control simplifies the

compensation network and gives excellent transient

response.

Please read the LT3508 datasheet in addition to this

quickstart guide for details regarding LT3508 opera-

tion and applications.

Design files for this circuit board are available.

Call the LTC factory.

LT is a trademark of Linear Technology Corporation

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1060

DUAL MONOLITHIC STEP-DOWN SWITCHING REGULATOR

TYPICAL PERFORMANCE (T

= 25°C)

60%

65%

70%

75%

80%

85%

90%

95%

100%

0 0.5 1 1.5

C H1, C H2 LO AD C URRE NT (mA )

E F F IC IE NC Y (%)

6V IN

18VIN

12VIN

3.3V, 5V

outputs

Figure 1. Typical Efficiency of DC1060A LT3508EFE Dual Step-

Down VOUT1=3.3V, VOUT2=5V

Table 1.

FE package Dual Step-Down Converter (VOUT1=3.3V

and VOUT2=5V)

Parameter Value

6V to 36V

OUT1

3.3V

OUT

2 5V

OUT

1 Load Current 1.4A(max)

OUT

2 Load Current 1.4A(max)

Switching frequency 700kHz

OUT

1 Ripple pk-pk 25mV at 1.4A and 18VIN

OUT

2 Ripple pk-pk 18mV at 1.4A and 18VIN

Efficiency 86% at 1.4A load current (VOUT1

and VOUT2) and 12VIN

60%

65%

70%

75%

80%

85%

90%

95%

100%

0 0.25 0.5 0.75 1

C H1, C H2 LO A D C URRE NT (mA )

E F F IC IE N C Y (%)

5V IN

16VIN

12VIN

1.8V, 3.3V

outputs

Figure 2. Typical Efficiency of DC1060A LT3508EUF Dual Step-

Down VOUT1=1.8V, VOUT2=3.3V

Table 2.

QFN Package Dual Step-Down Converter (VOUT1=1.8V

and VOUT2=3.3V)

Parameter Value

5V to 16V

VOUT1 1.8V

VOUT2 3.3V

VOUT1 Load Current 1A(max)

VOUT2 Load Current 1A(max)

Switching frequency 1.6MHz

OUT

1 Ripple pk-pk 3mV at 1A and 12VIN

OUT

2 Ripple pk-pk 5mV at 1A and 12VIN

Efficiency 85% at 500mA load current

(VOUT1 and VOUT2) and 5VIN

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1060

DUAL MONOLITHIC STEP-DOWN SWITCHING REGULATOR

QUICK START PROCEDURE

DC1060A is easy to set up to evaluate the perform-

ance of the LT3508. Refer to Figure 3 for proper

measurement equipment setup and follow the proce-

dure below:

LT3508EFE top circuit:

Connect a 6V–36V DC input power supply to the

VIN and GND terminals on the board with power

OFF.

Attach the desired load to each channel – up to

1.4A.

After all connections are made, turn ON input

power and verify that the output voltages are 3.3V

and 5V.

The Track/SS, power good (PG), and shutdown

functions are optional and their terminals can be

left floating (disconnected). Connecting the shut-

down terminal to the GND terminal shuts down the

circuit and drops the output voltages to zero. Shut-

down has a pull-up resistor on circuit that may not

be necessary with the proper high and low signal

applied.

LT3508EUF bottom circuit

1. Use the same testing method for the bottom cir-

cuit as used in the top circuit, but with a different

input voltage (5V to 16V), load currents (1A per

channel maximum), and output voltages (1.8V

and 3.3V).

2. Upon startup, sequencing of VOUT1 and VOUT2

can be observed with an oscilloscope.

Figure 3. Proper Measurement Equipment Setup

SYNC FUNCTION

The Rt/Sync pin can be used for synchronization of the LT3508 internal oscillator to an external source. To use

the sync function, remove R2 (in the top FE circuit) or R13 (in the bottom UF circuit), and attach the external

sync signal to the Rt/Sync pin directly or to the now-unstuffed resistor pad tied to the Rt/Sync pin.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1060

DUAL MONOLITHIC STEP-DOWN SWITCHING REGULATOR

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DC1060A

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